What sucks in, must blow out!

WHEN you turn on that bathroom  fan, you want to get rid of odours FAST. If the fan sounds loud and the smell dissipates – end of story – right? But do you check the other end of the pipe? During my home inspections in the Toronto area, I try to at least verify that suction is effective, and FIND the other end of the pipe.

bathroom fan grill - dirty
One really important function of fans is to push stale and moist air from inside to out. The exhaust end must vent all the way to the outside of the house, and be dedicated to one duct only. Here’s some cases when it doesn’t and why that’s a bad thing;

    • Venting into attic, ceiling or wall space – puts moist air into a confined space which can cause mold and deteriorate roof structure. Sometimes you can see the duct ends inside the attic. A clue to a problem, even if you can’t see a duct venting in here, is lots of spider webs. A dry, well vented attic actually has very few spider webs visible. Moisture attracts bugs, and in turn other critters.
    • Connected to plumbing waste stack vent – an unprofessional shortcut. The waste vent carries sewer gasses, and these can backdraft into your fan ducting, causing smells, corrosion/leaking and possibly electrical/fire hazard.
    • Connected to another fan duct – laundry or kitchen. Again, not good – air can go back down into the other room in the right conditions.

The fan duct may terminate on the roof, through the soffit (not ideal) or through the wall. The ideal configuration depends on the location and type of house structure.

The first step a homeowner can do to see how their stuff works is to check the fan’s suction by putting a piece of paper against the grill in the ceiling while the fan is on. The air suction should be able to at least hold the paper against the grill by itself. Now close the bathroom door and window – is the fan pulling air under the door into the room? This is how it should be. If you can’t detect a strong airflow with these methods, it’s not working right.

The second step is to locate the exhaust on the outside of the house. You should be able to match each fan, if more than one, with each exhaust port. duct terminus

Make sure the inside grill and exterior exhaust hood are clean and free of debris or blockages. Look inside from both ends.

Sometimes on a really cold day, if you are venting from a warm humid bathroom, you will see the vapour coming out the exhaust. If the discharge point is reachable from the ground, you may be able to feel the airflow with your hand. For higher vents, you can check from a ladder.

If you have a clear intake and exhaust but you are not getting good airflow from inside to outside, there could be problems with the ducting between them (too long, kinked, blocked, open joints).

If you can tell air is being sucked from the inside but you can’t tell where it is going, there are various devices for generating a visible smoke for visual testing. Test matches, puffer sticks, smoke candles, smoke bottles, etc.

A little bit of investigation of your fans can go along way to preventing major damage in your house. If it’s not working right, have it professionally fixed – and check it after it’s been done.