Bath fan problem. Need a solution.

8 years ago

This is a brand new house. It's actually a log cabin. Bath fan is on a sloped ceiling and drips during showers. The builder originally thought it was due to condensation and the cold but it drips when it is not cold to. It doesnt drip when my husband takes showers but when I do since i am in their longer and probably have the water hotter. The fan is 70 cfm. Foremen thinks that all the steam is funneling up to the fan and the fan can't handle it and the sloped ceiling is causing the fan to sling the water onto metal housing and then dripping out the low end of the fan. He said if we install a higher cfm fan it requires a 6 inch duct. What is there now is 4 inch which goes to a vent in the soffit which is at the front of the house. Foremen said he doesn't think the 6 inch ducting would be able to make the turn into the vent at the soffit. That the ducting would have to just end in the soffit which doesn't sit well with me. Theres got to be fans that are higher cfms that still have 4 inch ducting that would work. I just don't know how much cfms would be adequate. He talked about making the ceiling in the shower flat and installing an additional fan in the shower and both fans would turn on with one switch. I don't like this idea either. I've included pictures of the situation. If anyone has any ideas or even suggestions for a fan please let me know. The bath fan currently there is some piece of junk Broan which I'm thinking is part of the problem. Here's the bathroom dimensions and photos:

Featured Answer

MongoCT

8 years ago

The outlet for the bath vent and the intake for the roof's soffit-to-ridge vent are located next to each other.

An issue with a bathroom exhaust vent located in the soffit, combined with a roof vented by soffit-to-ridge venting, is the humid air that is exhausted from the bath fan can be brought back into the structure through the roof vent assembly.

Is that a cathedral ceiling? Is the duct running down to the soffit via a rafter bay? Or is there an attic above the bathroom, and the existing ductwork is accessible?

They should be able to do a test to see how much air the fan is actually moving.

I'd look at the existing duct as well. How long is the run? How many turns? Any choke or pinch points? Most manufacturers have design sheets showing the maximum effective duct length allowed for their fans. Each 45 turn, each 90 turn, counts as so many feet. Add it up and see if it's the duct layout that's killing the flow.

If it's flex duct, I'd have it replaced with hard-wall, that'll reduce turbulence within the duct and improve airflow.

I'd also make sure the duct is insulated.

If you replace your existing duct with hard wall duct, make sure the duct seams and joints are sealed (NOT with duct tape, lol) and the entire run is then insulated.

An alternative, if you replace that fan, consider a remote fan. Fantech is my favorite, Panasonic has good ones as well. Fantech remotes are crazy quiet, and they definitely move the air. A 6" duct can be taken down through a 4" gap with proper HVAC transition pieces. The transition piece will get smaller in one dimension and larger in the other to maintain the proper overall cross-section.

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Comments (6)

vinmarks
Original Author
8 years ago
Ok nevermind about it being a broan 70 cfm. Thats what the foremen told me. I went and checked and it is an air king 100 cfm.
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vinmarks
Original Author
8 years ago
last modified: 8 years ago
Thanks for responding Mongo. I'll try to do the best I can at answering your questions. The ceiling is vaulted. The shower is on an outside wall(right hand side in 2nd photo) and the ceiling vaults from the shower wall up to about 12 1/2 feet on the sink wall(lefthand side in 2nd photo). The existing duct work is not accessible because there is no attic above. I assume the duct is a straight run in a rafter bay but cant be positive. I'm not sure how long the run is but it cant be more then 10 feet. I've included photos of the house plans where the master bathroom is as well as the spec sheet to the fan. Not sure what you can tell from that. Bath fans can be mounted on sloped ceilings correct? My DH is going to take a look at the vent on the outside of the house tomorrow and take it off to see if we can tell what the ducting is made of. Not sure what we will even be able to tell.
Nancy in Mich
8 years ago
It seems that the venting for this fan would make a 90 degree turn really quickly in order to head back toward the shower (outside) wall. In my mind, I am seeing hot, wet air going through the fan into an uninsulated duct and hitting that 90 degree turn, and when the hot damp air hits the cold metal the water condenses and drips back out of the fan. Is the dripping worse in cool weather? Does the contractor know if the vent is insulated?
vinmarks
Original Author
8 years ago
Nancy thanks for your response. Im not sure if it is making a 90 degree turn because the unit is installed on the sloped ceiling and follows the slope. I would assume the duct runs downhill to the soffit. As far as the duct goes the formen said something about insulated ducting but he also said the fan was Broan and 70 cfm which was incorrect.

The fan does pull the steam out. We dont get any fogging on mirrors. We leave it running for at least 30 minutes afterward. The fan is already dripping before I am out of the shower. Its not a lot but several drips. We took off the vent cover at the soffit and the ducting does appear to be connected to the vent and not just laying in the soffit. We turned the fan on and there is a decent amount of air you can feel coming out.

Part of the problem is we cant access the ducting to see if its insulated and if theres turns or kinks. We hesitate to pull out the fan and even then would we be able to tell anything?

If it is due to uninsulated ducting how can it be fixed if theres no access to the ducting. Is it possible to run new ducting? Also when the term insulated ducting is used is the duct itself insulated or is separate insulation wrapped around it.

My foremen thinks its all due to the fan being on a sloped ceiling. I dont like any of his ideas as to what to do about it. I dont know what to do at this point.
Nancy in Mich
8 years ago
last modified: 8 years ago
Maybe contact Air King and ask if there is a problem with a sloped ceiling installation that could cause this? Or look online for installation instructions for sloped ceilings.