Hot Air On The Rise Calls For Air Management

HOME WORK

June 15, 1991|By Karol V. Menzie and Randy Johnson

It's 98 degrees and you don't have air conditioning. Summer has begun. Are you doomed to swelter?

Not necessarily.

There are a lot of reasons why owners of older houses haven't succumbed to the lure of central air conditioning. Central air systems require one set of ductwork to deliver cold air and another set to capture hot air for recooling. Even if you already have forced-air heat, you may still need an air return system. For the most efficient cooling, you need air returns at the highest possible point on every floor. You may even need returns in every room.

If your house doesn't need a major rehab, or has already been re- stored to historical standards, you may not want to tamper with the interior by installing the ductwork required.

If you're very fussy about the historic look of your house, you probably don't want window air conditioners hanging off the street side of the property.

And finally, if you're contemplating a major rehab, or just have finished one, air conditioners of any kind just may not be in the budget.

What's the alternative? Air-handling. It's simply a matter of managing the air flow and heat buildup from the sun to reduce the interior temperature of the house.

One of the basic principles of heating or cooling is that hot air rises to the highest part of the house. If the hot air is exhausted out of the top of the house, the cooler air will be drawn in at the lower levels. As long as the air coming into the house is relatively cool, the temperature inside will be lower.

There are active and passive ways to manage air. Our ancestors were keenly aware of air-handling, and if you live in an older house, it may already have some of the most effective passive features: ventilating skylights over a stairwell or in a bath; transoms that open; a central air shaft with windows and TC ventilating skylight; deep eaves or porches with roofs that keep direct sunlight from reaching the windows; interior partition walls that allow hotter spaces to be closed off; interior or exterior clerestory windows; windows on opposite sides of the structure to facilitate breezes; shutters; an air space under the house (especially in the south); and trees in the right places.

"The best thing you can do is have a big tree on the south side of the house," says Gustin Kiffney, of Energyworks, a Baltimore-based energy consulting firm.

You want to stop the sunlight before it reaches the house, Mr. Kiffney says. Block it on the south and west sides, keep it from hitting the windows. "Once the sun hits the glass, you start getting a greenhouse effect," he says.

If you don't have big trees or structural sun blocks, you can use awnings, though if you live in a historic district there may be restrictions on where they can go. Awnings will be more effective on the south side, where the sun is higher. On the west side, the sun hits the house at a much lower angle and awnings are less effective, though Mr. Kiffney thinks they may still be worth installing.

Mr. Kiffney is a believer in low-E glass, which stops some of the hottest rays of the sun -- if you're replacing the windows anyway. He doesn't, however, believe in replacing old windows just to get low-E glass.

There are also some somewhat modern, low-tech, active ways to handle air. Here's what you can do:

*Install a fan. You can get fancy and install a whole-house fan that exhausts hot air through the attic or eaves -- but it has to be sealed up in the winter to avoid introducing warm moist air which could cause condensation problems. You can also use simple box fans or window fans. They may not exchange the air at the same rate, but they will help.

The trick with fans is to pull air from cooler places. You may have to explore your house to find those places. Typically air will be cooler in north-facing rooms and in east-facing rooms after the sun rises. Basements usually have cooler air as well.

*Ceiling fans will make you feel cooler, because any air passing over your skin helps evaporate perspiration, a process that cools the skin. They also help even up room temperatures: On an especially hot day, mixing the air will result in a lower average temperature.

*Opening and closing doors and windows can have a big impact. Only open up a space if it facilitates the movement of hot air up and out. You may be better off to close up rooms you're not using during the day, and open them at night, when the air tends to be cooler. Mr. Kiffney says the lowest temperatures tend to occur between 3 a.m. and 6 a.m. "You may want to flush out the hot air during the night and pull in the 70-degree air."

*You may want to experiment with closing up the house during the hottest days, if you're not going to be home. It varies from house to house, but sometimes closing up the space will keep hot air out. Mr. Kiffney called this idea "counter-intuitive": It goes against the grain to shut things up in the heat. But if there's enough insulation and enough passive solar protection, you may be able to retain the cooler night air -- until you get home and open the house again to the cooler evening air.

Next: Tips on window air conditioners.

Mr. Johnson is construction manager for Neighborhood Housing Services of Baltimore. Ms. Menzie is Home Editor of The Sun.

If you have questions, comments, tips or experiences to share about working on houses, write to us c/o HOME WORK, The Sun, 501 N. Calvert St., Baltimore, Md. 21278. Questions of general interest will be answered in the column; comments, tips and experiences will be reported in occasional columns.

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