Going from air conditioning to heating, and back again, is common in North Georgia’s changeable weather. The problem with this is the fact that chilled air behaves very differently than heated air.

You don’t need to be an HVAC (heat, ventilation, air conditioning) expert to check on some of the basics in your home. The first, and most important, factor in operating the HVAC system efficiently is insulation. Using plastic window covers, taping windows shut, and similar measures is only an emergency solution. It’s much more effective to make the house thermally inert with ceiling and floor insulation.

In winter, the problem isn’t cold that “comes in.” It’s heat leaving the house. It does so by escaping through the ceiling and the roof because warm air has a tendency to rise.

Heat ducts mounted in the ceiling aren’t the most useful type because cool air can accumulate around the occupants’ feet. Warm air tends to spread better if the ducts are on the floor. Keep items away from them to avoid heating furniture instead of the room.

If the ducts are in a high traffic area, especially on carpeted floors, dust can be distributed through the whole room, causing discomfort.

The worst kind are air returns mounted in the floor. The air being drawn down into them will carry with it pet dander, dirt, dust, pencils and other small objects getting near them. The smallest particles will eventually end up in the air again that we’re breathing.

Today’s air ducts are mostly of the flexible kind, and relocating them is often within the abilities of the average homeowner.

Both heating and air conditioning tend to make room air drier. Air that’s heated has a natural tendency to decrease in humidity.

When the heat is running a lot on cold days, this may require using a humidifier.

Cooling the air should make it get more humid, but the HVAC system compensates by actively removing moisture from the room. Dry, cool air is heavy and lazy. Instead of seeking the ceiling, it wants to escape by sinking through the floor, and creeping out of door thresholds.
In air-conditioned regions, floor insulation applied from a basement or crawl space is therefore important. In all HVAC questions, it helps to remember: Warm air and moist air want to rise. Cool air and dry air want to sink.

Rudi Kiefer, Ph.D., is a professor of physical science and director of sustainability at Brenau University. His column appears Sundays and at gainesvilletimes.com.