How to calculate ventilation rates

Updated April 17, 2017

Proper ventilation is required to eliminate toxins in the indoor air from off-gassing furniture and gas appliances. Air movement is also important to decrease the feeling of a stuffy room. On the other hand, if your home has too much ventilation, it will be draughty and energy inefficient. According to the Environmental Protection Agency (EPA), most ventilation ducting supplies homes with a combination of outside air and recirculated air. The rate of air circulation is expressed as cfm, or cubic feet per minute. Use calculations to find the minimum amount of ventilation to keep your home healthy, comfortable and energy efficient.

Identify parts of the calculation. r= 60a/V

"r" equals the air change rate per hour. "a" equals the supplied air flow into the room (cfm). "V" equals the rooms volume (cubic feet or cf).

Find blower door testing equipment to get accurate numbers (in cfm). Seal an exterior door using the blower door and turn the fan on. The meter will give you the air flow ("a").

Replace your numbers for the air flow "a". Enter in the volume of the room for "V".

Multiply your air flow by 60, then divide by the room's volume to find the air change rate per hour ("r").

Things You'll Need

  • Blower door test
  • Paper
  • Pencil
  • Calculator (optional)
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About the Author

Mercedes Martinez is an eco-designer focusing on renovations. She has a degree in interior design and a minor in architecture. Recently, Martinez has been enjoying exploring her writing skills that have developed her passion for design.