Sensible Home: Adjust Air Duct Dampers to balance room temperature

Posted by James Dulley on 10th Feb 2014

Dear Jim: We have central air conditioning, but have a problem keeping all the rooms evenly cool. Someone is always too hot or too cool. What are some simple methods to balance the temperatures throughout the house?

– Jason F.

Dear Jason: The problem you are experiencing is not uncommon even for the newest air-conditioning systems. Unless you install an expensive zone control system, your air conditioner can respond only to the temperature of the room where the wall thermostat is located.

Numerous factors determine how much cooling, and therefore the temperature, various rooms throughout your house need. These include the number and orientation of the windows, whether it is on the first or second floor, the activity level in the room, the length of the duct leading to it, etc.

The simplest, no-cost method to control the various room temperatures is to adjust the duct dampers. These are adjustable baffles near the indoor blower unit inside of the ducts leading to the individual rooms or groups of rooms. By closing one, more cooling air goes to other warmer rooms.

Most duct systems have them. Look for a handle on the side of the duct. Typically, when the handle is lined up with the duct, the damper is wide open. Start by closing a damper halfway (turning the handle 45 degrees) in ducts leading to the rooms that are too cool and making sure the others are fully open. You will have to change the settings for winter heating.

It takes an hour or so for the room temperatures to change. Check the rooms and readjust the dampers until you get the desired result. You may have to shut some almost completely, especially ones with short ducts on a lower floor. Don’t close more than half of them or it may cause too much air flow resistance for good efficiency.

If this method does not provide adequate temperature balancing, consider installing duct booster fans. These small fans mount in the ducts to the warm rooms and force more of the air-conditioned air to them.

These fans are sized to fit standard round and rectangular residential ducts. They can be controlled in different ways. The simplest ones sense when the main blower comes on and they run automatically at the same time. Others have their own thermostat to determine when they run. Generally, it is best to have an experienced contractor do the installation for you.

Another simple do-it-yourself option is to install a register booster fan. This small rectangular fan mounts over the register cover in the room and is plugged into a standard electrical wall outlet. The small fan uses only about 30 watts of electricity. They are adjustable to come on only when more cooling or heating is needed in that room.

Dear Jim: I do not want permanent window film on a small kitchen window, but I want something to block the glare. How effective are cellular shades and can one easily be removed during winter to get more sun? – Carol D.

Dear Carol: Translucent cellular shades are ideal for eliminating the glare from a window and the double-cell ones also add some insulation value for energy efficiency.

Completely removing the shade allows more wintertime solar heat indoors. SimpleFit cellular shades ( are the easiest to snap in an out of the tiny brackets. They are custom-sized, and the brackets are adhesive-backed for quick installation.

Send inquiries to James Dulley, The Forum of Fargo-Moorhead, 6906 Royalgreen Drive, Cincinnati, OH 45244, or visit