How to Determine How Much CFM a Room Needs for Heating

by David Robinson
Heating should always be combined with adequate ventilation.

Heating should always be combined with adequate ventilation.

Installing the right heating system in a room is important, and not just for the comfort brought by a pleasant temperature. Heating a room can help to eliminate dampness, but only if it is also ventilated correctly. Poor ventilation results in an increase in humidity, and that can encourage mold to grow on everything from walls to carpets. The secret is to ensure a steady flow of air through a room while it is being heated, keeping the temperature constant but preventing a buildup of moisture. The volume of air that must be circulated through the room is measured in cubic feet per minute -- CFM -- and determining the correct volume is the key to a successful heating system.


Measure the length, width and height of the room, using a tape measure. Round all the values up to the next full foot, to simplify the calculations. For example, if a room length is 17 feet and 7 inches, round it up to 18 feet.


Multiply the three values together to determine the volume of the room in cubic feet. For example, if the length is 18 feet, the width is 12 feet and the height is 10 feet, the room volume is obtained from the equation volume = 18 x 12 x 10, giving a room volume of 2,160 cubic feet.


Multiply the volume of the room by the number of times the heated air is to be changed every hour. The result is the volume of heated air that passes through the room in one hour. For example, if the air is changed six times every hour, multiply the volume of air determined in Step 2 by six. Using the example data from Step 2, the result would be six times 2,160 cubic feet, or 12,960 cubic feet of air passing through the room per hour.


Divide the value obtained in Step 3 by 60, the number of minutes in one hour. The result is the volume of air that must be passed through the room every minute. For example, 12,960 divided by 60 equals 216, so 216 cubic feet of air must be fed into the room every minute. The room requires 216 CFM for heating.

Things You Will Need

  • Tape measure
  • Calculator


  • The number of times that the air in the room is replaced can be determined with precision only by reference to the output capacity of the heating system, the desired temperature of the room, the temperature of the air entering the room and the heat-loss characteristics of the building structure. In practice it's a value determined by trial and error, by using the room and deciding whether or not it is comfortable.


  • Balancing a heating system can be a complicated process. Atmospheric conditions change constantly, and the heating system must respond accordingly. If in doubt, consult a qualified heating engineer before adjusting the system.

About the Author

David Robinson has written professionally since 2000. He is a Fellow of the Royal Geographical Society and the Royal Meteorological Society. He has written for the "Telegraph" and "Guardian" newspapers in the U.K., government publications, websites, magazines and school textbooks. He holds an honors Bachelor of Arts in geography and education and a teaching certificate from Durham University, England.

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