Cubic feet per minute (CFM) measures how much airflow volume passes through a space in a minute. In HVAC, CFM airflow is important for determining the correct sizing and load capacity for your air conditioner, heat pump, and furnace.
Your HVAC system heats, cools, and moves air – that’s what the V in HVAC is all about – ventilation. Too much or too little airflow can impact your comfort but also can negatively impact your ductwork and HVAC system components.
Proper airflow helps your HVAC equipment run efficiently and helps ensure healthy air circulation and maintain even temperatures throughout your home. The right CFM can improve indoor air quality (IAQ) as well as comfort.
It depends on the size of your home. Larger homes will have a larger cubic feet per minute airflow need. A typical central AC unit or heat pump can produce an average of 400 CFM per ton of air conditioning capacity.
So, as an example, a 1,200 CFM requirement would mean you need a 3-ton HVAC system.
CFM is directly related to the air exchange rate or air changes per hour (ACH). This is a measurement of how many times the air in your home is fully replaced by fresh air or recirculated air each hour. In general, the higher the ACH, the better the indoor air quality.
ASHRAE, the American Society of Heating, Refrigerating, and Air-Conditioning Engineers, suggests in its Standard 62.2-2022 that residential buildings should have at least “0.35 air changes per hour, with a minimum of 15 cubic feet of air per minute per person” to ensure proper ventilation and acceptable indoor air quality.
ASHRAE also recommends exhaust fans for kitchens and bathrooms to help control pollutant levels and moisture levels. A ventilation system such as a whole-house ventilator may be recommended for homes with tight or foam insulation.
Here are some generally accepted recommendations for the ACH in various rooms in your home.
| RESIDENTIAL SPACE | RECOMMENDED ACH |
| Kitchen | 7-8 |
| Bathrooms | 6-7 |
| Laundry rooms | 8-9 |
| Living areas | 6-8 |
| Bedrooms | 5-6 |
| Basements | 3-4 |
HVAC professionals use this formula: CFM = Room Area (sq. ft.) x Ceiling Height (ft.) x ACH / 60(mins). You can also use this formula to calculate the necessary CFM for an entire house. The results will vary on the size of the home and other factors. If you really want to dig into the nitty-gritty, you can use this CFM calculator.
The required CFM for a room or house will depend on how many air changes are needed for adequate ventilation.
Your HVAC system can occasionally have airflow problems. The most common symptoms of airflow problems include:
Common causes of restricted airflow include:
The best way to ensure you get a properly sized HVAC system that provides the right CFM and keeps your home comfortable is to consult with your local Trane Comfort Specialist. To maintain proper airflow, you’ll want to schedule regular HVAC maintenance as well.
Discover the importance of correct HVAC sizing for efficient home heating and cooling. Consult with your local Trane dealer for expert guidance.
A ton in HVAC terms refers not to the weight of your central air conditioner or heat pump but to its cooling capacity. One ton corresponds to 12,000 BTUs.
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