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How to fix warm air heating

Balancing and maintaining a forced-air heating system

Manually adjusted dampers in the ducts of a forced-air system let you regulate the amount of warm air entering a room. If some rooms are cold and others overheated, balance the system by opening or closing the dampers.

Look for dampers at the beginning of branch ducts leading from a main duct (or, in some systems, from the hot-air plenum) to room registers. Follow a branch duct’s path to determine which room it heats; or close a damper to see which room gets cold. Label the damper once you’ve identified it. A damper is closed when its handle is at right angles to the duct; it’s open when the handle is parallel to the duct. Secure a damper in place by tightening its locknut (if any].

Balance the ducts on a cold day. Fully open all dampers and registers.

Set the thermostat at normal room temperature and let it operate the heating system for at least 3 hours. Partially close the damper in the duct leading to a room that overheats. Wait an hour, then see how the room feels; check its temperature with a thermometer held 4 feet above the floor. Open or close the damper as needed; check the room again after an hour. Working from warm to cold, repeat the procedure in each room. Because adjusting air flow in one duct affects the others, fine-tuning the system may take several days. If after balancing the ducts, some rooms remain cold, try increasing the speed of the furnace blower.

Maintenance

Periodically vacuum the room registers using a crevice tool. Once a year, inspect ductwork for leaks; seal them with duct tape.