Air balancing involves testing and adjusting your HVAC system to optimize distribution of air to each room of your home. Air balancing can improve air circulation in your home and the overall performance of your heating and air conditioning system. Balancing also helps even out temperature variations between rooms and is often necessary after you have moved into your new home and established your living routines.

Air balancing can be done by a licensed professional or on your own as part of your regular home care and maintenance, and may need to be revisited with a change of the seasons. This guide walks you through the process. 

What You Need

• Access to your registers. Make sure you can access your registers. You may need to move some furniture. If the registers are high on the wall or in the ceiling, you may need a step stool.

• Thermometer. You’ll need to check the temperatures in each room. A portable thermometer should be sufficient. There are also many thermometer apps available.

• Time. Air balancing requires periods of time for each adjustment, so be sure to allow yourself to dedicate some time to your balancing effort.

What to Do

1. Adjust your registers. Adjust all your registers by opening and closing the dampers (valve or plate that regulates how much air gets through), adjusting the air flow at each point.

   • If you are balancing your system for the first time, we suggest opening your registers all the way to start.

   • If you are fine tuning your system (using winter as an example), adjust the registers based on how the room feels. In rooms that are cold, open the supply registers all the way. In rooms that are too hot or where warm air is coming out in great force, close the supply registers partially (never all the way).

2. Turn your system on. Turn on your system and allow it to run during the balancing process. Set a temperature setting that will keep the system in either full heat or cooling mode whichever is appropriate for the season.

3. Wait. Give the system at least 1 hour to work.

4. Check room temperatures. Using thermometers in each zone or room, determine what adjustments need to be made to each register. Based on sun exposure, window coverings and overall orientation, it is normal to have a 3-5-degree variation between rooms.

5. Adjust registers and repeat. Based on your temperature readings or overall room comfort, adjust your registers open or closed and repeat your readings in an hour or so. Continue to adjust your registers in small increments until each room reaches your desired comfort level.

Tips and Recommendations

• Supply duct dampers. If your supply ducts have a damper, they must be adjusted as well.

• Clean filter. Make sure your filter is clean and serviceable. Dirty filters will cause improper system operation and make the balancing procedure ineffective.

• Clear vents. Make sure that air can flow through your registers and vents, and move any furniture that could be restricting air flows.

• Patience. When balancing the system, allow plenty of time to pass between adjustments.  

• Registers near thermostats. Registers close to a thermostat require special attention. If the register is putting out cold air directly on the thermostat, it will read the temperature as lower than it will feel in the rest of the room. The same is true when the heat is on. It will read a higher temperature with warm air blowing on it. To combat this, when the heat is on, close a register that is near the thermostat to lower the temperature near the thermostat and, in effect, increase the temperature in other rooms. When the air conditioning is on, close a register near the thermostat to raise the temperature near the thermostat and, in effect, lower the temperature in other rooms. 

• Air temperature vs. home temperature. While air temperature changes quickly, it can take some time to warm or cool your home—the temperatures of the floors, walls and your home’s contents change slowly, and those materials have a big impact on how the room feels. If your home has gotten uncomfortably hot or cold, give it a day or so for the temperature to stabilize before doing the balancing procedure.