Bathroom exhaust fan size


  #1  
Old 04-27-05, 07:52 AM
sorensenj's Avatar
Member
Thread Starter
Join Date: Oct 2004
Location: Westcentral Wisconsin
Posts: 48
Upvotes: 0
Received 0 Upvotes on 0 Posts
Bathroom exhaust fan size

Is there a rule of thumb as to how to size an exhaust fan for a bathroom? Thank you!
 
  #2  
Old 04-27-05, 08:23 AM
Doug Aleshire's Avatar
Member
Join Date: Feb 2002
Location: United States
Posts: 4,455
Upvotes: 0
Received 0 Upvotes on 0 Posts
sorensenj,

It's not that I always want to use larger fans but depending on the use and size of room, it is essential to avoid problems. I have had clients use 50 - 110 cfm units and when the family takes long hot showers, they are having problems.

It's an issue that needs to be addressed and when one installs a steam shower bath, heated whirlpools, it's even more critical.

Trouble with fan sizing, they don't take into account what is acually in the bathroom, like 2 sinks or one, like 3 fixture bath, 5 fixture bath and how many are in the family. These factors are more important than the actual size of the room. To top it off, then you get a house full of company, then what? The other issue is that if a family is taking more showers than baths, more moisture is emitted into the room, again, this is more important than room size.

Another issue is vaulted ceilings - or taller than 8' is also an issue so this is another factor. 9 or 10 ft ceilings create more need for larger fan size.

I do agree though that trying to get a quiet fan is the hard part as they are more expensive but what is more important?

Good site for bath fan sizing,

http://steamsaun.com/panasonic/sizing.html

Good sites to look at sones

http://www.broan.com/product-categor...CategoryID=501

http://www.positive-energy.com/pages...nCeiling2.html

I prefer Panasonic but Nutone-Broan are just as good. It's a matter of quality versus price, as always.

Hope this helps!
 
  #3  
Old 04-28-05, 06:31 AM
P
Member
Join Date: Feb 2003
Posts: 141
Upvotes: 0
Received 0 Upvotes on 0 Posts
I think bathroom rule of thumb is 8 air changes per hour. So 7 ft x 10 ft x 8 ft ceiling room would be 560 cubic feet x 8 = 4,480 cubic feet per hour / 60 = 75 cubic feet per minute exhaust fan minimum. I'd use a larger one.

Floor area multiplied by 1.1 gives a good estimate, but only for 8 ft ceiling height.

I just picked the numbers out of thin air for the example - substitute your own room dimensions. If you have a steam shower or equivalent putting out a lot of humidity I'd think about doubling the exhaust rate.

When you're putting it in just don't restrict the duct. If its 4" then don't reduce it 3". The fan won't be able to push the same cfm through the smaller pipe.
 
  #4  
Old 04-28-05, 11:53 PM
sorensenj's Avatar
Member
Thread Starter
Join Date: Oct 2004
Location: Westcentral Wisconsin
Posts: 48
Upvotes: 0
Received 0 Upvotes on 0 Posts
Thanks for the advice and links. I can always count on DIY for straight answers.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: