Ventilation near you

Spot ventilation removes moisture and pollutants right where they are produced, when they are produced. Whole-house ventilation supplies a steady flow of fresh air to the entire home. Most houses need both.

Health Canada's mould guide says to use an exhaust fan when you shower or bathe, and to check that fans move enough air and are vented to the outside, not into the attic. It also advises always using the range hood when cooking, preferably on the highest setting. Natural Resources Canada adds that every fan should exhaust fully to the exterior, with air sealing built into the installation, and recommends avoiding range hoods that recirculate air back into the room.

The attic rule matters because an attic is cold in winter. Warm, humid bathroom air dumped there condenses in the insulation and on the underside of the roof sheathing, leading to frost, stains, mould and rot. The same thing happens when a duct slips off its fitting, sags or stops short of the roof or wall cap.

Air that a fan pushes out has to be replaced from somewhere. Natural Resources Canada explains that when less air is supplied to a house than is exhausted, negative pressure builds up and can produce backdrafts of combustion gases. Its air-leakage guide makes the same point from the other side: as a house gets tighter, less air is available for combustion appliances, and without enough air a chimney or flue can spill dangerous gases into the house.

The risk rises when a high-capacity range hood, a clothes dryer and bathroom fans run at the same time in a tight house, especially one with a naturally drafting furnace, boiler, water heater or fireplace. The fix is designed by a qualified HVAC or gas technician: sometimes a dedicated makeup air supply that opens when the hood runs, sometimes a change of appliance. Never adjust gas appliances or their venting yourself.

Natural Resources Canada observes that noisy fans tend not to be used much because they are annoying. It recommends ENERGY STAR certified fans and says quieter models designed for continuous use are worth buying. It also suggests a simple timer or humidity controller that turns the bathroom fan on or off automatically, so the room gets proper ventilation without being over-ventilated. Fan boxes list a loudness rating; the lower it is, the quieter the fan.

Building codes set out how houses must be ventilated, and each province adopts and amends its own code, so the details depend on where you live and when the house was built or renovated. In general, newer homes are designed with mechanical ventilation and with exhaust in bathrooms and kitchens, while older houses often relied on leaks and opening windows.

Ask your municipality whether your project needs a permit, particularly a new bathroom, a basement suite or a major renovation, and expect the inspector to look at exhaust fans and where their ducts end. Fans and controls are wired by a licensed electrician, and any change to how a gas appliance vents or gets its combustion air is handled by a licensed gas technician.

Natural Resources Canada's air-leakage guide warns that as the building envelope is tightened, household humidity rises and can create condensation and moisture problems. That's no reason to skip air sealing; it's a reason to plan ventilation alongside it. Our air sealing page covers the envelope side of the job.

Fans lose airflow gradually as dust and lint build up, and a stuck damper or blocked hood can stop them almost completely. A quick check each season keeps them working.