OK, class, put away your books and get out your pencils. This is a quiz. It's not a difficult one, but your answers may determine whether you can be comfortable in your old, un-centrally air-conditioned house this summer. Here goes:
1. Hot air _____. (Fill in the blank.)
2. Cold air _____. (Fill in the blank.)
Well, we said it wasn't hard. If you said "rises" for 1. and "falls" for 2., give yourself a nice, cold glass of your favorite soft drink.
While it's true that virtually everybody knows these simple physical laws, not everyone knows how to use them to vastly increase the comfort level of a home during hot weather.
You may be surprised how many of your home's architectural features are designed to facilitate heating and cooling. In Baltimore, for instance, rowhouses often have high ceilings, ventilating skylights at the tops of stairwells and operating transoms over all the doors. Some houses have interior air shafts with ventilating skylights at the roof and windows at the upper levels to let in light -- and pull out hot air.
These simple systems can be extremely effective if used properly. It's a good idea, when you're planning a rehab, to identify such features and design a floor plan that doesn't interfere with their operation.
The main purpose of these devices -- and it should also be the goal of any new features you install -- is to keep the air moving.
That means keeping hot air rising out of the top of the house and cooler air coming in on the lower levels.
This doesn't preclude using window air-conditioners. But they should be part of a house-wide system of air management.
Here are some tips for summer air-handling:
*Open ventilating skylights for the duration of hot weather. Keep transom windows open so hot air doesn't get trapped in a room. Open interior air-shaft windows. If the sun is beating down on the skylight/ventilating tube at the top, devise some kind of shade at the top, perhaps something like an upside-down parachute, to keep the sun out.
*Install window exhaust fans on the hottest side of the house (usually the south side) to help expel hot air and pull cooler air in from the cooler side of the house. If you have south-facing windows on more than one floor, expel it in both places. If you don't have two exhaust fans, keep the lower windows closed and pull the shades or curtains. The goal is not to pull in hot air.
*If you like ceiling fans, install them. The argument can be made that in a room with high ceilings, it's better not to stir the hotter air at the top of the room with a fan. However, you will feel cooler with air moving across your skin, and ceiling fans are good at that.
*Consider installing awnings on the hot side of the house. Awnings may be forbidden if you live in a historic district. Check the rules, and apply for a variance before adding awnings.
*A properly installed attic fan can be a boon in expelling hot summer air, but provisions have to be made to seal the ventilating opening completely in the winter. (In the winter you ZTC don't want warm moist air from the living space mixing with the cold air in the attic. That could cause condensation and "rain" in the attic.)
*If you're concerned about security with open windows, there are devices on the market that lock them into position. If you have double-hung windows, locking the top sash open a few inches may make sense. It will let rising hot air out, and, since it's protected under the window frame, may not let rain in as a bottom sash would.
*Window air-conditioners are great. It's 1992, and no one should have to struggle to sleep in 90-degree heat and 90 percent humidity. The only problem is if your house is in a historic district; you may not be able to install a window unit on the street side, where it shows.
There are a couple of ways to deal with this. One is to have a winter bedroom and a summer bedroom, much as our ancestors had summer kitchens and winter kitchens. If the summer bedroom is at the back of the house, you can chill it as you wish. If that's not an option, put the air conditioner in a window where it doesn't show and devise a way to pull it across the house.
Cold air tends to stay where you put it. That's why there's no problem having windows open for ventilation on the top floors while an air-conditioning unit is operating on the first floor. If the unit is on an upper floor, a little cold air may fall down the steps. But generally, the cold air won't get away.
You can, however, persuade cold air to move horizontally by installing an exhaust fan at the opposite side of the house, or by using a high-velocity fan in a doorway between cooler and hotter rooms. It may help to use an air-conditioner that's somewhat more powerful than you need, so there's plenty of cold air to pull around.
Next: Answers to readers' questions.
Mr. Johnson is construction manager for Neighborhood Housing Services of Baltimore. Ms. Menzie is a home writer for The Sun.
If you have questions, tips or experiences to share about working on houses, write to us c/o HOME WORK, The Sun, 501 N.
Calvert St., Baltimore 21278. Questions of general interest will be answered in the column; comments, tips and experiences will be reported in occasional columns.