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Hello, I have to connect the ventilation of the exhaust fans of my 3 upstairs bathrooms to the outside and I am getting conflicting advise from 3 different contractors. The issue is that I have no siding in the attic, so the options are either connect the exhaust fans to the soffit or to connect them to the roof (and getting ourselves into roofing territory in PA, where it snows and it gets very cold in the winter). Here is the explanation of each contractor:
- Bathroom remodeling contractor: He says that it should go to the soffit because if it goes to the roof and it's cold outside, when the moisture hits the roof it will become ice right away and the ice will get in between the shingles and it will damage my roof. I looked up the code, which states that it cannot go to the soffit... to which the bathroom contractor replied that his intention is not to go to the soffit but into the soffit. He is also the one that messed up and left the exhaust fans to ventilate into my attic. He doesn't have insurance to touch my roof and it seems that he doesn't want to take responsibility for his mistake.
- Electrician: He says that the tube will be only 3 feet long and the condensation will not be enough to be of any problem.
- Mold Remediation Contractor: He says there is a reason why current building code requires “positive ventilation” to the exterior for bathroom fans and dryer vents. Venting to the soffit creates an additional problem in that as air moves through the attic it travels from the soffit to the ridge which puts pressure on the vent fan that it cannot overcome. The air from the vent fan will tend to return to the attic concentrating moisture in one area.
Please give me your expert opinions!!! Thank you!!!!
 

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retired framer
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In our code if we have a common soffet where the air can travel side ways we can install 6 ft of unvented soffet and have the exhaust in the middle of that. I have watched what happens when the neighbour took a shower and that 6 ft is not enough the steam followed along the soffet for 10 ft with just a little breeze.
The ice dam is a limited problem on the roof because water can run sideways around the dam which is much different than an ice dam over the exterior wall.

What do the city inspectors say about this?
 

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Bath exhaust fans should also have a "delayed off" timer to keep the fan running about 20 minutes after the shower and light are turned off. That additional run time will also purge the duct and vent hood of excess moisture.

Although I prefer through the roof venting this vent hood is designed to exhaust the air down and away from the soffit area.

Bud
 
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Hammered Thumb
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I looked up the code, which states that it cannot go to the soffit
Which code, because you cannot just run a pipe to the soffit (or roof vent) and let it exhaust from the attic through the soffit perforations (or ridge or box vent). But you can have a pipe with its own termination cap through the soffit (or roof).
 

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Usually Confused
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Interesting that I had this type of discussion with my HVAC repair guy yesterday when he happened to mention they also install power vents. We are in a high snow load area. They prefer not to go through the roof for liability reasons, both potential roof damage and workers going on the roof. A reasonable length attic run of ducting can be insulated. A friend thought he would solve this by extending the abs vent above the typical snow line - it froze.

We currently have a recirculating stove hood, but when the time comes, I will consider a soffit vent. The problem of exhaust air recirculating back in through the soffit as Neal mentions would be a concern, but I think several feet of non-vented soffit would solve the problem. We have the vent capacity to sacrifice, other homes may not.
 
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