Using aluminum foil to reduce air-conditioning needs


July 13, 1991|By James Dulley

Q: Will stapling inexpensive aluminum foil under the roof rafters really reduce the heat inside my house?

A: Installing a radiant barrier (foil) in your attic can dramatically lower your air conditioning bills and improve your comfort. You can easily install it yourself in a few hours with common hand tools.

Even if you air-condition seldom or not at all, a radiant barrier can greatly improve your comfort level, especially in second-floor bedrooms.

A radiant barrier is a material that blocks radiant heat energy. This is the kind of heat created when the sun shines on your roof. When it does, the roof can reach temperatures of 150 degrees or more. Without a radiant barrier foil, the heat radiates down to the attic insulation and through to your ceiling.

Aluminum foil has the radiant barrier properties of high reflectivity and low emissivity. That means the foil reflects much of the roof's heat back upward. The low emissivity property of the foil reduces the amount of heat that the foil radiates on through to the attic insulation below.

There are special inexpensive aluminum foil materials available for attic radiant barriers. Although almost any heavy-duty foil zTC would be effective, foils reinforced with fibers or paper are more durable. They are also much easier to handle and staple in position.

The best location for a foil radiant barrier is attached to the bottom edge of the roof rafters. This provides the necessary air gap above and below it for best energy efficiency.

You can usually purchase the radiant barrier foil in 4- or 5-foot-wide rolls. You just staple it up under the rafters. The neatness of the job is not as critical as with installing insulation. You can install it very quickly without sacrificing efficiency.

For the greatest reduction in the heat from your roof, make sure you also have adequate attic ventilation. A combination of ridge and soffit vents is best. This creates air flow between the foil and the underside of the roof. The heat blocked and trapped by the foil is carried up and out the ridge vents at the roof peak.

You can write to me for Utility Bills Update No. 249, showing a list of addresses and telephone numbers of 15 manufacturers of radiant barrier foils, a small sample piece and do-it-yourself instructions and diagrams for installing foil. Please include $1 and a self-addressed, stamped business-size envelope.

Q: The slots in the return air register grills [in the letter-writer's home] appear to be directional. They would direct air blowing out of them downward. Is that the correct direction for air-conditioning or should I reverse them?

A: There really is no correct orientation for the direction of the slots in a return air register. Since the register draws air in, the direction of the slots make very little difference in the air-flow patterns. If the air were blowing out of them, then the direction would make a difference.

You should position the orientation of grill slots to get the best appearance. This usually means turning them so you don't see through the slots into the duct.

Questions should be addressed to James Dulley, c/o Baltimore Sun, 6906 Royalgreen Drive, Cincinnati, Ohio 45244.

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