So Todd,
If you recognize that auditors don't work for free and that they are subsidized by utilities (guaranteed a profit by law) who collect from all customers for the benefit of a few, or the feds who collect from all for the benefit of a few....why would you ever suggest there is a free lunch?
Not every auditor shows up with a door blower or infrared camera or other things you picture in your minds eye. Most energy audits are a check list. Do you think the prescription changes from house to house? Do you think the blower door test has giant revelations......(Oh, you are leaking here around this window; who'd a thunk it)?
Not suggesting they never have there merits, I have employed an auditor or two, but rest assured, an auditor is in the business of selling an audit or something else (many have arrangements with weatherization or insulation companies). Few guarantee their projected energy savings.

I'm going to guess you have little experience with the government or utility expenditures or you might not be so smitten. There is a lot of waste.....one generic example is one might take advantage of tax credits or rebates to replace a 95% efficient furnace with a 95% efficient furnace. How much energy savings would you predict from that? I was asked to bid such a project and declined.

Suggesting load reductions might save you half the equipment cost is ridiculous as well. Using 2 ton instead of 4 ton equipment will never reduce your price 50%.

Nobody here suggests you ignore the low hanging fruit envelope improvements. That is no panacea either however as there are a lot of diminishing returns. Usually with caulk and insulation (far more than $500 btw- we are talking about government involvement) one can cut 10% or so off their energy consumption, a 50 % reduction in load however (if possible) might require windows, doors, siding etc. (still not a bad idea) but then you might be talking tens of thousands of dollars.

BTW while you imply I'm all about the bigger geo sale did you forget this comment I made before you ever weighed in:
"17 Jun 2011 09:15 AM Edit
ETF,
...........
if you want to enter the world of doing your own load calculation, you can check different insulation values and such with the click of a mouse. You might find that very little needs to be done to cut your load by 10% or you might find it's cheaper to close your blinds...........
Good Luck,
Joe

Just a Mechanic;
Geothermal; Savings Underfoot"

If your point is low hanging fruit load reduction, then system design- I already covered that for you.
j

For the type of insulation retrofits EricTheFred's contractor was trying to sell him on I would anticipate signficantly more than a 10% reduction in peak cooling load.

Not all air-leakage is dead-obvious. In most homes leaking at the foundation sill exceeds all the window & door leakage combined. Fix all of the most-obvious & egregious leakage and insulation deficits BEFORE committing to a blower door test if you want it to be a worthwhile exercise.

"Thick foam" isn't usually used in the same sentence as "cost effective", particularly in attic apps. Radiant barrier is only useful if the ducts & air handlers are in the attic, above the insulation. For the same money in an R20-R30 attic you'd get better bang/buck out of a cellulose overblow (particularly if the existing insulation is low-density fiberglass, batts or blown, and the joists or truss-chords are above the top layer of insulation.)

If a 2.5 ton 8.0 SEER antique is keeping up with the load, there are probably any number of mini-split & mutli-split R410A solutions for cooling the 1260' of space at less than half the cost of geo, but may be at par or slightly higher than a high efficiency ASHP retrofit for the ducted system. But if the ducts are in the attic, a higher SEER retrofit is not a guarantee that the ducted system will use less power than a lower SEER ductless mini or multi-split, and will likely underperform a ductless system at identical SEER ratings. Duct leakage and air-handler-driven air infiltration, & duct gains as well as air-handler power all need to be taken into account beyond mere SEER consideration when comparing ductless & ducted system performance.

By fixing the obvious first then paying for, a better-than-punch-list energy audit and taking a most-cost-effective approach to the rest of the air-sealing & insulation, odds are pretty good peak loads would be well under 2 tons and total heating/cooling energy use cut by a quarter or more. If the true peak load is closer to 1.5 tons, a high-SEER 3 ton ducted system may not hit it's ratings, as-installed, but there are dozens of mini-splits options that would.

A simple-minded but still useful overview of actual vs. rated performance for ducted systems, lives here:

http://www.advancedenergy.org/buildings/knowledge_library/heating_and_cooling/seer_facts_bulletin.pdf

With variable speed scroll compressors some of the performance hits of 2x oversizing isn't quite as bad as in that document, but the duct issues still count big-time. If you're not using the ducts, it won't matter if it's 120F in the attic, and if you aren't moving air to & from individual rooms the effects of wall-leakage drop, since there's no air-handler induced infiltration even if the walls are still leaky.

Posted By EricTheFred on 16 Jun 2011 02:13 AM

We had the sales people in today with a hard sell of a 3 ton 16 SEER air-source system to replace our 2.5 ton, 8 SEER antique, along with adding radiant barrier, 21 inches of sprayed insulation and a variety of required changes thanks to our old air-handler being a 'pancake unit' in a space too small for a higher SEER air handler. Even after the all the great discounts that of course were going to run out any day now, this was an $11.5K job. I got them to price a 13 SEER system that used a pancake air-handler for slightly more than half this price.

This is a little surprising to me, since the cost difference between a 16 Seer system and a 13 Seer system is less then $1,000. I know contractors pad there numbers a little, but I can't believe there is that kind of cost difference when your talking about still having to pay all the labor involved. 

Posted By TechGromit on 28 Jun 2011 12:35 PM

Posted By EricTheFred on 16 Jun 2011 02:13 AM

We had the sales people in today with a hard sell of a 3 ton 16 SEER air-source system to replace our 2.5 ton, 8 SEER antique, along with adding radiant barrier, 21 inches of sprayed insulation and a variety of required changes thanks to our old air-handler being a 'pancake unit' in a space too small for a higher SEER air handler. Even after the all the great discounts that of course were going to run out any day now, this was an $11.5K job. I got them to price a 13 SEER system that used a pancake air-handler for slightly more than half this price.

This is a little surprising to me, since the cost difference between a 16 Seer system and a 13 Seer system is less then $1,000. I know contractors pad there numbers a little, but I can't believe there is that kind of cost difference when your talking about still having to pay all the labor involved. 

Careful you don't fall into the "the condenser is only $1,000 more so the system should only be $1,000 more" assumption.
here's what you didn't consider:
First OP indicated significant duct or mechanical room changes if "pancake air handler" was not re-employed.
Second to get a 16 seer AC to deliver 16 seer one must match it with the rated air handler (as much as twice the price of a PSC air handler).
Third new thermostat wire to handle extra (multistage) signals.
Fourth multistage thermostat.
Fifth often larger lineset is required.
Sixth this came with "radiant barrier and 21" of sprayed insulation"
Finally PITA factor- everything takes longer from installation to start and charge up to tax credit or utility company rebate paperwork.

You are always even handed TG and I'm not picking on you, just offering balance to your "first blush" reaction to the price difference.
j

I've been reading your response as they get forwarded to my email, but haven't gotten around to logging back in to thank everyone again until now. So, thanks much to everyone for your advice.

joe.ami: your analysis is correct: Even though many of the items you mention were being 'thrown in for free', since the TANSTAAFL rule answers that, these are the explanation for the large increase, not just moving from 13 to 16 SEER.

Just to let everyone know, after consulting a few different people and bringing in one geo contractor to look at the situation, my wife and I came to a couple decisions that we felt made sense.

The geo contractor would not discuss a horizontal ground loop, slinky or otherwise, in North Texas at all. He feels they are not a good choice in our soil and with our heat absorption. Also wonn't do DX in blackland prairie soil. (This makes sense to me: the soil in NT is extraordinarily destructive to foundations, water and gas mains, roads, etc. Ground shift is powerful enough that my neighbor once lost electric service because the shift busted the buried supply cable.) So basically the choice was a vertical water ground loop.

The good news was, he could do it, and after doing his calcs (not one the spot; he actually mailed us the quote after several days) he quote us a step down to a 2 ton GEO system, but recommended we also install open-cell foam under our roof or the 2 ton system might not be sufficient (he would not do a 'legitimate' manual J because he had no way to confirm our wall insulation, but he was concerned from his 'informal' calculations that we were probably right on the line for whether 2 tons would do it or not.) The total quote, including foam, drilling and all, worked out to slightly less than the other guy's 16 SEER system after the tax credit.

However, he also recommended that we carefully look at our electric bills and do some calculations as to whether we would see an actual ROI, since he had his doubts this would happen on a house as small as ours until electric rates increase dramatically.

I did those calcs and came to pretty much the same conclusion. Factoring into that decision was that we had found a commercial HVAC contractor (one who does businesses and apartments) who quoted us $4200 to replace our 2 1/2 ton system with a 13 SEER at the same tonnage.

I'm still looking at the geo guy's separate quote for open cell foam. Without bundling it with the geo system it can't qualify for the 30 percent credit, but even at the full rate and including removing the old insulation so we don't get humidity problems, he got it under $4.5 K, which looks like a good price to me. We are probably going to go for this. This is a subject for a different sub-forum, of course, so when I have researched enough to feel I know what to ask, I'm going to start a thread there if I have questions.

Again, thanks much to all.

EricTheFred: "...including removing the old insulation so we don't get humidity problems..."

Who did the analysis on that? In Dallas even the OUTDOOR wintertime temps are higher than any reasonable indoor-air dew point, and in summer the space between the new & old would have to be below ~70F most of the time to get moisture accumulation from exterior moisture drives. I've seen foam-guys insist on removing fiber insulation on dubious (or no) grounds, but I've yet so hear of a situation in the warmer US climate zones where leaving it in place created an actual (or even theoretical) problem. I suspect the whole rationale is largely foam-installer mythology or lore based on anxieties about what might have might have happened to some installer who got sued in ND rather than anything actual that occured in TX. (I haven't read of any cases like that in ND either, but I might be able come up with a theoretical basis on how it might create a problem, in some instances.)

With uninsulated or low-R ducts in a TX attic you're more likely to run into summertime condensation issues with a VENTED attic than a sealed attic, independent of R values, since with dew points in the 70s even the surface of less-insulated ducts can be below 70F and susceptible to condensation. With a sealed attic and R value overhead, attic, and thus the surface of the ducts are now cooler, but the interior space runs at the same absolute humidity (dew point) as the interior conditioned air. The dew point of 75F 50% RH conditioned space air is ~55F which 15-20F cooler than the average July dew point of Dallas outdoor air which is in the low-70s. Even if the attic air is now 20-30F cooler with the foam installed, the surface of the duct insulation won't be. And if the ducts aren't in the attic, there effectively ZERO risk of creating a moisture problem.

What you end up with by removing the old insulation is lower R-values, and bigger heating/cooling loads than what you would have had if you'd left it in place. If you leave it in place and are worried about it, buy a $12 humidity & temperature monitor and check now and again, both in July and in December, and during the cooling season check for surface condensation on the ducts. Unless it's staying above 65% RH (either season, any temperature) for weeks on end your odds of getting mold growth is limited- if there's any risk at all it'll be duct condensation during peak usage, and even that risk is more likely to be REDUCED rather than increased when going to an unvented attic with an insulated roof deck.

I'm betting in the current vented attic in July it hits 65% RH pretty often overnight, but under the sun-baked heat of the day it falls driving any accumulated moisture from the wood. But in most of the humid south vented attics introduce more moisture than they purge.

You may find this a useful read:

http://www.fsec.ucf.edu/en/publications/pdf/FSEC-CR-1496-05.pdf

Sounds like an honest injun

Posted By Dana1 on 30 Jun 2011 02:23 PM
EricTheFred: "...including removing the old insulation so we don't get humidity problems..."

... In Dallas even the OUTDOOR wintertime temps are higher than any reasonable indoor-air dew point

... in summer the space between the new & old would have to be below ~70F most of the time to get moisture accumulation from exterior moisture drives.
 
... I've yet s[t]o hear of a situation in the warmer US climate zones where leaving it in place created an actual (or even theoretical) problem.
 
... With uninsulated or low-R ducts in a TX attic you're more likely to run into summertime condensation issues with a VENTED attic than a sealed attic, independent of R values, since with dew points in the 70s even the surface of less-insulated ducts can be below 70F and susceptible to condensation.
 
With a sealed attic and R value overhead, attic ... interior space runs at the same ... (dew point) as the interior conditioned air ... [which] ... is ~55F which [is] 15-20F cooler than the average July dew point of Dallas outdoor air ...

What you end up with by removing the old insulation is lower R-values, and bigger heating/cooling loads than what you would have had if you'd left it in place.
 
... Unless it [attic RH] is staying above 65% RH (either season, any temperature) for weeks on end your odds of getting mold growth is limited

I'm betting in the current vented attic in July it hits 65% RH pretty often overnight, but under the sun-baked heat of the day it falls driving any accumulated moisture from the wood.
 
You may find this a useful read:

http://www.fsec.ucf.edu/en/publications/pdf/FSEC-CR-1496-05.pdf

I've contemplated for some time sealing/foaming my now-ventilated attic on my single story 3400 sf residence.  Like others, I've been told that in doing so, I would need to have my existing blown-in loose fill attic floor insulation removed.  Dana1, your post is thus exceptionally helpful - thank you!

Some comments:

Confirming what you estimated, the avg outdoor temp in Dallas this past year, Dec., was about 53°F.  In Jan. and Feb. it was about 48°.  Indoor DP gets down to about 39° at the coldest times of the year (68°, 35%).  This data comes from http://www.welserver.com/WEL0043/ , an energy savings monitoring system I've had at my residence here in Dallas for a number of years.

If I were to foam the attic roof and seal the attic, in Summer it would be incredibly difficult to get the space between the new and old below 70°.  Interior room temps would have to be very cold, requiring a tremendous amount of cooling.

Outside DPs here in Dallas at the moment, with our current 100°+ days, are getting up to about 78° at the peak of the day, and down to about 70° at the coolest point of the mornings.  See system reference.

All of my supply and return ducts are in my hot attic, insulated with R-8.  I don't have any evidence of condensation anywhere.

Right now, during these 100°+ days, my inside DP is about 54° (78°, 43%).  This DP, which is what my attic might be at if it were foamed/sealed, is at least 16° cooler that the coolest outside DP I'm going to see for a while.

There was only one month in the past 12 where outside RH averaged greater than 65% (Sep. - a lot of rain).  But even so, that's an average, with RHs lower during the day than at night.

Outside RH over 65% at the moment does occur daily, but only for a few hours centered up on the coolest morning temperature.

I thought the document reference was particularly interesting.  I'm convinced, here in the Dallas area, if/when I procede to foam/seal my attic, I'll not bother to remove the loose-fill blown-in insulation on the attic floor, saving probably some good expense.

Thanks Dana1 for contributing your knowledge to the rest of us!

Best regards,

Bill

I think Dana's point is worth asking the insul contractor about, but I would not automatically discard any "boots on the ground" suggestions. Ask insul guy what his experience with condensation has been and see if he has a compelling reason to proceed as described.
Remember where condensation can do harm we have to be right all of the time not most of the time.
j

Unless it's so much condensation that it is actively dripping and pooling, being right only 99% of the time is OK. Wood & paper can buffer quite a bit of moisture without damage as long as it doesn't stagnate for weeks/months at moisture levels that support mold or rot. I'm sure you get copious condensation on your bathroom walls every time somebody showers, but the wall doesn't fall apart or rot internally as long as it's dry most of the time.

In the Dallas area attic case the risk of condensation on the ducts are higher with a vented attic, since there's a constantly replenished source of moist exterior air to come in contact with the cool ducts. If unvented the duct is now in contact only with drier, air conditioned, indoor air. In winter the insulated roof deck keeps any wood/paper in the intervening space well above the dew point of the more humid interior air.

A high outdoor RH is meaningless without knowing the temperature that it's relative to. The outdoor dew point during those rainy Septembers is the relevant data. If it's steamy-rainy and warm the AC would presumably be on, drying out the interior air (and the attic air along with it). If it's a cool-rainy the outdoor dew point is already below anything that would cause a problem indoors.

Take a peek at this- select monthly data, and select both temperature and dew-point graphs:

http://weatherspark.com/#!dashboard;a=USA/TX/Dallas

Any time the outdoor dew points are above 60F there's a real sensible-load for the AC to be chewing on, and the semi-conditioned attic space between the roof deck insulation and floor insulation would be warmer (lower RH) than the conditioned space air- no condensing going on there. Mid winter dew points average in the low-mid 30s, cooler than the outdoor air, and much cooler than the semi-conditioned air between the roof/floor insulation, no condensation going on there either.

Dana your advice is often spot on, but you need to see this issue from another perspective.

When you are responsible for the work and the results you are more cautious.
In this case you could be right and the local contractor who owns the outcome may not want to settle for right "only 99% of the time".
Imagine this in court........
So installer bob you ignored industry standards and local practices and now newb has mildew in the attic. Why do you suggest you are not responsible for an expensive abatement? Because Dana said it's ok? Dana who? Is Dana going to pay for the abatement?
Now imagine the same conversation with the liability insurance company, just before they drop bob.

The only absolute to a contractor is; who gets the bill if I they cause damage even if it's only a freak weather occurence (that 1%). So they darn sure need to make sure their practices are defensible.

j

A 1% condition happens every year, often multiple times. The freak weather occurence that it would take to create sufficient moisture accumulation for a (temporary) mildew condition in this case would a month or more of absolute record breaking cold, something like a 0.0001% condition.

As the homeowner I'd happily sign the waiver and monitor the humidity in the attic. YMMV.

I don't blame insulation contractors for not doing the case-by-case building science on moisture potential, but in the absence of any credible evidence of moisture problems being created by leaving the floor insulation in place, and no supporting theoretical basis as to how that might occur I view it as extremely low risk. (Again, YMMV.)

The marketing folks at spray foam companies are really fond of the "...(x) inches is all you need...", that also goes along with the notion that all competing products are useless crap an should be disposed of ASAP. Where the notion that leaving the old goods in place creates a problem came from is still mysterious to me.

Can ANYBODY point me to online evidence of where sealing an attic with foam insulation on the roof deck and leaving floor insulation in place created a moisture problem in the attic? (Any climate, any R values.) If it exists I'd very much like to see it and try to analyze it.

Removing fiberglass in an attic that may have had mold conditions at various times in it's history (such as from condensation dripping from ducts exposed to humid exterior air) can itself create an indoor air quality problem by distributing the mold spores. If the stuff it really REALLY filthy there may be valid reasons beyond moisture accumulation to get rid of it though. (Decades long accumulation of mouse-nests & bat-poop, etc.)

FWIW: I ran this issue by experienced green building resident experts on a different web-forum, two experienced builders/retrofitters (one of whom currently runs a construction business in humid-sticky GA) agreed that leaving the attic floor insulation in place has no negative consequences, only positives (unless the mouse-nests and bat-poop were overwhelming). Another benefit mentioned there I hadn't considered is that with the attic floor insulation removed room-to-room sound transmission goes up. Leaving it in place enhances privacy, not just thermal performance.

In a case where there was insuffient R at the roof deck to prevent wintertime moisture issues in the now-unvented attic (say, 2" of closed cell foam on a roof deck over R50 fiberglass in Whitehorse Yukon) the solution isn't to reduce or remove the insulation at the floor, but rather to add more air-impermeable foam at the roof deck.

It's easy for me to envision a roof leaking into a sealed attic and the sealed attic rotting and molding before anyone notices. The neighbor with the same leakage doesn't have a problem - because his attic (aka rain screen) is vented in the "standard practice" way. If you open the attic to the inside or the outside, then you get ventilation and more drying - but that means you can't split the insulation.

Unconventional design ideas are absolutely worth discussing, but the "sign off on it and be liable" issue is huge. If one customer out of a hundred sues, you are probably out of business.

Posted By Dana1 on 07 Jul 2011 04:21 PM

Take a peek at this- select monthly data, and select both temperature and dew-point graphs:

http://weatherspark.com/#!dashboard;a=USA/TX/Dallas

Any time the outdoor dew points are above 60F there's a real sensible-load for the AC to be chewing on, and the semi-conditioned attic space between the roof deck insulation and floor insulation would be warmer (lower RH) than the conditioned space air- no condensing going on there. Mid winter dew points average in the low-mid 30s, cooler than the outdoor air, and much cooler than the semi-conditioned air between the roof/floor insulation, no condensation going on there either.

Dana1, thanks for the weather data reference.  Very nice presentation of the data.

I think your last paragraph, quoted above, is a key comment.  Where I live, outside DPs consistently go above 60° in the April time frame, and continue consistently above 60° through about Oct.  This matches the time period I have to use some amount of cooling A/C.  Thus, indeed the attic space would be slightly warmer.  And with the A/C unit(s) working away keeping indoor RH around 45%, I can't see how any condensation can occur anywhere in the attic.

My data shows that mid-winter inside DP ranges from 30 - 35°, just as you note.  And the data shows that outside regularly get upward of 40 - 45° DP during the day.  So yes, I can see, for my location, I would not have to be concerned about winter attic condensation either.

Thanks for the illustration.

Best regards,

Bill

I've been away awhile - starting a new biz is incredibly time consuming.

I'm with Dana on all this. We've had the "existing ceiling insulation discussion" amongst ourselves and our favorite foam guy and all agree it is best left in place. I'm utterly unable to conceive a situation where existing insulation contributes to mold in the attic.

We have had one hard lesson from sprayfoam retrofits - in no case has retrofitted sprayfoam come remotely close to actually airsealing the attic without removing the soffits and foaming the eaves from outside the house. We suspected this from higher than expected dry and wet bulb temps in attics post foam. We easily confirmed it using a blower door - thousands of CFM of swampy Florida air filling the attic and home via attic access within seconds of firing up the blower door.

That said, returning to the OPs original issues - while keeping in mind the fact that internet advice is free and typically worth every penny, I'd bet that a house that cooled adequately with 2.5 tons with air handler and ductwork in a vented attic would see a Man J load of 1-1.5 tons post sprayfoam if attic airsealing was confirmed by test.

In that scenario, the equipment of choice for me would be a Trane 20i 2 ton system since in low stage it drops to 1 ton, the only system I know that drops to 50% (rather than 70%) capacity in low stage.

Two jobs ago I dropped a house (3800 SF, 2002 code minimum construction) with 7 tons of capacity to 5 post foam. My error was not sticking to my guns and insisting on 4 tons. Nevertheless, everyone is quite pleased with the results

The next one back we went from 5T to 3T on 2900 SF. Homeowner said 5T didn't keep up on days >95*F, 3T now does.

Next up is a 3100SF house with 7T. My man J package insists that 3T will do, post foam.

Good tip on foaming the soffits from the interior to achieve a better air seal, they can be nearly impossible to get to from the interior, particularly on lower pitched roofs.

Post back how you make out on that 7 tons==> 3 tons project. (It's often hard to sell a 50%+ reduction to the client, even with some conservative math to back it up.)

Foam guy went from a non-believer to convert one hot day I pressurized a client's house while foam crew was there on callback. It was a 95 degree day. One of his crew was on a scaffold near the soffits in a corner and announced he wasn't moving from that spot for the rest of the day...

Why??? because standing there felt like being right under an AC supply grill - cold air from the house was blowing down on him that strongly. When they opened the soffits they found holes a cat could walk through despite having been certain of a tight foam job.

That sounds like the right kind of test for ANY retrofit conversion to unvented attic!

Eric,
Very interested in your quotes and the price of geo thermal in Dallas! What were the prices of the quotes for the geo + drilling install? Thank you for your help!

Chris