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Old 02-04-2008, 03:27 AM   #1
Tofuball
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Insulating for A/C

I know when you insulate for heat, you want to start from the top of the house and go down, and ways to do that include properly insulating the attic, caulking and sealing around recessed lights, vents, etc, and working down from there.

My question is, is insulating for A/C simply the reverse?
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Old 02-04-2008, 07:39 AM   #2
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Be sure your attic is well vented in summer. Otherwise it gets up to 150 degrees or so and your drywall ceilings will act like radiant heaters. Some folks have the self spinning stack type vents in their roofs and then cover them up for the winter, others have thermostatically activated electric fans through the roof or at the gable ends. Make sure there are vents under your eaves also so cool air can enter the attic.

Watch out for the sun's rays also- close the east window shades in the morning and close the west shades in the afternoon.
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Old 02-04-2008, 07:46 AM   #3
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Quote:
Originally Posted by Tofuball View Post
My question is, is insulating for A/C simply the reverse?
Not necessarily. You're concerned with heat getting in instead of heat getting out, but one of the main sources of heat intake is the roof, just as it is of heat loss in the winter.

One main difference is that AC would greatly benefit from cool roofing materials, whereas regular asphalt shingles are fine for keeping the house warm. Cool roofing materials are a bit more expensive, but they may pay off in the long run depending on the local climate. Of course, that's mainly an option if you're putting on a new roof anyway.

Insulating your boiler and hot water lines should help with the AC as well.
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Old 02-05-2008, 01:42 AM   #4
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Originally Posted by Erik View Post
Be sure your attic is well vented in summer. Otherwise it gets up to 150 degrees or so and your drywall ceilings will act like radiant heaters. Some folks have the self spinning stack type vents in their roofs and then cover them up for the winter, others have thermostatically activated electric fans through the roof or at the gable ends. Make sure there are vents under your eaves also so cool air can enter the attic.

Watch out for the sun's rays also- close the east window shades in the morning and close the west shades in the afternoon.
Hrm, OK, My roof has no vents at all, and no sophets. So I'll plan to install a thermostatic roof fan in the spring. Thanks for the advice

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Not necessarily. You're concerned with heat getting in instead of heat getting out, but one of the main sources of heat intake is the roof, just as it is of heat loss in the winter.

One main difference is that AC would greatly benefit from cool roofing materials, whereas regular asphalt shingles are fine for keeping the house warm. Cool roofing materials are a bit more expensive, but they may pay off in the long run depending on the local climate. Of course, that's mainly an option if you're putting on a new roof anyway.

Insulating your boiler and hot water lines should help with the AC as well.
Thanks for the advice, I googled "cool roofing materials" and found a lot of great stuff!
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Old 02-05-2008, 03:19 AM   #5
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If you put in a roof fan for cooling purposes, you will also want to put in some kind of vents to allow air to flow into the attic space, so you have good circulation.

Light colored roof shingles make a big difference, too. Black roofs should be illegal on an energy saving basis.
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Old 02-05-2008, 08:33 AM   #6
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You can buy solar powered fan roof vents as well, they do cost a bit more but are self contaned so they will save you the cost of wiring, and save you on your electric bill.
The ground is pretty close to 55F all year round once you get below the frost line, the main reason for insulating the foundation of a house is to keep the cold from the frozen ground out, so in the summer nearly all that heat is coming from above, like was said, white, silver, grey, or any other light/reflective color will help keep your house cool in the summer, and in the winter those light colors will help keep the snow on your roof, and that snow will act, to a point, as insulation, keeping your roof 30F insted of the -10 that it might be outside.
while you are adding insulation to your atic, make sure that you don't block off any vents to the outside that might be in your eves, you can buy chanals that keep that space from filling with insulation so that you keep air in that unheated space moving, and most roof vents are labled with how many cubic feet of space they can vent so do your best to make sure you have enough.
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Old 02-06-2008, 02:56 PM   #7
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While you are in the attic, think about installing a radiant barrier. You can find rolls for sale on the web if you google it.
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Old 02-14-2008, 07:29 PM   #8
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I read an interesting article in a Fine Homebuilding publication this week that talks about the inefficiencies of A/C and heat pump systems in general as a result of improper installation and sizing. What really caught my attention in the article however was the fact that the majority of systems are installed with an incorrect level of refrigerant, causing a 20% or greater impact on efficiency from the moment they are turned on.

They also mention that the greatest energy load for most homes in the summer is a result of A/C use, comprising a majority of kWh used. So put another way, anybody faced with $200 electricity bills during the summer in a warmer climate could potentially save at a minimum, $20/month just by assuring that their system is operating with the proper amount of refrigerant. (Likely more.)
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Old 02-14-2008, 07:44 PM   #9
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I just did a major renovation, and while the walls were open I decided to go big and did spray foam.



It's very expensive, but the benefits are that its totally airtight and waterproof. Very efficient. I don't have actual numbers, since I haven't moved in yet (soon I hope). And then, I can't A-B-A it :/

One thing that I've heard about AC systems is that you should run your ductwork in the conditioned space. Less heat gain from hot attics and if there's a leak, it'll just blow cold air into the room.
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Old 02-14-2008, 08:05 PM   #10
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Yup, the ductwork and air handler should ideally be in the conditioned space for best efficiency. Another article in the same magazine suggests that it is far better to have conditioned crawl spaces than unconditioned vented ones, both from an efficiency standpoint, and from the standpoint of keeping moisture accumulation low. As for attics, piling it deep never hurts and is easy to do with loose fill.

In fact, after reading through that issue, I have firmly decided that whomever installed our HVAC system didn't really have or clue or didn't care enough to bother with doing things right. So tommorrow we are having it serviced, admittedly for the first time since we moved in here 5 years ago. (And we suspect is hasn't been touched since it was installed 11 years ago aside from filter changes and when I cleaned the air handler myself and replaced a faulty motor start capacitor.)
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