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Discussion Starter · #1 ·
Hi - first-time poster here. I searched my question and didn't find the topic addressed previously.

My bathroom has a 70 CFM fan, but it's 122 cubic feet (10'10" ceilings in a 8.5'x10' room). Is it acceptable to add a second 70 CFM fan, or do we need one 130+ CFM unit?

Thanks much!
 

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Discussion Starter · #3 ·
Well, isn't that actually 920 ft³?
Yup, it is! I goofed - I should have said that what I've seen recommended is 122 CFM, minimum.

Would the existing duct need to be enlarged whether I go with a second fan or a bigger, single fan?

The contractor installed a 70 CFM fan and is proposing to install a second identical unit at his cost, so I'm really just wondering whether that scenario is as good as replacing the 70 with a 130+. I should have noted that first.

Thanks!
 

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Discussion Starter · #7 ·
I'm not sure where it's vented; it's brand new and was inspected by our local building department, so hopefully not into the attic (yes, there is an attic directly above it). I'd imagine it vents either through the roof or the side; both are pretty close to the fan's location.

Sounds like we'd need a bigger duct either way. Is a 2x70 CFM system going to be have the same effects as a 1x140 CFM fan (assuming both are equally well vented)?

Thanks again!
 

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Discussion Starter · #11 ·
Some good questions that I can actually answer:

1. How much air is getting into the bathroom?
A decent amount; there's space for a transom window above the door, but it hasn't yet been glassed-in, so it's totally open (probably ~2sf).

2. What kind of showers are happening?
One of us takes what I'd call normal temp showers, the other takes very hot ones!

3. What is the reason I want a larger fan?
It's very steamy in the bathroom for a long while after any kind of shower.

Thank you guys!
 

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Discussion Starter · #13 ·
No, I haven't. I did the calculation I found on Home Depot and another site, and both recommended at least 122 CFM for our 920 cf room (10'10" ceilings), which made me think our 70 CFM fan is very inadequate. Do you think it should be doing the job?
 

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Discussion Starter · #16 ·
I think 70 isn't enough because the bathroom is very steamy for a long time after a shower (an hour?). That's a pretty general statement so I'll add that it's much steamier for much longer than any other bathroom I can recall having showered in.

Installing a timer might be problematic: the fan is within a can light unit that's controlled by one switch, so the timer would also leave the light on/turn it off at potentially inconvenient times.

Thanks!
 
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