Ventilation fans have become an increasingly important as the construction standards for building insulation and vapor barriers has made homes tighter and tighter. This has increased the energy efficiency of these buildings significantly, but has also brought about issues with indoor air pollution, mold, and mildew. Part of the control of these issues is through the use of ventilation fans and it is important to know what ventilation fans should be installed and the correct method of installing them.
CFM (cubic feet per minute) is a way of measuring the amount of air that it takes to fill a space, in this case, a room. Ventilation fans have to be able to pull out the moist air from a bathroom, which requires 8 air changes per hour, or kitchen stove, which requires 100 CFM for every 10″ of stove width, in order to properly remove the moist air from the home.
Calculate the volume of the space (length x width x height) and divide this volume by 8 (the number of air changes per hour needed for a bathroom. For example a bathroom that is 8’x8’x8′ = 512 cubic feet square of volume. 512/8 = 64 so you will need a 64 CFM ventilation fan that will run for approximately 20 minutes after you are finished with your baths and showers.
Stove ventilation requires a much higher CFM at 100 CFM per 10″ of stove width. So if you have a standard 36″ stove, 36/10 = 3.6. 3.6×100 = 360 CFM. This is a fairly low to moderate setting on a stove ventilation hood. For larger stoves, more industrial ventilation hoods may be required.
Bathroom fans must be ventilated to the exterior of the building. The best practices have the ventilation pipe going through the roof or the sidewall.
Stoves are not required to be ventilated to the exterior for electric appliances or gas appliances, however, it is a good practice to do so for either appliance to pull grease and carcinogens out if the air.
Choosing ventilation fans is very important to the health and integrity of your home. Use these formulas to determine CFM size and if you have bathroom of kitchen moisture issues, see if your fan is up to the task.