Comments on: 5 Reasons Bath Fans Have Such Poor Air Flow

By: David Butler

David Butler — Fri, 26 Sep 2014 06:45:07 +0000

@John, even though RH may be
@John, even though RH may be higher outside than inside, even 100%, the dew point (which is what matters) of a bath exhaust is usually much higher than the outside dew point, especially in winter. The problem is when wood surfaces in the attic are colder than the exhaust air dew point... you get condensation.

Exhausting a bath fan through a soffit as you describe may be OK as long as there's no possibility of feedback.

By: John

John — Fri, 26 Sep 2014 02:37:46 +0000

What about when the moisture
What about when the moisture is high in the air outside anyway, such as on a rainy day the moisture levels outside could be at 96% humidity +. And if the soffits are open, isn't this humid air being exchanged into the attic, especially if there's a gable or ridge vent pulling the soffit air through? Isn't having a bath fan going directly into the attic doing the same thing, putting humid air into the attic? Or, even if the bath fan was vented through a soffit, that is separated by 5 feet on either side away from other soffits, shouldn't this solve bath fan air going into the attic?

By: Will

Will — Wed, 18 Jun 2014 19:32:41 +0000

I may have missed it, but the
I may have missed it, but the most common reason I find in my area is that people, have installed replacement motors and they have them in backward. The fan blades spin the wrong direction and no air is pulled out of the bathroom.

By: jerry

jerry — Fri, 28 Dec 2012 20:24:18 +0000

Can i drop down a foot to
Can i drop down a foot to exit the room to outside,I am in the basement and do not want to drill through the header

By: Chris

Chris — Thu, 25 Oct 2012 22:24:44 +0000

I just installed a 135 CFM in
I just installed a 135 CFM in-line ventilation fan for my 85 sq ft bathroom, this fan replaced a 45 CFM ceiling mount fan and light. I removed the 45 CFM fan & motor from the housing and left the ceiling cover and light in place in spliced the in-line fan in the duct work in the attic. I have a 1" undercut at the bottom of the bathroom door and the duct has one elbow at at the ceiling vent housing and then runs about 9' straight out the back of the house. I figured I would have no steam issues in the bathroom with this set up, however, I turned the shower on, let it run 20 minutes, walked in the bathroom and it was completely steamed up, walls and ceiling dripping with moisture. The duct is clear, no obstructions..

What could the problem be? I'm really at a loss and frustrated, I'm tired of having to wipe the walls down after every shower!

By: Mike Coles-Webb

Mike Coles-Webb — Mon, 22 Oct 2012 11:10:45 +0000

Run new 4 inch duct and a new
Run new 4 inch duct and a new 4 inch vent. Insulate the duct.

By: Jonathan

Jonathan — Sun, 30 Sep 2012 17:33:48 +0000

Great info. Wonder if anyone
Great info. Wonder if anyone can help with a problem I’m having: I’m replacing a small bathroom fan which didn’t work well with a higher cfm version. The old ductwork is about 5′ and straight, but it’s only 3″ around while the new fan has a 6″ opening with a 6″ to 4″ adapter. Is it safe to put a 4″ to 3″ adapter on and use the existing duct or do I need to run new 4″ ducting? It’s a small bathroom. Thanks!

By: Cameron T

Cameron T — Mon, 03 Sep 2012 22:31:31 +0000

One more scenario to consider
One more scenario to consider: ducts could be perfect to outdoors with no obstructions, plenty of makeup air is available, and the poor fan still not move much air. How?

That cheap little plastic damper on the discharge of the fan has been stuck closed from installation due to drywall texture or paint overspray. Seen that happen a lot.

By: Allison Bailes

Allison Bailes — Mon, 03 Sep 2012 22:03:10 +0000

Gordon T.:
Gordon T.: I seem to recall responding to your question about wall-mounted fans somewhere (LinkedIn) and probably said they're OK if they don't go through a building envelope wall. I did write something about mineral wool this summer. Did you see it?

Green Curmudgeons, Architects, and Outlawing Batt Insulation

Barbara W.: You'll have to have someone determine why they're not pulling air out of those rooms. It could be the fan, the duct, the wall cap, or any combination. Why do you have a fan in the laundry room, though? That's a bit unusual and could cause problems, depending on what else is in there.

By: Barbara Weskot

Barbara Weskot — Mon, 03 Sep 2012 21:55:34 +0000

Please Help, I have three
Please Help, I have three vents, two in the bathrm. and one in the laungry rm. They work But they do not pull the air out the rm so they are not functional. The house has no basement or attic. What can be done to fix this problem. Thanks