Room size in a house and the specific volume of HVAC airflow into that room aren’t an accident. For optimum heating and cooling efficiency, the amount of airflow entering rooms through supply vents is a carefully calculated figure based on room size. This process, called air balancing, is critical to maintaining optimum comfort and low operating costs.

Room size is expressed in square footage, while the volume of conditioned air entering that room is measured in cubic feet per minute (CFM). Here’s what happens when the CFM doesn’t match square footage:

  • If airflow volume is too low, temperatures in the room may be too cold in the winter or overly hot in the summer.
  • If airflow volume is too high, excess heated or cooled air is pushed out of the house through structural cracks and gaps. Energy is wasted and HVAC operating costs rise.
  • When airflow volume into one or more rooms is too low or too high for the respective room size, the entire system may be unbalanced. Some rooms in the house may receive insufficient airflow to stay comfortable while other rooms get too much.

A Balancing Act

The air-balancing process involves precisely measuring airflow into each room at the individual supply vent using an airflow hood. In most homes, the amount of air entering the room should equal 1 cubic foot per minute for each square foot of room size.

  • Where the airflow volume is insufficient, duct leakage may be an issue. Alternatively, an internal adjustment damper inside the ductwork may have closed, restricting room airflow.
  • If airflow into one or more rooms is excessive, supply vents in other rooms may be closed or obstructed, or an internal damper may be open too wide.

Effective airflow balancing usually requires measurement of airflow into all rooms in the house along with readjusting internal dampers in proper sequence to ensure that the CFM of airflow matches the square footage of every room.

For more information about the important relationship between room size and airflow, contact the professionals at Mowery Heating, Cooling and Plumbing.