What Does CFM Mean?
CFM, or cubic feet per minute of air flow, is a whole house fan rating useful in sizing the proper whole house fan. It is the measurement of the air volume that is moved by the fan blower inside the whole house fan.
When you are trying to decide the right size fan, you will look specifically at the CFM as compared to the size of room and the type of air flow you are looking for.
How is it Useful for Whole House Fans?
When you first begin shopping for a whole house fan, the biggest confusion is often choosing the right size. The size of your home and the rooms to be cooled off make a difference when sizing your whole house fan.
Instead of using the guesstimating approach, it helps to have a solid measurement that can be used for getting the right size. While there is also a specific formula, the basic consensus is that the CFM rating for the fan should be about 2-3 times your home’s square footage.
First, you’ll need to calculate the square feet of your home in cubic feet, then use that to figure out what CFM you are looking for.
Doing the Calculations
To get down to the actual calculations of the CFM rating, start with the square footage of your home or the area you intend to cool with the whole house fan. You most likely already know the square footage, but you can also get this measurement if you need to.
Next, multiply the square footage by the height between the floor and ceiling. Take this number and multiply it by 60 (or 30), depending on how much air power you want. Finally, divide that by 60 minutes in order to get the cubic feet per minute. This will be CFM measurement you want.
(Square Feet______ x Room Height______) x 30 or 60 / 60 = CFM Needed
Your Whole House Fan Cooling Options
You have two main options with the CFM ratings of whole house fans, including efficient cooling and breeze effect cooling.
● Efficient cooling is a great option for those with 1.5 to 2.0 CFM for square foot of living space. This is a more cost-effective cooling when you want your entire home cooled but don’t want to use as much energy. With a fan rating of 3,000 – 4,000 CFM, you will have a constant stream of air going through all of the rooms, ceiling, attic, and walls.
● The other option is the breeze effect cooling, for 2.5 to 3.0 CFM per square foot of living space. If you like to have a steady breeze blowing through your home, similar to what you experience with a fan pointed at you, look for a fan rating of 5000 – 6000 CFM.
Regardless of the size of whole house fan you opt for, you’ll need to have proper roof ventilation.