How to get cold air from basement upstairs?

Q We have a two-story house, and in the summer the basement is cold. Is there a way to get this cold air into the rest of the house and minimize use of the air conditioning? We have run the furnace fan by itself, which brings some of the cold air up to the warmer upstairs floors, but there is a lot more potential. Can we cut a hole in the cold air duct so it can draw air directly from the basement? It could be sealed off in winter with a cover and tape. If so, where is the best location to do this?

A Your suggestion is an interesting approach to a familiar summertime situation, but it would pose potentially serious consequences, said state energy specialist Phil Smith. It could lower the air pressure in the basement, he said, to the point where a conventional water heater would send its exhaust into the home rather than up and out the flue.

And it could actually work against what you're hoping to accomplish. When the furnace fan comes on to push cold air through the duct, the hole you describe would pull more air from the basement than from the rooms. As the system tries to push more air into rooms that are not losing air, resistance would build. The result is you won't get the cooling comfort you seek.

Smith said that there are a couple of other approaches to consider. Adding both supply and return ducting in the basement would permit the movement of air from the basement without creating dangerous pressure imbalances. It would increase your overall energy use, however, because now your basement would be actively heated in winter. This work should only be done by a professional heating contractor who can measure the airflows at supply, return and chimney or vent.

Or you could tighten up the existing ducts to make your current system more efficient. Home duct systems vary in tightness between the supply and return sides. Typically, the supply side is tight and the return side is very leaky. That leakage means ducts operate as described above, resulting in warm second-story bedrooms.

Aggressively seal all the seams, joints and penetrations in the return ducting. Use metallic duct tape (not the cloth-backed duct tape) or an approved mastic that is "painted" on seams and joints. In either case, look for a product with a UL listing as a duct sealant.

If your basement is finished and you have no access to the ducting, you can hire a contractor to seal all of the ducting from the furnace area. Researchers at Lawrence Berkeley Laboratory, a U.S. Department of Energy Lab, developed a technology to do just that and it is available to you under the brand name Aeroseal. (See: www.aeroseal.com).

Continuous operation of the furnace fan as a solution to your problem can be expensive. The typical furnace fan in most homes uses a good deal of electricity. Newer furnaces with variable-speed fan motors can save up to 80 percent and may be the best option for continual fan option. If your fan isn't one of these, then run it intermittently.

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