Bathroom fan size
Shawnnixon1
| Posted in General Questions on
My bathroom size is 10.3×10.3 with 8 foot ceiling. Current have 50cfm fan which is almost useless and loud. I have a stand up shower, toilet and freestanding tub (barely use).
My exhaust fan duct goes to a soffit in the roof. The distance is about 6 feet or so.
how much CFM fan do I need?
Current duct size is 3”. Should I change to 4 or 6”?
Bathroom fan should I get 110cfm? Is 150 overkill?
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Replies
The IRC requires 50 cfm intermittent or 20 cfm continuous for bathrooms, regardless of size.
I recently installed a 110 cfm fan in my bathroom, which is a little smaller than yours, and it clears the air quickly. It's a Panasonic Whisper series and it's nearly silent. I used (and recommend) rigid 4" ducting with as few turns as possible.
Here's how I recommend venting, when possible: https://www.finehomebuilding.com/2018/03/01/bath-fan-venting-cold-climates
Mine is not central, its a separate fan with a switch.
So is mine; I'm not sure what I wrote that made you think otherwise.
Sorry how do you have intermittent or continous fan working in the bathroom ?
Intermittent is the typical kind--you turn it on when you're using it, and turn it off when you're not using it. Or sometimes it's on a timer.
Some models are available than run continuously on low speed. They are code-compliant for whole-house ventilation, but they are still just a single fan in a bathroom.
Not OP but building my own home in Zone 5 currently. My master bath is going in a 10ft wide by 12ft deep dormer, but the wife wants the toilet to be walled off separately as a water closet type deal. Is there a way to use only one fan or will I need to buy one for the double shower and one for the toilet or in other words, can I somehow only have one exhaust on my dormer gable or will I need two?
Eric,
Either an inline or exterior mounted fan can exhaust both.
Shawn,
Many of the Panasonic Whisper fans have two or three speeds you can choose, allowing you to see which works best for the space once installed.
Which duct size though
Shawn,
4"
4” then I’d have to go 110cfm fan since the 130/150cfm has 6” port on the fan is 110 good for 10.3x10.3 bathroom with 8” ceiling?
Shawn,
Yes. I'd use the 80/110 fan. An 800 cuft space without a jetted tub shouldn't need more than that to clear very quickly.
You say “almost useless” what does that mean to you?
If your complaint is that mold is growing in the bathroom that is one thing but if the complaint is the corner of mirror is foggy after a 30-minute shower that is something else.
Even the best fans do not move much air so have realistic expiations.
If the fan is a few years old and was acceptable taking it a part cleaning and oiling it could be worth a try.
Yes, some of the builder grade fans were always junk and hopeless, I would likely upgrade.
If you do upgrade the fan, make sure the new ductwork is steel pipes and not flexible plastic stuff.
Walta
The current fan is builder fan 50cfm for a bathroom 10.3x10.3. No mold growing but it doesn’t remove moisture or humidity out of the bathroom even when its on for 45min
They used flexible duct and the run is about 6 feet
I have no data but my guess is most people only use the fan for smells and not so much for moisture.
Is your winter time indoor humidity over 50%? That is when I would expect excess moisture to be the biggest problem.
If the bath is a little muggy after a shower, I do not see it as a huge issue.
Given how muggy it is in my climate running a fan would remove precious conditioned air that will be replaced with hot muggy air pulled in thru the gaps and seems likely to increase my indoor humidity.
I might change the fan just because I find noisy poor-quality equipment annoying.
Understand a perfect flex duct installation flow poorly compared to rigid and flex duct is mostly installed very poorly. You may find this article interesting.
https://www.greenbuildingadvisor.com/article/should-flex-duct-be-banned
Walta
Walta,
Now it's not necessary to control humidity in bathrooms? That a novel idea I've never heard put forward.
What about semi rigid? I
Get 100 cfm or larger is fine, if you can't increase duct diameter stick with 4 inch. Don't do 3 inch for a full bathroom. Too big a fan can get loud. Get 1.5 sones or less for quiet operation and energy star rated plus continuous-use rated is a smart choice, read the product specs.
The smoother the duct the better the airflow, if you can't use rigid metal duct, use semi-rigid metal duct, or a combination of the two. Pull it as tight as possible and it will work well, avoid hard bends as much as possible. Seal any duct joints and seal fan body to ceiling drywall from attic space if possible.
examples of products to use.
https://www.homedepot.com/p/Rubber-Cal-Aluminum-Flex-280-Compressible-4-in-x-9-84-ft-Flexible-Duct-01-226-4/327741897?source=shoppingads&locale=en-US&srsltid=AfmBOooWiEhrx8mdmqm2L1e6M4WKBBDTS0JPJwW1Lk7jQb3WSYWVMEVyKvk
https://www.lowes.com/pd/Utilitech-Ventilation-Fan-1-5-Sone-100-CFM-White-Bathroom-Fan-ENERGY-STAR/1000233797?user=shopping&feed=yes&srsltid=AfmBOorlz77jQzPrEsLxYsZSM-eHbwFk0CWzjwBHTmUTdDsM6Lulx772HqI
“What about semi rigid?”
You want a steel tube and not a spring covered in plastic.
The spring always has some drop and the uneven surface restricts the flow.
Do you have a link to semi rigid? Sound like flex duct renamed.
Walta
I have a similar question about choosing a bathroom exhaust fan, but for a very different bathroom scenario. Currently, there is no fan. One wall is about 12"–thick, made of adobe brick plus cement stucco outside and gypsum plaster inside. So I have the potential for a very short, straight duct run through the wall. There is not a convenient location for a normal-sized exhaust fan. I am thinking of mounting the fan fairly low on the wall, perhaps 12" above the floor, to one side of the toilet, out of foot traffic. If possible, I would like to recess the fan into the adobe wall.
Are there exhaust fans designed for this kind of situation? Can anyone suggest specific models? Could I use a 4", 5", or 6" muffin fan, of the sort that are used to cool computers? Some of them are quiet and have the recommended bathroom exhause CFM ratings.
lutro,
It might be easier to use a through-wall fan, rather than trying to mount a typical bathroom one. Something along these lines: https://www.wayfair.ca/home-improvement/pdp/broan-nutone-180-cfm-bathroom-fan-brn1814.html
Thank you, Malcolm!