We are in the final stages of design for our new home. Total square footage ~1700 with full basement under 1000 square feet and crawl space under remaining. Trying to plan for energy efficiency. Double 2x4 walls with cellulose insulation, efficient double glazed windows. Some insulation under foundation. Manual J was completed with Total Heating required including ventilation air: 25,116 BTUh. Efficient wood stoves planned for supplemental heat. Quotes for heating systems seem so high! We are looking at hydronic radiant floor heat. Quotes for propane boiler or electric boiler with radiant floor heat are in the $20,000 ball park. Ground source geothermal at near $30,000. So, this seems crazy to me. A small well-insulated house--should not require a $20-30,000 heating system plus wood stove costs. Where are we going wrong? Should we be giving up radiant floor heat? Should we be putting an additional $10-15,000 in insulation and reducing heating system to perhaps mini-split ductless? Direct vent propane units? Thanks for help/advice. We are in Zone 5 northern michigan. Heating is the primary concern vs. cooling.

We design radiant floor and ceiling systems for homes like yours using condensing tank type water heaters and sub-systems for combi space and domestic hot water heating. The cost can come down by thousands if properly designed.

On all homes we insulate and condensate for efficiency and comfort.

Just curious, why did you decide on a a basement and crawlspace vs a frost protected shallow foundation + slab? You might get the price down some if they dug a loop while they are out there digging the basement. IMO, geo systems should be comparable to a normal AC system plus the loop costs - so either shop around more or do more of it your self.

2 ASHP's + fireplace or radiant/DHW for deadly cold nights would be a hell of a lot less than geo I would imagine. Can you get your heat load down anymore?

On a double-studwall cellulose wall (how thick?) I wouldn't trust Manual-J to give the right number for sizing the heating system. You'd want do do a better simulation/model than that (Retscreen, DOE-2, etc).

Unless you have a large glazing fraction or left a lot of thermal bridging in place on the framing timbers odds are you're already well below 25KBTU/hr, and could heat the place ala boardom's recommendation, with a single 2-ton mini/multi-split with propane HW heater + hydronic radiation to cover for when the temps are below -5F and the mini-splits are crapping out. Panel radiators are lot less money than radiant, and even 15 cent electricity even at a seasonal COP of 1.5-2 on the mini-split (it'll likely average better than that, ~2.3-2.6) is still quite a bit cheaper than 90% efficiency condensing propane @ $2.50/gallon. As long as you locate the interior units of the minisplit so they don't blow directly on humans, bumping up the temp a few degrees for comfort is sell a heluva lot cheaper than a propane-fired radiant floor.

Even using your probably- oversized Manual J as a starting point, a 30 KBTU Mitsubishi (and probably the Daikin's too) mini/multi-split would be still good for ~22KBTU/hr at -10F for under/around ~$8-10K, depending on how many interior heads you need. That's below the 97.5th percentile heating design temp for any city in MI. (Marquette & Sault Ste. Marie are the coolest cities in my references, at -8F for a 97.5th percentile design temp. In a high-R house there's no point to using the 99th percentile numbers. )

Zone 5 is really southern MI, are you sure you're not really in Zone-6? (got a zip code?)

What are your foundation & attic Rs, and how thick is the cellulose in the wall? How many square feet of glass are we looking at? (Reducing glazed area might be the quickest & easiest tweak.)

Hi Molly.

Have you considered DIY at all? 

The HVAC pros definetly have a large markup, one of the highest in the construction business.

If you do consider DIY, you basically need to invest time to learn the basics and spend some $$ on tools if you do not have them already.  10% to 20% the cost of pro installations is typical for a diy install of the same quality - assuming you do spend the itme to learn.  If your day job pays over $100/hr the time spent learning for a one time DIY may not be worth it.  If physically disabled (is 'challenged' the correct PC?) then you may not have the diy option.

The best link I found for details on a guy that did and documanted his own GSHP for pennies on the dollar can be found at:

http://ecorenovator.org/forum/geothermal/484-homemade-heat-pump-manifesto.html


Good luck:

Stop if you have not started building!

Upgrade the insulation, Windows, sealing, and ventilation design. This can be done for 5 to 6 dollars per square foot and can reduce total heating and cooling needs by more than 70% for the life of the building. Now you do not need the expensive heating system. This is always a better investment and approach. Note that the size of the heating system can be reduced by that 70%. Planned right you can save the incremental costs of the envelope upgrades in reduced HVAC systems costs. I was on an internet TV show talking about this if you are interested.

http://www.youtube.com/user/zehboss?feature=mhee#p/a/f/0/rT78iopvtD4
http://www.zehtalk.com/

Brian

Posted By zehboss on 04 Aug 2011 03:09 AM

Stop if you have not started building!

Upgrade the insulation, Windows, sealing, and ventilation design. This can be done for 5 to 6 dollars per square foot and can reduce total heating and cooling needs by more than 70% for the life of the building. Now you do not need the expensive heating system. This is always a better investment and approach. Note that the size of the heating system can be reduced by that 70%. Planned right you can save the incremental costs of the envelope upgrades in reduced HVAC systems costs. I was on an internet TV show talking about this if you are interested.

http://www.youtube.com/user/zehboss?feature=mhee#p/a/f/0/rT78iopvtD4
http://www.zehtalk.com/

Brian

That's a pretty bizarre statement, given you don't even know how thick the insulation in the double-studwall already is.  But something like a foot of cellulose is pretty air-retardent even without better defined air-barrier, and has a significant R value.  Treating the remaining thermal bridging may be useful, but it's not going to be anything like a 50% reduction in heating load, most of which is probably from windows in a double-studwall building. (Priced sub-U0.20 windows lately?)

Manual-J is a terrible way to simulate such a building- I'd use something better.  But even at $5/foot of additional insulation & air-sealing cost, it may not make as much economic sense as just heating with a cheap mini-split rather than the GSHP & radiant floor being quoted.  Even if the Manual-J were dead-nuts on (which is surely isn't), a $5K mini-split could keep the place plenty cozy at roughly GSHP efficiencies (in most US climates.)  The real load is likely way lower than 20KBTU/hr and further reducing by half or more would take well over [(1000 basement+ 1700upper floor) x $5=] $13.5KUSD, per your estimate. 

For heat loads that low GSHP and radiant floors have no economic rationale, and only a modest rationale on comfort due to the warmer floors, but with clear-wall Rs north of R30 the cushy-toes argument isn't very compelling either, since the floors need only be barely above room temp to support the average heat load. 

I'm a big fan of putting the real money into the building envelope efficiency rather than the mechanicals, not such a big fan of exaggerated claims.  Peeling 50-70% of the load off code-min construction may be doable on the cheap, but taking 50-70% off a double-studwall high-R house?  Seriously?   (As seen on internet-TV!)

Points of facts.

Cellulose becomes an effective air barrier at 24 inches in thickness according to the manufacture's specification. 30 inches provides some safety factor to guarantee real world performance. By rating this is R 111, and an effective convective stop. The cost of cellulose is around $.75 per cubic foot. This cost very little to add to the attic. The trusses need to be designed with a thermal break to stop conduction and they need to accommodate the 30 inch heel space. Most houses loose a large amount of their energy through the ceiling. This along with proper install details will eliminate almost all of the thermal loss through the roof.

Walls: 12 inches of cellulose in the wall will not adequately air seal the walls. Expanding to 24 inches is not hard or expensive to do. The inside stud wall should be the structural system to the home. All efforts to isolate external wall conductive path should be done.

Sealing: All seams in the entire building should be spray caulked in each layer. If high humidity is an issue a non-permeable layer should be used such as 2 inches of sprayed urethane. This often should be accompanied by an air gap behind the siding, and other details.

Windows and doors: At this point the windows will be the biggest loss of energy in the house. Upgrading to triple pane windows or better will reduce the loss by at least halve as well as the benefit of lower noise transmission.

Isolation of the air intake for the dryer should be done. This large squirrel cage fan can move a large amount of your precious conditioned air out of the building.

Ventilation: All ventilation should be controlled and monitored with an ERV or HRV with merv 13 plus filtration.

Now the house can be heated with a hair dryer sized system or a few well-placed windows and you do not need the $20,000 GSHP system. All of the above will cost less than the GSHP system but will make the house passive, quiet, dust and allergen free, more comfortable, simply better for less cost. It will also run for ever without having to service the compressor etc.

Brian

"The HVAC pros definetly have a large markup, one of the highest in the construction business."

Utter nonsense. This statement should shade all following statements.

Geo is seldom cost efficient when insulation is adequate. I like the minisplits but still need DHW. Jon's question on slab-on-grade (in which case panel radiator would cost more than radiant floor heating).

As you can see, there just isn't enough information here to form a solid opinion for design. Most of my designs for modest or well-insulated homes use off-peak electricity with propane fireplace for backup or dual-duty water heaters.

Most of the radiant floor heating systems I consult on are over-sized and under controlled.

Most people building a new home should shop for an experienced (in more than one thing) contractor that can speak to different options, starting with the cost and availability of fuels.

Brian- cellulose is only ~75cents per cubic foot at ~1.5lb/ft open-blow densites, and you'd want at least 2x that density in the double studwalls just to limit settling. At 3.2lbs/foot density it's sufficiently air-retardent for foot thickwalls from a thermal and air-infiltration point of view, but whether that would be adequate for moisture control is climate and siding-type dependent. But it's twice the material cost you've suggested, and more than twice the labor cost of cheaper methods. Lower density wet spray is definitely out of the question for the 24" thick walls- this is dense-pack or nothing.

And since you don't know how much attic insulation is already in the design, nor the extent of other air-sealing measures taken, OR the U-values of the existing glazing the assertion that you're going to get a 70% heat load reduction out of HER design for $5-6/foot is just over-the top baseless.

Clearly with double-studwall construction this wasn't conceived as a code-min hack, and my presumption is that her U values are already below code-max, and cutting the heat loss those by 70% won't be achievable simply by going with a low to mid-cost triple-pane, and may not be achievable at ANY price. (The $erious 925 series has U values of ~U0.13, which would only be a 55% improvement over U0.30, and only a 62% improvement on U0.34- code-min for new construction in most of US Zone-5.) Since window losses are most likely dominating facotr already, you'd blow through the $6/foot budget pretty fast and still fall short.

I'm not saying that your recommendations don't make sense (it really depends on the extent of the existing design, eh?), only that your 70% reduction in heat load @ $5-6/foot additional cost just isn't very likely given that it's already started out as a high-R design. It's highly likely that ERV & air sealing are already part of the package- you simply don't know. Assuming she's starting out at 3ACH/50 and code x 1.5 R values, code minus 10% U-values, I'm still your biggest skeptic. A 70% reduction in heat load may be doable at the price she's been quoted for her radiant + GSHP, but that's at least twice the money you're talking.

But I guess we'll never know- she's been pretty stingy with the details...

My point was that you could make the house into a passive house design for less than the cost of the GSHP system she was quoted. That means you cannot justify the GSHP type system if the shell is efficient first. This is especially true if it is already part way there in the current incarnation. I agree with most of what you have said. The cellulose I mentioned was for the attic space, and I have actually gotten it cheaper when on sale. It has gone on sale some time during the building process for each of the last 5 houses I have built.

Climate and design specific data is required to answer these questions well. Depending on climate and design an additional $3 to $10 per foot has been able to move my clients' homes from code to passive eliminating the standard HVAC except for a small backup system.

Personally I like the insulated, stressed skin, rammed earth system I have come up with. It is lower cost, easy to build, better quality and bullet proof in a self-heated house. I call it the H.I.D.E.N. Systems, (Holistic Integrated Design using Engineered Natural Systems.)

Brian

window losses are most likely the dominating factor already

At some point you have to go with shutters/doors over the windows.

The point is that you can get to passive, self-heated and cooled for less than the GSHP costs, going further is of no value.

Insulated shutters for rooms that are seldom used are cheaper than high end windows, but it depends on the client.

If money is not an issue you can use a 5 pane system (2 glass, 3 polyimide heat film) with krypton gas. R-14 windows with net positive heat gain from non-south glass, but these are not practical.

Brian

zehboss, Could you give us a brand name for the five pane windows?

Southwall is the owner and licenser of the technology. You can see at this site. They license Serious and several others. There current best is a 5 pane Xenon filled, R-20 window that is more efficient than a coded wall. On their site you will find many mfg. depending on where you are the list is on their site. To get the 5 panes the coldest area companies are the best places. You can also order the raw materials and custom build. Some will also build to order.

http://www.southwall.com/southwall/Home/Products/Commercial/HeatMirrorInsulatingGlass.html

Brian

Thanks for posting the licenser of the technology.

Look out for kids with baseballs!

No ROI, but you will need an insurance rider.