We have hydronic radiant heat in the basement, currently with a boiler in an all electric house. 4 years ago when we built the structure, the plan ended up to use an air-source heat pump for forced air heating in main floor, and forced air cooling of the whole house, with the boiler doing just basement radiant since that was the option we could afford at that time. In the end we got as far as installing the ductwork and stopped there because of budget/financing reasons. So we have no heat pump/blower/ or AC. Just ductwork and basement radiant heat system. We live in the basement, main floor remains unfinished.

We're now currently collecting bids/estimates to finish the main floor/house all at once, and we thought we'd revisit the geothermal issue again and see if we should go that route. Planned insulation in walls is ~ R32, with attic insulation ~R80+, windows are marvin integrity, and a blower door test is planned for infiltration testing. We're not sure that geo would truly make sense since our rates are very low right now $0.046/KWH for heating, $.065/KWH for cooling, so I plan on requesting a cost comparison of going geo vs. air source and figuring out some sort of ROI to justify the geo investment, since it is a little higher than the air-source pump, even after rebates and credits.

We'd like to add hydronic radiant heat in the main floor, NRT Radiant would be handling the radiant design and I have an estimate of that cost, and it would be DIY install. It seems that forced air cooling is what would make sense since we already have the ductwork for that.

Option 1: Stick with original plan air source heat pump for main floor heating, whole house cooling, boiler for basement radiant. I have an estimate for this option.

Option 2: Boiler radiant heat basement and main floor, with just a central A/C unit for the cooling

Option 3: geothermal combination unit to run hydronic heat whole house and forced air cooling. I'd like to know some brands that could handle this so I can look for local reps/installers for said brands and collect bids/estimates. Would waterfurnace and hydron module be an option? Any others?

Option 4: Geothermal combination unit for hydronic radiant only in basement, forced air heat in main floor, and forced air cooling with geothermal. I wonder that if a combo unit can do option 3 above, why look at option 4? But this might have to be considered if because of budget we cannot have the main floor radiant that I want since all we'd be saving is the cost of the radiant parts.

Option 5: hydronic only in basement with boiler since system is already in place,  and only forced air heat in main floor, and cooling with geothermal. Would this mean a smaller geo vs. option 3 and 4 since it's only handling main floor load, depending on cooling load? Would this would be a direct comparison vs. option 1?

Not sure how feasible/possiblethese options would be, or which I should truly consider, but I'd like to compare if possible. What would be things to consider of one option vs. the others?

Once we get an appraisal ordered and bank approval, we will truly know what our final budget numbers will be, but I'd like to have this figured out before then.

Any feedback or guidance is greatly appreciated.

Thanks.

Load calculations are a critical part to determining which system best suits your needs. Geography does as well since all systems perform better in some areas than others.

Thanks Joe. My first question to anyone I potentially interview is if they do a heat load calculation. I am considering purchasing the H.O. Hvac calc to do my own to compare what they propose for sizing of each system option, just because of past experience where the load numbers I've received from a couple of HVAC contractors seemed way too high. Two instances I got quoted a 5 ton geo unit. But they would not show me their load calculations, just the final number, which is fine. Eventually one confessed that they really didn't do a heat load, and the size was merely based on past homes with similar floorplans. BUt that was 4 years ago. It seems around here because of city ordinances, heat loads are a must, so more contractors seem to do them.

I wouldn't expect to just get the heat loads to be freely handed over without some sort of fee or commitment to go with them, but I really want to have something that I can be fairly confident is close to what my loads should be to compare proposed sizing.

I'm in central Iowa, and assuming all contractors do the loads in similar fashion and come out to about the same number... with that in mind, how would I reasonably compare between options other than just actual cost?

I asked one contractor to do a cost analysis of geo vs air pump, and he compared a geo unit sized to do just the forced air upstairs + cooling, vs. an air pump sized to include the basement radiant as well. It took me a while to decipher the cost comparison to realize that was happening. In that case geo seemed like a no brainer, but including running the radiant with the boiler, the monthly savings didn't seem to justify the geo investment (based on his cost comparison).

If I wanted to truly compare between the options in my first post, how would I do a cost analysis to compare operation of each option so I'm comparing apples to apples as closely as possible? That would help us determine which option is worth the investment for our case.

Also, for a combination geothermal unit to do forced air and hydronic radiant, would those be waterfurnace and hydron module? Any others? I'd like to find local installers and I believe these two brands do have them around here. But I'd like to visit with more, if possible.

Thanks.

With known load any contractor with the software can easily do op cost calcs. It would take me 2 minutes if I knew your load and closest major city + fuel and elec costs.

Have a blower door test performed BEFORE drywall goes up so as to have a chance to find and fix air leaks rather than merely living with the result.

R32 walls doesn't always mean R32 whole-wall R- there is significant thermal bridging in a stick built. In another thread you wrote:

"1" of ISO on exterior, and I wanted to install 1-2" cc spray foam then fill the rest with wet spray or dense packed cellulose.

How does this compare to a wet spray cellulose? Installer said with the wet spray the the value would be R23 for the 2x6 wall."

With 1" of iso on the exterior and a flash'n'fill, with 25% framing fraction you're looking at whole-wall performance of ~R22, not R32, or a U-factor of about 0.045 BTU/hr per square foot of wall area per degree-F of difference.

From your basic building plan & R/U values it's pretty easy to do a quick & dirty heat loss calc with a spreadsheet.

If your outside design temp is about -7F (this is IA, right?) and the interior design temp is 68F, that's a 75F difference, so for every square foot of wall adds a heat load of (75 x 0.045=) 3.4 BTU to the heat load number. Look up your 99% outside design temp number for a nearby city here:

http://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/Outdoor_Design_Conditions_508.pdf

But I'll use a delta-T of 75F just to make the arithmetic easy...

The Marvin integrity series varies with U-factors from 0.28 to 0.33, so call it U0.30. That adds (75x 0.30=) 23 BTU to the heat load for every square foot of glass.

Your roof-R gives you a U-factor of 0.013, or about 1BTU/square foot over the footprint of the house at a 75F delta-T

You'll have to fudge something for your foundation & slab insulation. If the foundation walls aren't insulated it could easily swamp the heat load picture. If you count just the heat loss of the upper half of the foundation (down to a couple feet below the frost line) based on the R value (U-factor=1/R) it'll probably make up for any losses to the ground through the slab, etc.

Then subract 250BTU/hr for every adult human, subtract some for your background plug-loads, add some for your actual infiltration/ventilation, but with an air-tight house and HRV 3000 BTU/hr would probably be more than enough margin.

My guess is that unless you have a HUGE amount of glass, with R22 whole-wall and R75- R80 roof you're looking at less than 3 tons for an average sized house, maybe under 2 tons.

Thanks Dana1. How do you estimate the % of framing fraction for walls? I figure I can literally walk up there, count the number of studs on the exterior perimeter, and figure the square footage of lumber to get it exact. But I'm sure there's an easier way?

The basement is ICF, and manufacturer claims R28 (2.5" of foam on either side of concrete) and there's r10 under the slab, and perimeter of slab is against ICF wall. But it is a full walkout on the back, so counting the basement, there are quite a few windows. The stickers on the windows claim .29 for a U-factor.

Looking at the chart for design temperature, it says -7 for the 99% heating. Two of the HVAC contractors said they used -15 as design outdoor temp. for our area. Would those extra degrees make much of a difference? Also, I think they use 72 for indoor temp. Would that basically translate that you'd need bigger equipment to meet the load, since they are designing for an 87ºF deltaT?

Thanks!

We have contractors around here who inexplicably lower design temp. (I think it's a CYA move). It absolutely affects unit and duct size.....all at your expense.
Manual J is designed with fudge factor in it to begin with.

Framing fractions vary all over the place, it depends on the stud spacing, whether double vs. single top/bottom plates were used, whether code requires mid-level fire blocking, how window & door fraiming was detailed, etc., the number of bump-outs (that add corner framing) etc. A well thought out framing design attempting to minimize thermal bridging on simple rectangular footprint house might drop below 20%, a more complicated design with fire-blocking or seismic-resistance requirements might hit 30%. I tend to use 20% for simpler designs or for 24% o.c. framing, but the national average for tract-house builders at 16" o.c. framing is closer to 25%, so use 25% unless you did your homework on the framing design- it'll be close enough. If you think it's actually 20%, use 0.043 as the U-factor rather than 0.045- which is still not going to make huge delta on the whole house number.

The R28 ICF is a dynamic mass-effect fudge factor number, but adequate for use in system sizing. Steady state the 5" of foam is about R20 @ 75F +/- 25F, but rise about 5% for an average when it's 0F outside, the concrete, interior finish and air films add another ~R1 so call it R22-ish steady-state at design temp. The U-factor assuming the R28 is ~0.036BTU/hr per degree-F delta. If you used R22 (to worst-case it, adding unnecessary margin) it would be 0.045 BTU/hr per degree-F. For yuks you could split the difference and call it 0.040. Unless you have a LOT of above grade ICF using the biggest vs the lowest of those numbers won't change the whole-house number by very much.

R10 under the slab would be essentially zero heat loss if the slab wasn't heated, but it'll be some thing when used as a radiant slab. Precision isn't very good due to the variable conductivity of soil type and distance to the ground table, seasonal ground moisture and the slab temperature when it's heating the house at max load all make a difference. But it'll still be at most 10% of the heat loss of the rest of the house at design conditions.

Using a design temp fully 8F below the published ASHRAE/ACCA design temp and using 72F as an indoor design temp rather than 68F (which is pretty damned comfortable in a radiant-heating house) is malpractice. Using -7/+68 is a 75F delta-T, whereas using -15/+72 for the 87F delta-T, increasing the minimum size of the heating plant by 16%. I they do similar cheats elsewhere it's pretty easy to come up with 30-50% oversizing, not even counting the inherent 15%+ safety factors built into heat loss calculators.

At the upfront cost of geo, putting the thumb on the heat load scale practically criminal, adding thousands in unnecessary cost. Geo runs about $9K/ton in my neighborhood (sometimes more). If Manual-J done completely above-board, without any skewed inputs says 3 tons, odds are pretty good that even a 2.5 ton system would keep up. But with CYA factors adding 20-50% to the Manual-J, and they end up designing & installing 3.5-4 tons for what is actually a ~2.5 ton load it's more than 10 grand in unnecessary cost. It's bad enough when adding that much CYA upsizing to a condensing gas furnace, but it's financial abuse to upsize geo that way. If you can't find heating contractors who won't fudge the numbers, it's worth paying a competent third party energy-consulting (not HVAC) contractor to run accurate heat load numbers for you, even if it costs you several hundred (which it might, if they run a blower door test for higher accuracy.) It doesn't usually make sense to take it that far for sizing gas-fired heating, but it sure does with geo.

I don't know the size of your house but if Dana says 2-3 ton, AND you already have a boiler for the basement, AND cost is an issue, use the boiler (unless it is propane or oil). Put the floor heating in upstairs, with a gypsum cement overpour and call it a day. I am sure your boiler has the capability to handle the heat loss , especially if it is a condensing boiler.

If the boiler is oil or propane, switch to an ASHP that heats water....yes they are available and will have an electric element as backup. We make them as do some others. With your electrical rates, you will be laughing.

In an all-electric house, it's an electric boiler, so some form of heat pump is called for even though her electricity rates are well below the national average ($0.046/kwh is about 1/4 what I'm paying), but if only the basement zone is on the boiler, it would be very difficult financial argument to make. The whole house running on one heat pump has a better rationale.

Unlike in Europe where there are at least a dozen vendors to choose from, tere are very few ASHPs with hydronic output available in the US. The Daikin Altherma series is the only one with any number of installations, and it's still a very low number indeed, and the output a the design temp of -7F/-22C is limited. But NRT.Rob (who is doing her radiant design) has first-hand experience with that series in a similar winter climate, and would be better able to advise once valid heat load numbers are calculated.

I wouldn't make the call prior to doing the careful heat load analysis as well as the financial analysis. Places in IA with design temps of -7F usually have an average January temp of about +20F/-7C , so even pretty-good ASHPs would be only making seasonal average COP of ~2.5 and possibly less, unless the whole heating system can be run at a very low temperature (not just the basement zone. If it runs out of capacity at even 0F relative to what a careful heat load calc says it wouldn't be a good way to go. A GSHP installation is likely to average ~3.5 for a seasonal COP, can be designed to carry bigger heat loads, and has substantial subsidies available, whereas hydronic ASHP solutions do not, SFAIK. But if the radiant can be run at a low enough temp it's conceivable that the Altherma might average close to 3, and at 4.6 cents/kwh it may take forever to make up the cost difference in higher efficiency.

It may still be more cost effective to go with GSHP, but it's worth doing the math on the difference in final installed costs would be, and how much (also subsidized) photovoltaics that might buy, and whether the PV would more than make up the difference in seasonal power use between the ASHP & GSHP systems. At those very low power rates what's a no-brainer in my neighborhood would require a more careful look for her.

But it all starts with a better heat load calculation, since that determines the size & cost of the radiation (if all-hydronic) and the heat pumps.

I must have missed the "all electric" part. Of course a proper heat load is called for first. There are some other questions such as ....is solar thermal desired or PV. It would take a semi-custom HP but solar thermal could be added.

is the total cost of the electricity including all the transportation charges in everything else as a part of the bill is it your total kilowatt hours divided into the total dollars of the lower right corner of the bill ? or are you just going by that rate number in the middle after that 101 customers I have helped with rates found we have to divide by the total bill not go by the riate number then we even found air source heat pumps better and condensing gas was very close to inappropriately installed geothermal

There are places in the upper Midwest where the whole delivered cost of electricity at residential rates are 7 cents or less, as hard as that is to fathom here in 15-22 cents/kwh land. The residential retail average in the state of Iowa is ~7 cents/kwh, with local markets within the state where it's less. Off-peak rates under a nickel are the norm.

In IA the moderating effect of the large installed base (and growing) share of wind power seems to be flatting out average rates and limiting price inflation. Since the marginal cost of wind is about 1 cent/kwh it can always under-bid fossil plants whenever the resource is available. Wind is currently delivering about 20% of the total annual supply for the state, and is cutting into the capacity-factor (time fraction at full output) of local fossil grid sources. Those plants can't compete on price even if the fuel were free, due to higher maintenance costs per kwh. The installation cost of wind per peak megawatt is high (but falling), but once it's up, the marginal cost of power is near-zero.

Electricity is likely to remain cheap in IA for some time to come, but that's not to say it makes heat pumps uneconomic, just not the slam dunk they are in my neighborhood.

Wow! Great discussion. Thanks.

Joe - it's the reason I very much want 3rd party heat loads. Just today we visited with a general, and I said based on some rough numbers we could be looking at a 3 ton unit. He said he would not put in anything less than a 4 ton in because our house is so big, and we may be needing a 5 ton! I asked if his HVAC guys did heat loads, and he said that he always asks for an extra well/ton more than what he gets quoted to be safe! Then I explained what my ideas were on insulation, and he said no need for all of that, a simple BIB in fiberglass in a 2x6 is more than enough and wasting money on asking for anything else, and then I feel like an idiot for asking things that he wasn't even interested in even entertaining.

Dana1 - 4 years ago I tried to find a framer to do OVE, no one knew what that was, and no one would bid me framing with flimsy 24 o.c. the two willing to try it upcharged so much vs. normal that I could not afford it. I did my best to encourage less studs, but we still ended up with more than needed. At least I did convince our framer to do the corners like in the OVE details, and to ladder interior walls to increase some insulation space. Since I get stuck on small details, i will probably count each stud and rough how much sq. ft. of wall space I have in framing. If I had unlimited resources, i'd be buying those thermabloc strips made with aerogels to cut the thermal bridging even more. I got a sample from the manuf, and it's pretty cool! I'll keep scratching the lotto and maybe I'll win enough to afford those.

I will get heat loads done by a third party, but not until we finalize our loan and we are sure we are going forth! One of the hvac subs we priced said he uses 7th edition manual j and should be good enough for sizing. Then said if I want Manual S and D, I have to hire someone else since they don't, which I think is the norm around here.

On the ICF wall, I've used R24 in the past, vs the R28 claimed by the manufacturer. The exterior perimeter is roughly 206 ft, with 65 ft of that being completely above grade, and another 54 ft of basement wall the ground slopes upward. So there is quite a bit exposed, and it's more of a second floor, than a basement.

Your comments about the design conditions I've been told they use, and even with my primitive/basic understanding of the importance of proper heat loads, I am very concerned that I'm getting bids for systems that are oversized. But I'm getting really tired and feel like it's such an uphill climb to get things right. The one HVAC I thought was a winner, let is slip during a conversation that his software can't even go above R13 for walls, and R38 for ceilings so I'm not as confident now on his estimatet. And if as you say they fudge here and there, what am I truly getting vs. what I should get?

Mike - We have about 3850 sq ft. Our electric boiler is sized for the whole house, and budget is an issue. My dream home would have radiant heat everywhere, but then again, I can't get anyone local to bid anything above a 1 zone system without me having to go rob a bank to be able to pay them. It's the reason NRT designed our job in the first place 4 years ago. The compromise back then when budget ran out was to go ASHP forced air main floor and cool, and leave the basement with radiant. We're blessed that we're in a better position now that we can look at finishing the house all at once, but budget is still an issue. The time to visit about adding GSHP would be now, ideally to replace the boiler, add radiant in the main floor, and cool with forced air. But that's the cadillac, and I'm sure that if we have to pick between radiant vs. finishing the house, the radiant will not make it, and we'll get the chevy. But I do want to make sure that a GSHP is worth the extra $ vs an ASHP. Again, without proper loads it's all a guessing game right now.

Dana1, Rob at NRT talked about the Daikin ASHP to run a whole house radiant scenario (since I'm still very much exploring that option), but there a no local vendors/installers near me, not even in the whole State that I could find. When they did the initial heat loads 4 years ago, the max design temps were 115 for the whole house radiant option.

KnotET - on the heat rates the delivery fee is only $5/mo plus other fees is about another $8 so my $.05 rate is more like $0.06 on avg, but that's only for heating/cooling (via dedicated separate meter). Regular rates for non hvac needs are more in the $0.11 range.

I hadn't considered PV, since I have never heard of anyone in the area that does them, let alone seen a house with them. That usually means the one or two local vendors that do them probably charge a lot more since it's special market. But now I'm wondering if anyone does install them, and that I should get an estimate. Might be worth it (or add it to the future list along with adding a wind turbine to our small property to supplement, then switching to a wood fired outdoor furnace, and even a small hydro turbine in our river and getting off the grid). I'll keep scratching tickets.

Posted By Boontucky-girl on 21 May 2012 11:46 PM
Wow! Great discussion. Thanks.

 
Mike - We have about 3850 sq ft. Our electric boiler is sized for the whole house, and budget is an issue. My dream home would have radiant heat everywhere, but then again, I can't get anyone local to bid anything above a 1 zone system without me having to go rob a bank to be able to pay them. It's the reason NRT designed our job in the first place 4 years ago. The compromise back then when budget ran out was to go ASHP forced air main floor and cool, and leave the basement with radiant. We're blessed that we're in a better position now that we can look at finishing the house all at once, but budget is still an issue. The time to visit about adding GSHP would be now, ideally to replace the boiler, add radiant in the main floor, and cool with forced air. But that's the cadillac, and I'm sure that if we have to pick between radiant vs. finishing the house, the radiant will not make it, and we'll get the chevy. But I do want to make sure that a GSHP is worth the extra $ vs an ASHP. Again, without proper loads it's all a guessing game right now.

Dana1, Rob at NRT talked about the Daikin ASHP to run a whole house radiant scenario (since I'm still very much exploring that option), but there a no local vendors/installers near me, not even in the whole State that I could find. When they did the initial heat loads 4 years ago, the max design temps were 115 for the whole house radiant option.

I hadn't considered PV, since I have never heard of anyone in the area that does them, let alone seen a house with them. That usually means the one or two local vendors that do them probably charge a lot more since it's special market. But now I'm wondering if anyone does install them, and that I should get an estimate. Might be worth it (or add it to the future list along with adding a wind turbine to our small property to supplement, then switching to a wood fired outdoor furnace, and even a small hydro turbine in our river and getting off the grid). I'll keep scratching tickets.

For floor heating, the most economical system is a single zone per floor. I like it because i find people set and forget the t-stats (which I stopped using a few years ago, for the most part I use just outdoor temps) and if the there is a lot of south side solar gain on a thermal mass floor, the heat can be moved to the cooler areas.

Personally, being on a budget, I would forgo the GSHP for a ASHP because, it is hard to retrofit a thermal mass floor after the fact but a HP can be upgraded. As far as the temps for the floor, 90F is doable with the right amount of tubing in the floor., given your attention to heat losses.

I wish our solar thermal/ASHP was ready but, alas, another year for that.

But if there isn't a vendor support or an installer of hydronic-output ASHPs within 100 miles of her, that option may be off the table at any price. A wood fired boiler may be viable though.

Thanks Mike. My problem wasn't really that normally they do single zone radiant installs in my area, my problem was that no one knew/was able to give me what I wanted, which was multi-zone radiant. And those who gave me estimates were so high it was ridiculous, and some of the answers were quite outrageous (like I needed double the tonnage in a system to handle hydronic because it was harder to get the heat to the water, or that I needed a pump per zone, etc. etc.)

I'm not quite sure I understand what you mean by upgrading thermal mass floor?
At the rates things are going, maybe next year we'll be ready to actually get our building going, and you get your distribution center here in IA and I'll try your system.

Dana1 - I do have enough timber in my acreage that maybe I should be looking at a wood fired boiler. If only they had auto-refill so I wouldn't have to go out to replenish the wood, that's be great. Not to mention the difference in amount of labor to keep a good stockpile of logs for heating, vs. wood pile for fireplace only. If this house ever gets done, maybe I'd have plenty of time to do that.

I got a copy of some heat loads that I got from one of the HVAC guys we're estimating. couple of questions, in the cost analysis provided, they have DHW compared between having a geo system and ASHP. Does that mean they are comparing the cost of the GSHP to run to produce some of hot water, vs. running our electric water heater to do full DHW needs?
So if they say with the ASHP the DHW cost is X, but with the geo is Y and the geo is handling 60%, does that mean then that the other 40% DHW load is still handled by the hot water heater? So to compare, DHW cost with ASHP is X, vs. Y+.4X for the GSHP? Or am I reading this wrong?

They also have the electric rate for heating with the GSHP at the correct rate, but the ASHP rate is twice as much. That doesn't make sense to me, since the electric rate is the same regardless of what system I use. I would assume the difference should be the KWH to run the GSHP to meet our load, vs the KWH to run the ASHP to meet our load. I also noticed the winter peak electrical demand is different for both systems (ASHP higher than geo) Is this right? This seems like an input parameter, so why would they be different between systems?
Just trying to learn more so I can read these cost comparisons right. Thanks.

Posted By Boontucky-girl on 22 May 2012 11:56 PM


They also have the electric rate for heating with the GSHP at the correct rate, but the ASHP rate is twice as much. That doesn't make sense to me, since the electric rate is the same regardless of what system I use.

sounds like they are skewing the numbers in favor of geo.

The difference between multi zone and single zone from technology perspective can as simple as putting "telestats" on each loop of the manifold (which i don't like much), to create control for each loop, or having separate piping to each manifold (zone) with its own pump in the basement (I prefer this system because you design the zone as well as possible and the fluid flow matches the needs of the zone)

Telestats are powered valves that are tied to a thermostat so there is one pump whose flow is high when all the loops are open or lower when some ore open. It is not as controllable as separate pumps and supply piping.

This can account for a considerable cost difference and honestly, from a running cost point of view, there is not much difference. Many people say they want to control their zones differently but it rarely happens.

By upgrading to a thermal mass floor, I mean that if you did do forced air upstairs and had all your floor covering down, taking them up again would be expensive and a PITA. To me, planning it in, with tubing, from the beginning is the best choice.

Most North american heat pumps heat the water with a "desuperheater" which means that they can take some heat off the compressor while it is running. Using this method only produces X amount of heat and the balance must be provided by the backup heater. They are saying the HP will provide X times .6 for one method and X times .4 for the other (X being the if the DHW was heated entirely by electric resistance).

The way we designed our HP (air or geo), the primary DHW is done by solar (usually around 60% annually) and the balance is provided by the HP. Only on rare occasions is the electric immersion element doing any work. To me there is no point in running a HP in the summer if there is no cooling to be done and if there is cooling, we use all the heat taken out of the air and put it into the DHW (assuming it is needed) before dumping excess outside.

I understand the issues with the utilities. They have been told that Geo is the best thing going and because the drop in electrical usage is so high from a utility point of view, they should support it with a cost reduction. The issue is that ASHPs and don't get the press that GSHPs have so the utility doesn't put them in the same boat. For the utility, it is all about not having to import expensive peak power which is quite costly. Perhaps if an argument was made that an ASHP was still much more cost effective than straight electrical they might let them in on the savings. Who knows, but I don't see an ASHP lobby anywhere.

It is true that the ASHP will use more power than the GSHP on the coldest days but on other days it uses less. We tend to look at costs on an annual basis but utilities look at peak costs.

Posted By geodean on 23 May 2012 08:00 AM

Posted By Boontucky-girl on 22 May 2012 11:56 PM


They also have the electric rate for heating with the GSHP at the correct rate, but the ASHP rate is twice as much. That doesn't make sense to me, since the electric rate is the same regardless of what system I use.

sounds like they are skewing the numbers in favor of geo.

In my AO one company offers electric heating discount for geo, but not all ASHPs qualify.

Posted By joe.ami on 23 May 2012 09:13 AM

Posted By geodean on 23 May 2012 08:00 AM

Posted By Boontucky-girl on 22 May 2012 11:56 PM


They also have the electric rate for heating with the GSHP at the correct rate, but the ASHP rate is twice as much. That doesn't make sense to me, since the electric rate is the same regardless of what system I use.

sounds like they are skewing the numbers in favor of geo.

In my AO one company offers electric heating discount for geo, but not all ASHPs qualify.

"since the electric rate is the same regardless of what system I use."   This is what   I was basing my comments on .

Thanks Geodean. That is my concern. The rate used was 4 cents on the geo, and 8 cents on the ashp. I'll see if I can decipher what they estimate for annual KWH of the ASHP and do the math. If that is true that they are skewing numbers one way vs. the other, it make it harder to trust what they say.

Mike,

Yes, I knew to run both methods are about the same, but the installation costs of one vs. the other was very different. those weren't the only things. I'm not an expert but even I know some things make a difference, like loop spacing, heat loads, flow rates, floor sensors, etc.

Oh, I see what you mean by thermal mass floor. I don't have double bottom plates, and not sure I want gypcrete in the main floor. Not sure either if my floor would hold the weight of lightweight concrete either, specially with tile. i'd love to have stone, but my joists are just slightly above L/480 for the areas where tile is planned. Not to mention that if we do go with granite counter tops, specially on the island, I'd be concerned about deflection and tile cracking with adding concrete weight. I should probably check the load added by extra 3/4" of plywood sleepers all over if we get the radiant upstairs installed.

The quote we got was to install geothermal with a bosh unit, and the cost comparison to the ASHP only says ASHP SEER 16, no model number, brand, or anything... so I can't even google it.
So when it says winter peak electrical demand, that means the geo will pull so many KWH at the peak demand times vs. so many KWH for the ASHP?

Posted By Boontucky-girl on 23 May 2012 06:40 PM
Thanks Geodean. That is my concern. The rate used was 4 cents on the geo, and 8 cents on the ashp. I'll see if I can decipher what they estimate for annual KWH of the ASHP and do the math. If that is true that they are skewing numbers one way vs. the other, it make it harder to trust what they say.

Mike,

Yes, I knew to run both methods are about the same, but the installation costs of one vs. the other was very different. those weren't the only things. I'm not an expert but even I know some things make a difference, like loop spacing, heat loads, flow rates, floor sensors, etc.

Oh, I see what you mean by thermal mass floor. I don't have double bottom plates, and not sure I want gypcrete in the main floor. Not sure either if my floor would hold the weight of lightweight concrete either, specially with tile. i'd love to have stone, but my joists are just slightly above L/480 for the areas where tile is planned. Not to mention that if we do go with granite counter tops, specially on the island, I'd be concerned about deflection and tile cracking with adding concrete weight. I should probably check the load added by extra 3/4" of plywood sleepers all over if we get the radiant upstairs installed.

The quote we got was to install geothermal with a bosh unit, and the cost comparison to the ASHP only says ASHP SEER 16, no model number, brand, or anything... so I can't even google it.
So when it says winter peak electrical demand, that means the geo will pull so many KWH at the peak demand times vs. so many KWH for the ASHP?

It does make ASHP hard to install when they skew the pricing like that. I would call them and ask what the requirements are.

Regardless of what heating system is installed, a closer tube spacing will result in a lower water temp and a better economy. The difference in cost might be 30-35% to go from an 8" spacing to a 5" spacing but the floor will have a more even temp. The problem is that most of the plywood/aluminum plate systems are fixed at 8" or maybe 6" spacing so you take what you can get.

Gypsum cement is supposed to fall within the code requirements without beefing up the joists but each home is different and needs to be looked at individually. IIRC gypcrete is about 14lb/ft2 @1.5".

The bosch is a relabeled Florida Heat Pump and although I have no personal experience with them I am told they are a reasonable unit. 

Joe - my electric co-op offers the seasonal rates for anything HVAC, I could even go with regular electric baseboard heat and outdoor A/C and get the rates. Currently there are no restrictions on one equipment vs. another type. They do limit it only to HVAC equipment. The rebates for installing equipment are slightly better for geo, but not much.

Mike - I'm not too stuck on any particular brand right now, and I haven't seen much for reviews where the complaints are because of a particular equipment. Most of them seem to be about the install/installer. I'm trying to find the right contractor who has good reputation, quality, and service and then consider the brand of equipment they use. But at the same time I do want the right equipment for our needs, which was part of my original question.

The dry sandwich I want for the main floor could be done to whatever spacing. I think for the most part 8" is typical so you don't waste too much plywood when cutting the strips. Closer spacing does mean higher cost in labor, plus additional pipe and I would think that affects loop design.

I have the load rating tables for my joists, so I can look up the load rating for the unsupported spans where tile will go, and add the weight of different assemblies. I'm sure it's on the to-do list somewhere.

Thanks.

Forgot to comment that I do plan to call the HVAC contractor and ask questions about the loads they gave me. The rate difference is one of them. Good point on what different electric companies may allow, since this particular company is probably used to dealing with the neighboring utility company, since that is probably their primary market. They could have different rates based on equipment, compared to mine.

Thanks.

If available in your area, consider shopping for electric suppliers.

Consolidating for a cleaner response about any rate data:

Supplier choices are all going to be deregulated by 2015, already in nearly 10 states, residentially; and 16 and DC now for commercial.  www.chooseutility.com  for example, one group handles 8 or so electric suppliers and in OH to NY to CA, etc. IGS gas and Dominion gas SELL ELECTRICITY , and their territories are on the net .

Still it can be seen today, among claims of an all electric "same rate", - there still are some communities receiving 'penalties' for the required supplemental heating spikes in kwh/ even if just a few hours of spiking with straight electric strip "KW-heaters-back-up". Customers still can be found under 12 cent rates averaging compared to HtP+ Electric supplements averaging over [then] $.14 .
[for some ] -that may drop a '2.5 COP' annual utilization averaging to much closer to 2.2 COPerformance in some -5F below zero in - - - 'gotta have a 68-70-deg home' consideration of then what I simplify as $COP's to $COP's out o' pocket(s).

Which gt?
originally asked-  ? 
You may also find yourself just asking about some more 30 year old proven heat-reclaiming HW heating WHILE in cooling modes for your hot water production. A method of adding a Water:Water GT in with a W:Air has been done - but ask  like, 2 units or 1, and while in cooling, and How many $$ ?
What percentage is reclaimed annually? is a great question/ with what maintenance- SAVINGS that can reasonably be calculated can lead to that  higher gross dollar ROI and 6:1 to 15:1 value added to a home (if real valued equity allows) for each dollar saved in a year  , I have reason to believe.

Other Solar sites put it at 20:1

"That is to say, if a solar system can reduce the electric bill by $1,000 per year, the home is worth about $20,000 more in increased appraisable value. The rational is that if the $1,000 is not spent on electricity, it is available to be spent on a larger mortgage payment [about] ...Risk vs. Reward."

I am not too far from you, in north east Iowa. Here we have a few different power companies, and most offer geo intentives far greater then ASHP incentives or gas furnaces. Some offer reduced rates as well. My power company supplying our new home to build has options that actually make geo cheaper to by then a typical 16 SEER ASHP when combined with the feds credit. Make sure to check into other rebates and discounts your power company offers. Ours has a "new home" package that has several tiers. If you build a home that is 5% better then ES for example, you get 5k in rebates plus a geo rebate which is based on a forumla. With our sized 2 ton system, it would be about 3800 rebate on the geo. This brings the price below a furnace or ASHP quotes including the 30% credit. loads for our 3k sqft house (half below grade) is just over 2 tons total, so we will go with a 2 ton system (vertical closed wells) and 7 kw strip backup.

Where I am I get one choice for electric company. The coop offers $350/ton on geo, and $150/ton on ASHP + $250 for the unit. So the geo is a little better on the coop incentive, but it's still higher in install cost vs. an ASHP. It would be nice to have $3800 on rebates from the local utility. I can get an additional $500 if I have the house professionaly hers rated and is above min. energy star requirements. But not sure how much the hers rating costs around here. So really on the incentinves I don't get much more to push geo vs ASHP when counting the tax credit.

Thanks

I finally found one HVAC contr. that does do full manual J! I got quoted a 4 ton unit for my 3800 sq ft house, but contractor did say he doesn't do the full loads unless he gets the job, which i totally understand. I doubt dropping down to a 3 ton unit will be that much savings up front, and not sure how much of a difference in operating costs it is to go from a 4 ton to 3 ton to justify the higher insulation expense (if the loads were to come out that 3 ton was big enough).

I have a question, does adding an extra loop to a geo unit mean it's better? For example a 4 ton unit with 5 loops? 3 ton unit with 4 loops? I have one hvac contractor insisting that it's good insurance and better. True or false?

Another one said (without any heat loads, mind you) that there's no way anything less than a 4 ton would be adequate for my house because of the amount of air that needs to be pushed to the extreme ends of the house (mech room is in the middle). Does that make sense? And that he balances the unit to 0 degrees. What does that mean?

Thanks.

The difference in operating cost is nothing compared to the difference in upfront cost. If the 3 ton is slightly undersized at the heating design temp it means the operating cost would be slightly higher if resistance electricity is used to make up the difference, but that's usually a small adder to the operating cost (especially in cheap-electricity land.)

In my neck of the woods GSHP runs about $8-9000/ton. Dropping from 4 to 3 tons of GSHP would likely yield substantial savings, saving that would take DECADES of auxilliary power use on a slightly undersized system to make up. But clearly YMMV.

At 4 tons for a 3800' house it feels like a "1000'/ton" sizing rule of thumb for cooling, which is usually about right for newer-better construction. But with R60+ attics and way-better-than-code windows even that can rule of thumb can yield substantial oversizing.

Paying for the Manual-J up front will usually save more than any fee charged for that service just in well-drilling & loop sizing if it shrinks the design by a half ton or more from a WAG or rule-of-thumb approach to sizing.

It is uttter nonsense, complete balderdash, that an extra ton of capacity is needed for the sole purpose of pushing air to ends of the house. If needed, a 2 ton system can push every bit of its airflow to a room 100' away if the Manual J calls for it. That's not ideal, but it is doable. It simply takes a bit of attention to duct design, test and balance.

I hesitate to mention this, but some brands allow 3 ton systems to be ordered with a more powerful blower, the same blower standard with 4 tons and up. The reason I hesitate is that option is yet another crutch for poor duct design. The only time that option is acceptable is when existing ducts or building assemblies housing ducts do not allow the ducts to be properly sized.

I concur with Dana. The best ton of the capacity is the one not needed, bought, installed or operated for the life of the building. An investment in insulation or upgraded windows that staves off an extra ton of geo pays off up front and down the road.

If possible, pay for the Man J calc up front with the understanding that the payment will be credited toward the system if purchased. You want a room-by-room Man J, not just a block load. The room by room result will drive duct design. Once the Man J is done, (assuming it is computerized) substitutions can be quickly made to guage the effect of various insulation options.

I've gotten 3 bids for geo, 4 ton Hydron modules between 22K and 24K before credits. These are combo units that would do forced air upstairs and replace electric boiler for radiant in the basement. I asked one what would it be to go to 3 ton if heat loads show 4 ton is oversized, and they said be $1700 less.

Hard to justify to spend an extra $6K on insulation to save $1700! Even to justify a payback of 5 yrs on extra $$ for insulation, we'd have to save $70/mo on a 3 ton compared to the 4 ton, and I doubt that would happen. I feel like we should stick to the $8K bid for an ASHP, leave the bsmt radiant on the electric boiler and save the extra $16K for geo. Very disappointed right now.

If you need to see a 5 year payback to invest in anything, note that in that time frame you can't even make a financial argument for code minimum insulation levels, let alone a ground source heat pump. Just the cost of going code-min won't usually show a positive net-present-value under 2 decades without significant (possibly unrealistic) energy price inflation &/or unrealistic discount rates.

Can you point to an investment of ANY type breaks even (after taxes!) in 5 years? That's about a 15% annualized after-tax return!

Got junk-bonds? No, those are only paying in the 7-8% range (and that in pre-tax dollars)... lessee... hmmm...

How's about mortgage-default-swap derivatives?

The lifecycle of insulation is long at least 4-5x longer than a GSHP, but if you insist on short-term (or fully up-front) payback none of it makes sense. To make rational decisions you need to do the full financial analyses and compare lifecycle costs. If you don't plan to hang around in this place for another couple of decades the numbers probably not going to work for you unless you anticipate very high energy-cost inflation in your local market. At some point the cost of energy saved by insulation becomes more expensive than the lifecycle cost of photovoltatics & air-source heat pumps (even at today's prices & efficiencies, let alone what the PV cost & heat pump efficiencies may be in 25 years, well within the lifecycle of insulation), which is a growing criticism of the PassiveHouse approach.

Even the smallest bare-bones GSHP system has a minimum cost independent of tonnage, (be it $8K or $20K): Any system has to be designed, plumbed, wired, & drilled/dug, and some of those cost barely change with system size. In my neighborhood I suspect drilling is the lion's share of cost, and drilling through granite comes at a substantial per-ton premium. But clearly YMMV.

Even though your total system costs for GSHP are much lower than mine (by a third) for equivalent systems, your power costs are also less than half mine, so from a strictly financial point of view you're right, the lower cost ASHP system is likely to have a lower total lifecycle cost than a GSHP system (even after the GSHP subsidy). Even though the ASHP may use 50% more power, if power is cheap it never catches up. In a 5 year time frame that would ABSOLUTELY be the case.

With insulation and high-performance windows you're paying as much for comfort as you are for energy use. When it's 0F outside the difference between a code-min wall and an R20+ (whole-wall) is something you can easily feel, since the temp of the interior wall is significantly higher on the high-R wall, making for a higher average radiant temperature. It's harder to tell the difference between R20 & R40 walls, but still possible. The comfort difference between U0.30 windows and U0.20 windows is even more striking (but so is the price, eh? ;-) )

Hi Dana1 - yes, you are right in up front/short term payback is hard to rationally compare the payback. But even at 10 yrs, still hard to say let's spend $6K more to save $1700 up front. I do believe that comfort is worth it, but when the budget gets slashed in half because the house didn't appraise as expected, it's very tough. And I'm talking just numbers. I just feel like I keep hitting my head on a brick wall and very frustrated.

Yes, .3 windows were definitely more expensive... but when we installed them we really believed the house would appraise high enough to justify it and cover the expense of them. Appraisal was horrible. Will cost more to build than we can sell for. So to finish the house with the higher insulation, all radiant heat, and decent flooring/trim we couldn't even turn around and sell it. Can't even get a loan to pay for what it will cost to finish. So in my case I don't really have much to help me push insulation costs since that goes behind the wall and avg. homebuyer wouldn't care. They'd care about utility bills but with GSHP and cheap rates higher insulation won't make that much of a difference on that. Not that I'm planning on selling. We wanted to build our dream home and stay here till we retire. But not sure how to get higher insulation fit in the budget when we have the not dream budget.

But not sure how to get higher insulation fit in the budget when we have the not dream budget.

Less house.

While building a home you only get one shot at the energy details. Other amenities can be added later. We built in 2007 and faced budget issues. We chose to give up a metal roof and hardwood floors (figured we could have them later) in order to keep sprayfoam, good windows, and geo.

Less house is a fair point. We are students of the "not so big house" way of thinking - no formal dining room, minimize bedroom sizes, reasonable ceiling heights.

Why not upgrade insulation and go ASHP?

Posted By joe.ami on 08 Sep 2012 06:29 AM
Why not upgrade insulation and go ASHP?

Into kicking over hornet's nests, are we?

In the land of cheap electricity, that's probably a reasonable thing to do in the face of the declining home valuation. The marginal upfront cost (even subsidized), for the GSHP system may have less of a financial rationale than the ASHP + electric boiler solution if you're paying 7 cents/kwh rather than 20 cents/kwh. The lifecycle of the insulation is 5x that of a heating system, and the performance difference between ASHP &  GSHP may never "pay off" over the life of the equipment if electricity stays cheap. 

Insulation is boring and lo-tech, highest-efficiency heating equipment is more exciting, but none of it changes the resale value of the house very much (not that you're selling). Insulation & better-class windows buy more comfort than higher efficiency heating systems do, at equivalent power use & interior temperatures.

In the unlikely event that electricity prices somehow triple during your tenure, making running the radiant floor in the basement with the electric boiler prohibitive, you can always do the math on heating that zone with a mini-split which would cut the power use on that zone by well over half, but giving up the cozy toes barefoot cush factor when it's below 0F outside.

ICFHybrid - yes, less house would be a reasonable choice. My problem is that my house is already framed, sided and shingled so can't do anything about reducing square footage at this point. The interior is just not finished.

Engineer - I totally agree! But the appraisal was based on certain specs (tiled floors, granite countertops, trim pck, solid wood doors and cabinets, etc). We had 2 appraisals, one cost to build, one retail value. Cost to build was higher than what I can sell it for because of comps. My problem is I can't downgrade the pretty too much because then the house will be worth even less which means even less money on the bank to finish it. When geo will take 24K in one swipe off my dwindling budget, it sucks. Not so big house is not an option at this point. I got the big house, I want to finish it.

Joe - Iowa now has a new tax credit of 20% off the 30% fed, plus utility rebates it looks like we're down to $12,500 K on the geo vs. 8K for the ASHP. It was the main reason we considered adding it now since it got so close. But at that time we thought for sure the house would appraise for what it would cost to build from scratch today!

Dana1 - my concern is that insulation I can't upgrade and whatever we end up for HVAC equipment won't get upgraded either. Once the walls are closed I can't go back!

Optimizing for appraisal value and for energy use are conflicting goals. But it might help to put things into two lists - things that can be improved later and things that can't. Resistance heat and window air conditioners are probably disposable.

What's the estimated annual operating cost of the ASHP vs. the GSHP?  

Earlier you made the comment "...even at 10 yrs, still hard to say let's spend $6K more to save $1700 up front."

With geo vs. ASHP you're looking at spending another $4.5K up front to save what?  It's a similar magnitude of investment.

Unless the geo costs $450/year less to run than the ASHP, the 10 year simple-return financial analysis fails, and in another 10 you'd be looking at major component swap-outs looming.  I suspect the operating cost delta is going to be less than that unless you cranked the temp in the basement way up and burn a lot of power with the electric boiler.  It'll probably be at least $150/year savings (which take 30 years to pay out in simple terms), but probably less than $300 (which would be a 15 year payout-simple.)  But that's just a WAG. If it were MY house I'd model the energy use with BeOpt and work backwards from the anticipated COPs of the equipment to come up with a realistic kwh/year delta, converting that to $/year delta.

And I'd do the same for the insulation game:

If the extra $6K in insulation knocks off $1700 off up front (assume it knocks off $0 up front for the ASHP) and say, $150/year off the operating cost, in 10 years it still hasn't broken-even.

But with modest price inflation assumptions it will have paid off in 25 years, and will still be going strong for another 50+, no maintenance required. To get $150/year savings out of $6K in insulation once you're at code min means you have to insulate wisely- R100 attics don't make sense with ~R20 (whole-wall) walls, but R60 probably does in the long term (maybe only R50, if GSHP.)

The thermal performance of the wall was baked into the cake the day the siding went up- whether you go with all dense-packed fiberglass vs. an all closed cell foam fill makes less than a 10% difference in whole-wall R.  Whether you spend a little or spend a lot, there's not much further savings to be made there, so spend a little, keeping the long term in mind. (Were to do it over again, 2" of rigid  iso on the outside and 5.5" of fiberglass in the cavities likely would have come in at lower cost w/higher performance, but with the siding up that ship has long since sailed, time to move on.)

It's now only a matter of how cheaply can you protect the sheathing from wintertime moisture drives, since there isn't sufficient exterior R to provide that function with an all-fiberglass fill.  It would be safest to go with 2" of closed cell and no interior vapor retarder, but you're still in great shape with a sloppy 1"  flash-foam + fiberglass, no interior vapor retarder solution.  At a buck a board-foot putting more cc foam into stud bays than is necessary to protect the sheathing is a lousy investment-  a 1" shot of interior foam buys a lot of resiliance for the assembly that just can't be had with strong interior side vapor retarders. (Which is why the blowing mesh needs to be a high-permeance type, which is most of them.)  It's half the foam, 25-30% more fiberglass (material, not cost)- keep the mid-winter indoors RH at or under 30-35% (not 40%+) and it'll be fine. 

In the attic you can just air-seal the seams & penetrations with foam, not a full coverage flash, then shoot R50 cellulose and defer going higher-R for now. Unlike walls, you CAN go higher later in attics.   If the inspectors require a stronger vapor retarder, use a barrier-latex primer on the ceiling- it's a heluva lot cheaper than a 1" shot of foam, in a location that matters less than in wall assembly.  Low density cellulose WILL settle a bit in 10-15 years in an IA climate, but it'll pretty much stop there.  If you blow in 16-18" now it'll start out at R55-60, settling to 14-15" and ~R50 in 10-15 years.

Yes, to question value of more insulation vs. value of more cash for geo is the same argument. One difference is that the appraisal showed that the comps similar to my house without geo the difference in value in my area is about $5K more for houses with geo vs those without. So with tax credits getting the difference between ASHP and Geo to within 4 grand almost seemed like that investment would pay for itself, IF we had a need to sell the house. Plus geo is all the hype here now. Last two home shows 95% of houses in the parade praised the fact that theirs had geo. And the cheap bills!

The only calculation that I have been able to get comparing my boiler/ASHP vs geo operating cost did show huge difference in operating costs. But looking at the numbers I saw that the electric rate used for the ASHP/boiler was twice that of the one used for geo. Maybe it was a mistake, maybe not. But hard to trust it. The general that used this company was way more than we could afford so we did not continue to talk with them. So I don't know for sure what the difference in operating cost is of one vs. the other for my house.

I've asked the hvac company we want to hire if they will consider us prepaying for the heat loads/cost analysis then credit once we purchase equipment. Have not heard back, so we'll see.

I agree that with siding up, I have no choice but to make the best I can in the interior for insulation. And your comment that insulation will be going strong 50+ years is why I want to get it right now. If I can afford the best insulation stack up, that's what I want to do now.

I know with time I can air seal just as good with foam, but I don't have the time, not when we're getting a loan and having a contractor run the project. If we were still self financed I would not be trying to figure it out since we'd just save the money to pay for what we want. But that's not an option anymore for all sorts of reasons.

Also in the attic, the spray foam is not just for air sealing. I do have concern for the edges of the attic where I can't get 16" of cellulose, specially right over the double top plate. The foam would help max r value in these areas. Plus I would think that even a sloppy flash would cover better than one guy crunched up in the attic foam sealing things. One could cut up blue board and foam glue it for the same effect, but then again, no time to do a good job, no money to hire the labor for it.

My area has not adopted code yet so technically where I live, code is R0 since no one will come out to inspect it. The city nearby has R13, R38 in attic. I've given up trying to get R100 installed now. I'm having a hard time convincing insulators that R50 is needed without them turning around and bidding high since they never done that. And since apparently no one has done flash and fill around here, they are concerned about moisture and mold. Hence my questions here so I can be educated on what's right or not. So I keep looking.

My concern with 1" foam would be getting 1" of foam. With 2" I'll probably get some low spots at 1", which I think is the minimum we'd want to get in the low spots.

But you have given me a lot to think about. I really appreciate your insight and discussion. Thanks!

Posted By Dana1 on 10 Sep 2012 04:54 PM

Posted By joe.ami on 08 Sep 2012 06:29 AM
Why not upgrade insulation and go ASHP?

Into kicking over hornet's nests, are we?

I have come to understand geographical disparities in heating strategies- (you have taught me well obi-wan).

In a new build little is cheaper than shrinking the load (to a point of diminishing returns).   
Folks who have done a thousand manual J loads, come to understand ventilation requirements eventually cancel greater insulation.
KY or Boonetucky, would seem to be a good fit for more insul and less heat/cool plant as they should be relatively balanced between heat/cool......MI not as much.

I'm a geoadvocate- when it's the best technology for the job. I just suggested an electric boiler to a customer the other day.
                                                

My concern with 1" foam would be getting 1" of foam. With 2" I'll probably get some low spots at 1"

I can certainly understand that concern, but on the foam jobs I have seen, the application has been remarkably accurate. You can get (or make) a probe similar to what the foam technicians use to pierce the foam and see if the thickness is correct. It would be like an ice pick with the tip properly blunted so you could feel the sheathing when it touches. If you showed up with one of those on spray day, you could do your own verification and nearly eliminate that concern.

Yes, it does seem that when you are present things are different than when not. But I work full time and don't know if I'll be able to schedule vacation to be there for everything.

I meant to ask this question here, and posted it on my insulation thread.

I can't seem to convince the insulator that works with our general to do a flash n fill because of their concern for moisture trap and mold. So instead he's going to give me a bid for full foam cavity.

I think it's the half lb foam, and other than knowing it has less R/inch than 2lb foam, i don't know much about it. Assuming that came back cheaper than the flash n fill bids I have using 2 separate subs, is a full 2x6 cavity of half pound foam a good option with my stackup (1" iso, OSB on the exterior)?

Thanks.

you should shop your foam installer the same as your geo installer. I have seen many bad insulation jobs as people simply shopped by lowest bidder.

I can't seem to convince the insulator that works with our general to do a flash n fill because of their concern for moisture trap and mold.

Sounds like they aren't too facile with their knowledge of what is appropriate for open cell (half lb) and closed cell (2 lb) foam.

don't know if I'll be able to schedule vacation to be there for everything.

That seems like an argument for the flash coat of foam. That seems like a better path to air sealing than to have to make sure it is done yourself.

Joe - I've been talking to insulators since March. Not many do multiple kinds of insulation. They either do foam, or bib, or cellulose. I don't know how many phone calls it took me to find 1 dense pack cellulose contractor. 1!
The very few that do more than one, will not even consider doing the flash and fill. When someone did call back or replied to inquiry, after I asked what I wanted I would never hear back from them. So after two calls and messages I give up and keep looking. You have no idea how frustrated I am feeling like I'm up a creek! I'm just about ready to give up. I've been to some friend's houses that are under construction and I can tell you their insulation jobs sucked. I went to visit a couple before drywall went up. On one they used a clear plastic and the BIB looked like ice scream scoop balls of fiberglass were loose blown in, and to me that did not look like a dense packed. I could see gaps everywhere. I hoped the plastic was not meant to be some sort of vapor barrier it was so full of holes and rips. The other house the job looked much better, a bit neater job. But that contractor is not comfortable with a hybrid like I asked.

ICF - yes. It has been hard to find someone that understands what I am asking for. It has been that way since we started 4 years ago. ICF, OVE, hydronic radiant, heat loads, you name it. I have to keep searching to find the 1% of contractors that have the right kind of knowledge. And I've paid the premium for some things just because they are a niche, not the norm!

So I'm not really going for the cheapest bid. But before I had the luxury of getting the bid for the job I wanted, saving the money to get it, then buying it. But now with a loan and budget and time constraints, I don't any more. I want someone knowledgeable of what they are doing, but most seem stuck in the "this is the way we do this here" and don't want to consider alternatives. Which I understand. I don't want to tell them how to do their job. I'm trying to find someone that knows what I'm talking about and I can feel confident will do a good job.

Thanks for the discussion.

I should have added to my question about a 2x6 wall full of half pound foam: Would it give me the same or better Rvalue and performance compared to the flash n' fill for my stack-up with the 1" of iso on the exterior? No moisture/mold problems with this scenario? I know I've read that half pound foam will absorb water, like in a leaky roof. So just wondering.

Because if it is the same R value and it would perform just as good as the flash n' fill, then if it is cheaper, I could probably make enough cuts in other places to get it.

Posted By Boontucky-girl on 13 Sep 2012 03:50 PM
I should have added to my question about a 2x6 wall full of half pound foam: Would it give me the same or better Rvalue and performance compared to the flash n' fill for my stack-up with the 1" of iso on the exterior? No moisture/mold problems with this scenario? I know I've read that half pound foam will absorb water, like in a leaky roof. So just wondering.

Because if it is the same R value and it would perform just as good as the flash n' fill, then if it is cheaper, I could probably make enough cuts in other places to get it.

It's pretty close to the same whole-wall R as the flash'n'fill. Assuming R6/inch closed cell foam, R4/inch fiberglass and generic R3.5/inch open cell foam it's not a big hit at all.

At a 25% framing fraction and R6 R-board you're looking at

With bottom of the line R3.2/inch foam you get  R18.2 for a whole wall R.

with R3.5/inch generic oc foam you get  R18.9 for a whole wall R.

or about R19.9 for a 1" flash cc foam + 4.5" dense-pack

or about R20.3 for a 2" cc foam + 3.5" dense-pack

With R3.8/inch foam (Demilec Sealection 500) or R3.7/inch foam (Icynene LD-C-50) the difference between that and a flash'n'fill is less than R1, either one comes in between R19 & R20.

How much would you pay for R1?

Any o.c. foam would require either a vapor retardent paint or a semi-permeable film like MemBrain to bring the vapor retardency on the wintertime interior permeance to about 1 or a bit less to fully protect the sheathing from vapor diffusion loading, but the o.c. foam will end up about as air-tight as a flash'n'fill.

Thanks Dana1. I greatly appreciate your technical expertise. And you do a great job of keeping it simple enough that us simple folks can learn.

I'd be willing to pay for the R1 difference if the quality of the contractor warrants it. But it's a balancing act on how much I can afford vs. the quality I want to get. It seems that with the open cell I can control the paint job, since it will most likely be DIY to save that cost and we can paint. I would have to really trust the vapor barrier install. I wonder if the contractor will tell me I don't need vapor barrier with a full cavity of open cell foam? Any bets? :)

That's what my insulation installer told me, but the building official would not sign off on insulation until a vapor barrier was put up. I have 2 x 6 filled cavity open cell.

ChrisJ

Find a bucket o' paint labeled "VAPOR BARRIER LATEX", or similar, and have it (and it's specs) on-site for the inspector.

eg: http://www.gliddenprofessional.com/gliddenProProducts?other=x&platform=Special_Surface_-_Special_Task&pnameNoTrade=Vapor_Barrier_Primer_Sealer

http://duspec.com/DuSpec2/document/DocumentDisplayController.htm?documentId=934445 (<<0.6 perms at the specified coverage, which is about PERFECT)

or the Ben.Moore version at 0.5 perms:

www.benjaminmoore.com/DownloadBinaryServletTDS?fileName=20120314+260+TDS+US+OKF.pdf&propertyName=multidatasheet%5B0%5D.data_sheet_file_en_US&np=productcatalog_datasheets%2Ftds%2FTDS_0260

If they make you put up some sheet goods, do whatever you can to avoid poly sheeting. MemBrain is good though:

http://www.certainteed.com/products/insulation/mold-prevention/317391

http://www.certainteed.com/resources/3028080.pdf

MemBrain releases water fast if the humidity in the cavity-foam rises, but with dry winter air it's under 1 perm.

With o.c. foam and only R6 sheathing you DO need some interior vapor retarder better than standard latex to be safe during the 25 year extremes, but keep it at a minimalist class-II (<1.0 perms), not class-I (<0.1 perms, like poly).

If the inspector would accept kraft facers on batt insulation, if they know anything at all about the building science of it they should be THRILLED with o.c. foam + v.b. paint or MemBrain.

I'm not in the city limits. The only inspection we got was septic tank, set backs from property line, and electrical. After that... no one's coming to check... except me.

I'll see what they use for barrier, but now I know that if they say none needed, then I need to get some paint if we go open cell route. Still waiting on numbers and answers.