How often should I run my bathroom fan in Vancouver to prevent condensation and mould growth?

In Metro Vancouver's humid climate, your bathroom exhaust fan should run during every shower or bath and for a minimum of 20-30 minutes afterward — and ideally, you should consider running it on continuous low speed (20-30 CFM) around the clock if your fan supports that mode. Unlike drier regions of Canada where a quick post-shower fan cycle is sufficient, Vancouver's persistent outdoor humidity of 75-85% means moisture does not dissipate on its own, and bathrooms that are not actively ventilated can remain dangerously humid for hours.

The most common mould-causing mistake in Vancouver bathrooms is turning the fan off too soon — or not turning it on at all. A typical shower generates 2-3 litres of water vapour, and in Metro Vancouver's marine climate, that moisture has nowhere to go without mechanical ventilation. Opening a window is not a substitute — the outdoor air is already carrying significant moisture, especially from October through April when rainfall averages 150-200 millimetres per month.

For daily use, follow this protocol. Turn the fan on before you start the shower (this creates negative pressure that draws steam toward the exhaust rather than letting it spread to other rooms). Leave the fan running for at least 20 minutes after you finish showering — 30 minutes is better. If multiple family members shower in sequence, keep the fan running continuously throughout and for 30 minutes after the last shower. For baths, the same 20-30 minute post-use run time applies.

The best solution is to eliminate the need to remember. A humidity-sensing switch (also called a humidistat switch, $50-$120 at Metro Vancouver plumbing and electrical suppliers) automatically turns the fan on when relative humidity in the bathroom rises above a preset threshold — typically 60-65% — and turns it off when humidity drops to an acceptable level. This removes the human factor entirely. A timer switch ($30-$60) is a simpler alternative — you press a button and the fan runs for a set period (20, 40, or 60 minutes) before shutting off automatically.

For homes with chronic moisture issues — common in older Vancouver neighbourhoods like Kitsilano, Main Street, East Van, and the North Shore — consider a fan with a continuous ventilation mode. Fans like the Panasonic WhisperGreen Select ($200-$400) run continuously at a whisper-quiet 20-30 CFM (0.3 sones — essentially silent) to provide constant background moisture removal, then automatically boost to 80-110 CFM when the humidity sensor detects shower moisture. This continuous approach is the gold standard for Vancouver bathrooms and costs roughly $1-$3 per month in electricity.

Specific scenarios for Metro Vancouver homeowners:

In condo and strata bathrooms with centralized exhaust systems, your fan may already run continuously at low speed as part of the building's mechanical ventilation design. Check with your strata management to understand how your building's system works before making any modifications — strata bylaws typically require approval for changes to mechanical systems.

In basement suite bathrooms — extremely common in Metro Vancouver's housing stock — ventilation is even more critical because below-grade spaces are naturally cooler and more prone to condensation. Run the fan longer (30-45 minutes post-shower) and ensure the exhaust duct runs to the exterior, not into the crawlspace or main floor.

In bathrooms without windows (common in interior bathrooms and many condos), the exhaust fan is your only moisture removal system. Consider running it on a continuous low setting or installing a humidity-sensing switch that keeps it running whenever relative humidity exceeds 60%.

Signs your current fan usage is inadequate include condensation on mirrors and windows that persists more than 15 minutes after showering, musty odours, mould spots on caulking or grout, peeling paint on the ceiling, and moisture stains on walls. If you notice any of these in your Vancouver bathroom, increase your fan run time, check that the fan is actually exhausting air (hold a tissue near the grille — it should be drawn toward the fan), and verify the duct terminates at the exterior.

All electrical work related to fan switches, including installing humidity-sensing or timer switches, must be performed by a licensed electrician per BC code, with inspection through Technical Safety BC. Installation of a new switch typically costs $150-$300 including parts and labour.