Proper ventilation is very important

Hey there, time traveller!
This article was published 20/01/2002 (8865 days ago), so information in it may no longer be current.

Today’s question deals with a topic that I have received many inquiries about, and have recently addressed. I feel that the issue of bathroom ventilation is very important to understand and will try to minimize the confusion about this much-needed system.

Question — I have two bathrooms without exhaust fans.

The upstairs bathroom is beside a closet, which has a copper plumbing stack running through it that is approximately 2″ in diameter. If I put a new exhaust fan in the bathroom wall near the ceiling and exhaust it into the stack pipe, I can easily run electrical to the fan. The house is a bungalow, and I can get electrical into the attic, although this would be more difficult and the fan switch would end up in a less desirable location. I’d also expect to have more issues with insulating around the fan housing and exhaust pipe if I go through the attic.

Is exhausting a fan into a plumbing stack pipe acceptable? Could odours come through the bathroom fan if the stack is for a toilet, or even just for sinks or a washing machine? I’d also prefer not to vent though the roof. If I can’t vent through the plumbing stack and I put the fan in the ceiling, can I run the vent out through the soffits?

The basement bathroom also has no exhaust fan, and has a finished ceiling. The previous owner installed a fan, but vented it into the cavity under the upstairs bathtub. I haven’t used the fan, except to check that it works. I can’t imagine this is a good place to vent the humid air from the bathroom. I can easily run the exhaust from this fan to the clothes dryer vent pipe. Is this acceptable?

If I have to tear open the drywall ceiling, drill through the foundation wall, and rip open walls to find the wiring, I’d probably not bother.

Any alternatives you could offer would be appreciated.

–Rob Derksen e-mail

Answer — I applaud Mr. Derksen for attempting to find a way to add exhaust fans to his two bathrooms, but do not agree that he should give up his efforts if it becomes too difficult. Proper bathroom ventilation and exhaust fans are critical for getting rid of excess humidity produced by washing, bathing and showering that can cause severe moisture damage to components in the home. Spending a little money on a properly installed fan now may save very costly repairs in the future. Lack of ventilation can also lead to a buildup of mould, which may be harmful to family members with high sensitivity, allergies, or breathing problems. Good ventilation will also quickly remove annoying waste odours from bathrooms.

The answer to Mr. Derksen’s first question is a resounding NO! Odours from the vent pipe and noxious sewer gas could easily escape the vent pipe if attached to the exhaust fan, and come back into the house. This would also be improper because bathroom exhaust fans normally require a minimum 3″ diameter pipe for ventilation and many use a 4″ duct. Mounting the fan in the ceiling is not that difficult, if the access hatch to the attic is not too far away. The fan can be properly insulated and vapour barriered and an insulated duct can be easily attached to a roof or gable end mounted vent hood. I would not recommend installing the vent termination under a soffit, as the moisture can cause peeling paint and rot in the wood of the soffit area.

As far as the basement bathroom goes, Mr. Derksen is very wise not to run the current fan with the duct emptying below the upstairs bathtub. This would cause a huge amount of moisture under the tub that would quickly rot wooden components in this area.

Tying in the bathroom pipe with the existing dryer vent is not recommended and would require major modification of the piping and the exit hole through the foundation wall. If extending the fan duct to this location is easy, as suggested, an additional hole through the foundation wall is a minor issue. Drilling a 3″ or 4″ hole through the concrete is a simple procedure and can normally be done for under $100. A contractor with a diamond hole saw will drill the hole in about an hour, from the exterior of the house, which will minimize the mess. Once the hole is drilled, it is very easy to install a vent hood and connect it to the duct from the fan. Care should be taken to locate the hood in a spot that has good airflow, will not be covered by snow or vegetation.

Ari Marantz is owner/inspector of Trained Eye Home Inspection and is the P. R. Rep. for the Canadian Association of Home Inspectors- Manitoba (www.cahi.mb.ca). Questions can be e-mailed or sent to: Ask The Inspector, P. O. Box 69021, #110-2025 Corydon Ave., Winnipeg, MB. R3P 2G9. Ari can be reached at (204) 291-5358.

trainedeye@iname.com