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Proper CFM rating for a bathroom fan

4K views 15 replies 8 participants last post by  plummen 
#1 ·
Hello all,

I'm going to be installing a new vent fan in my bathroom in the next week or two. I've read that the necessary CFM rating should be about 1-1.1 times the square footage of the bathroom. I don't remember the exact dimensions of my bathroom but it's approx. 50 sq ft.

My question is, when it comes to the CFM rating, is more always better or would I just be wasting my money by getting a higher CFM model than the above rule of thumb says that I need? Or is that rule of thumb even accurate?

Thanks in advance.
 
#2 ·
If my memory serves me correctly it's the total cubic square footage of bathroom, measured width x's hiegth x's depth divided by 8, the number of times it should be able to refresh the air in the room per hour. That's the cfm you will need.

I'm pretty sure you need to re-measure the space, my non-walk in closet is bigger than 50 square cubic feet and I barely fit in there.

And research "sones" as well, noise level of fan.
 
#4 ·
Thanks for the link, Doc.

The suggestions I've seen otherwise have been relative to square feet. The volume of my bathroom is probably in the neighborhood of 400 cubic feet if I had to venture a guess. It looks like the recommended CFM rating using either formula would be a little over 50.
 
#6 ·
Thanks for the link, Doc.

The suggestions I've seen otherwise have been relative to square feet. The volume of my bathroom is probably in the neighborhood of 400 cubic feet if I had to venture a guess. It looks like the recommended CFM rating using either formula would be a little over 50.
The choices are very limited, we recently ( 09') rebuilt from a house fire, and I did alot of research and found that regardless of the size of the bath room, it came down to four fans to chose from, 50, 70, 80, and 110 cfm. i went with the 110 cfm and have not regretted it one bit. And yes it was over kill, but it gets the moisture, and the odor out in a hurry.
 
#13 ·
I think the actual energy (amps) used by the larger fan would be insignificant. More significant may be the cost of conditioning the air that you are expelling thru the bath fan. I'm thinking that once the room is dry, it's dry. I just installed 90 CFM fans in my bathrooms. One has had none for 50 years. Just a window. (The other bathroom is new construction and hasn't been used yet.) The difference is noticeable. I also put timers on the fans. Usually set the timers to run for 10-15 minutes after the shower is turned off.
 
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