gnick540
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| 09/27/2009 9:39 AM |
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| My GSHP installer strongly advised me to include a fully insulated attic (aka "conditioned")with my new Water Furnace equipment because it would reduce the summer heat load and thus allow me to retrofit smaller units (7 tons vs 9 tons). In June, he showed me an installation that was nearly complete, and I was very impressed with the reduced attic temperature on a 97 degree afternoon in Dallas.
My entire attic is now sealed and insulated with 5 inches of open cell foam. The contractor has removed all the blown fiberglass that was installed in the ceiing joists 20 years ago and says it's no longer necessary. He told me that is the way they are doing it on all new construction. I am not convinced this is a good idea because there will always be a delta T between the living space and the attic, so heat will always be migrating from the warm side to the cold side.
Has anyone else faced this issue? I would like to hear arguments for either side. |
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rykertest
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| 09/27/2009 2:11 PM |
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| He could of left it without any issues, but taking it isn't a big deal either. My opinion on this is that you will be better off with a conditioned space (which I assume you agree on) and the temp. variance won't affect the home THAT much. Each situation is different of course. Is the unit suspended in the attic or sitting on the joists? All in all it's not something I'd worry about. If it is, bring it up to him and share your concerns. If there is an issue will he come and fix the situation? |
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engineer
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| 09/27/2009 3:40 PM |
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I prefer closed cell foam for attics, since closed cell adds strength and a vapor barrier, but either is a great improvement over the conventional method.
In his place I would have left the fiberglass in place a I coan't think of a good reason to take the trouble and expense of removing it. |
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Without data, you only have an opinion. |
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joe.ami
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| 09/27/2009 9:25 PM |
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Age old argument: condition the space or compensate for it....
both have merits. In northern climates unconditioned basements have similar load additions to the ground floor as conditioned basement loads. While i haven't looked I would suppose attics would be similar in cooling dominated climates.
I agree with Curt that actually removing insulation has no imaginable benefit.
More importantly how did the contractors references check out?
Good luck,
joe |
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Just a Mechanic;
Geothermal; Savings Underfoot |
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gnick540
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| 09/27/2009 10:21 PM |
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| First off, the contractor is perhaps the best in Texas; he is reported to be the largest WF dealer in the state. GSHP is his only business. He's been doing it for twenty years and does not advertise or own a website. I trust him without reservation for all things related to heat pumps, but I do know a little about thermo, and he's not explained his rationale for the removal to my satisfaction.
I believe his reason for removing the insulation was to expose the joists for easier/safer mobility in the attic. The units will be suspended from rafters on all-thread with neoprene hangers.
Joe, your basement analogy is excellent. Perhaps the attic isn't any different [edit] except that subfloor and carpet provide more insulating value than does a single layer of 5/8" drywall in the ceiling. |
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joe.ami
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| 09/28/2009 4:31 AM |
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Impeccable references work for me.
I see an added benefit to the service man down the road in not having to work in a 140 degree attic.
j |
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Geothermal; Savings Underfoot |
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engineer
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| 09/28/2009 8:54 AM |
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Temperature excursions in vented attics are much more than in basements, which is a fancy way of saying they can get very very hot in summer as well as cold in winter.
Attic temps here can climb to 140 especially with dark asphalt shingles which still seem to be the norm. That's an 80+ degree gradient hitting the system cabinet and all the ductwork in the attic. During the off cycles that heat soaks into the cabinet and ductwork. Our R20 (or whatever) walls might see a 25 degree gradient on a hot day, but the R6 duct and R3 or so cabinet fights 80 degrees. When the unit starts the warm air in the heat soaked ducts is the first thing that hits the living spaces.
Guys doing installs or repairs in hot attics are extremely unlikely to produce the same quality workmanship they might otherwise. Being hot and sweaty and itchy from fiberglass insulation is a truly miserable combination not conducive to sealing every little potential duct leak. Getting rid of the fiberglass might reduce the itch and simplify installation. |
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Without data, you only have an opinion. |
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gnick540
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| 09/28/2009 11:43 PM |
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| I agree that insulating the attic was a good idea for several reasons - no debate there. My question is whether removal of the ceiling insulation between the living space and the attic is acceptable. If we assume a 10-15 degree difference on the hottest/coldest day of the year and there's no insulation between the two spaces, a LOT of heat will migrate thru the ceiling. Does anyone on this board have a conditioned attic with no ceiling insulation?
I am reconsidering the similarity between the conditioned attic space and a basement. Besides the difference in R value between a carpeted floor and a drywall ceiling, there is less tendancy for heat to migrate downward to a cold basement than there is for heat to migrate upward thru the ceiling. |
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engineer
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| 09/29/2009 5:04 AM |
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I do - 3" of closed cell sprayfoam. My delta T runs 5 or so degrees on hottest days. Stuff is definitely doing its job since I've measured 160+ deg F under shingles.
The ceiling assembly probably runs around R2 so I may pick up a couple thousand Btuh on the hottest days. If I did it again I'd have gone for 4" and insisted the spray foamers encapsulate the 2x6 top chords of the trusses. On very cold mornings when frost forms on the shingles I can tell right where the chords are beneath the shingles - frost free!
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Without data, you only have an opinion. |
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joe.ami
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| 09/29/2009 5:33 AM |
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Posted By gnick540 on 09/28/2009 11:43 PM
there is less tendancy for heat to migrate downward to a cold basement than there is for heat to migrate upward thru the ceiling.
You lost me on this one, are you worried about losing heat in the winter? If this is about cooling then aside from your carpet proviso, I would think that for cooling and heat migration the uninsulated basement is worse.
j |
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Just a Mechanic;
Geothermal; Savings Underfoot |
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