During my more than 15 years inspecting homes, I have seen many issues caused by bathroom exhaust fans and ducting. A lot of time the issues can cause high humidity, condensation, mold, and structural roof damage, all potential health concerns and possible major repair costs. I have seen these issues over and over when most can be repaired and avoided. These fans are called “supplemental exhaust” in OBC 126.96.36.199 according to the Ontario and Canadian Building codes. They provide additional ventilation to a high humidity area of a home. According to the Building Code a bathroom is required to have either natural ventilation (a window that opens) or mechanical ventilation (an exhaust fan) for ventilation. The five most common issues with bathroom exhaust fans you should know and look for are: The fan is noisy! If the fan is used every day, in time it will wear out (the motor or bearings) and begin making noise upon start up or continuously during operation. It’s time for replacement. This can usually be done without damage to ceiling by just swapping out the old fan and motor while on a ladder in the room. Be sure to follow the manufacturer’s installation instructions and turn off electrical power to the fan. The fan does not suck! By this I mean it does not suck much air at all. How do you know? A quick test all inspectors use is to take one piece of toilet paper and place it against the fan grill on the ceiling. If the fan can’t suck enough air to hold it then it SUCKS and there is a problem! Either the fan is old and it needs to be replaced or the exhaust is blocked. Sometimes I’ve seen a fan wired backwards and its blowing air instead of sucking. Usually if the fan is old, making more noise than normal, and it is not sucking, more than likely it just needs to be replaced. The duct going through the cold attic is not insulated. According to OBC 188.8.131.52 (3) the duct must be insulated. The reason for this is to help stop condensation. It’s a cold -20C winter day and you are having a shower, the warm moist air rises quickly to the ceiling in the bathroom and the fan is pulling this air into the flexible ducting. The attic temperature is close to the outside temperate and definitely cold. The warm moist air meets the cold surface of the inside of the duct and instantly causes condensation. This is bad. The moisture could run back to the fan and leak on to the drywall ceiling or leak on to the insulation both probably causing mould...
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