Designing Kitchens and Bathrooms - Bath Fan Exhaust Wall Cap Louvre Slats Freeze Shut

Help! We can’t use our 2 bathroom ventilation exhaust fans in the winter because the outside wall cap has 4 louver slats that freeze shut when the outside temperatures drop below 20 degrees. These wall caps exit 13 feet up on the south side of our home. Our new home (built 2005) is in Wisconsin. Once the sun heats up the south wall of our house, the slats unfreeze and the bathroom ventilation exhaust fans work beautifully.

These fans are the virtually “silent operation” QTXE Broan/Nutone models #QTXE080Fl $157 and OTXED80FL $131. To maximize sone at <0.3 and CFM performance they utilize 6” ducting. These two models are rated for bathrooms up to 75 sq. feet in size. Both of my bathrooms are under this size. The bathrooms are interior rooms with respective duct runs of approximately 15 and 24 feet.
The ducting that was used is Hart & Cooley 4.2 flexible insulated duct system.

My builder said he has never heard of this problem in his 20 years of building homes. He has always installed bath fans this way. He said they were installed according to Broans specs. He sprayed silicone spray on the wall caps slats the previous Setember. This had no effect.

My builder wanted me to use a 6" single flap wall cap but I refused because the flap would not close completely. It stayed open 3/16".

Aren't the flaps suppose to close completely so that bugs don't come in during the summer and that in the winter there aren't any back drafting of cold air??? He refuses to talk with me anymore.

It was suggested I run the fans longer. I normally run the fans for 20 minutes after I finish my shower. I did run it for six hours and the next morning the louvers froze shut again.




Why are these louver slats freezing shut and has anyone else had this problem? How did you rectify it?





Would appreciate any help you could give me.






























Thanks,

Gusmorg

To freeze shut would require, in my opinion, moisture to be available. Condensation apparently is present and it freezes when the temp dips. Is there an attic crawl that you can access and wrap the pipes with insulation? Temp variations between the outside and the vent are causing the condesation to form.

Is the vent caulked or sealed in anyway to prevent airleaks around it?

If access is limited, can you pull the louver cover off from the outside and stuff some insulation in? then caulk it

Anyone else have any thoughts to help Gusmorg out?

Use a direct turndown screened exhaust for a dryer. There is a flap, but it is not exposed to the outside weather, and should free itself up once warm air hits it.

PROBLEM: Bathroom exhaust fans. Outside vent wall caps are 4” in sizing and have 4 plastic louvers that freeze shut when outside temperatures drop below 20 degrees. Our home is in Wisconsin and was built in 2005. These vent caps are on the south side of the house and once the sun heats up the south wall, the ice melts and the bathroom fans can then be run. Fans work perfectly during all other times of the years. After taking a shower we run the fans for 30 minutes.

Further details:

Inside humidity: Winter 30-40%
Summer 38-52%
We have run humidity tests in the bathroom. Before a shower humidity reading was 38%. After taking a shower for 5 minutes the humidity reading was 51%. Within the next 6 minutes the humidity reading dropped to back down to 38%. Note: The lowest humidity reading in our home has been 31% and these vents still froze up.

Bathroom Dimensions: 75 sq. feet
63 sq. feet
These bathroom do not have outside walls and have no windows in them.


Fan Specs: Bathroom #1 Broan/Nutone QTXE080FL (with a light) $157
Bathroom #2 Broan/Nutone QTXED080FL $131
CFM 80, Sone 0.4 on both fans
These fans have nearly silent operation and the motor was engineered for continuous operation.

Duct Specs & Run Length: Hart & Cooley 4.2. – 6 inch sized, as per manufacture’s instructions This duct work comes entirely factory insulated. In addition our attic has additional blown-in insulation to R38. This insulation was blown over the top of the Hart & Cooley insulated duct runs. The duct runs are approximately 15 ft and 24 ft long to the outside vent wall caps.

The builder says in 20 years of building homes he has never had this problem. The Broan/Nutone tell us they have never heard of this problem. The Energy Star people we spoke with said everything sounds like it has been installed correctly. Has anyone had this same problem and how did you fix it?

I would try WD-40 on the flap. After all its generic title is "Water Displacement formula #40". Everyone poo poos the use of it, but it works for a variety of things, including water displacement, which you need.