Why does my bathroom fan not remove moisture properly?

Your bathroom fan likely isn't removing moisture effectively due to inadequate airflow capacity, poor installation, or blocked ventilation pathways. Most moisture problems stem from undersized fans, improper ducting, or fans that aren't running long enough after showers.

Fan Sizing and Performance Issues

The most common culprit is an undersized fan. Your bathroom fan should move at least 1 CFM (cubic feet per minute) per square foot of bathroom space, with a minimum of 50 CFM for bathrooms under 50 square feet. Many Toronto homes, especially older ones, have builder-grade fans rated at only 50-70 CFM that simply can't handle larger bathrooms or heavy moisture loads. For bathrooms over 100 square feet, you'll need fans rated at 100+ CFM.

Fan age also matters significantly. Fans over 10-15 years old lose efficiency as motors wear down and blades accumulate dust and debris. If your fan sounds louder than a quiet conversation (over 3 sones), it's likely struggling and needs replacement.

Ducting and Installation Problems

Poor ducting is extremely common in Toronto's older housing stock. Many bathroom fans are incorrectly vented into attics, soffits, or even back into the house rather than directly outside. This creates moisture problems in your attic and doesn't actually remove humidity from your home. Proper installation requires ducting that runs directly to an exterior wall or roof vent with minimal bends and smooth, rigid ducting rather than flexible corrugated pipe.

Duct length and diameter also affect performance. Long duct runs (over 25 feet) or multiple bends can reduce airflow by 50% or more. In Toronto's climate, uninsulated ducts in cold attics cause condensation that drips back into the fan housing, reducing efficiency and potentially causing water damage.

Usage and Maintenance Factors

Many homeowners don't run their fans long enough. The fan should operate during showers and for at least 20-30 minutes afterward to remove residual moisture. Consider upgrading to a fan with a humidity sensor or timer switch that automatically runs the fan for the appropriate duration.

Regular maintenance is crucial but often overlooked. Dust buildup on fan blades and grilles can reduce airflow by 30-40%. Clean your fan housing and grilles every 6 months, and replace the fan motor if it's making excessive noise.

Toronto-Specific Considerations

Ontario Building Code requires bathroom fans to exhaust directly outside, not into attics or crawl spaces. In Toronto's freeze-thaw climate, improper venting can cause ice dams and moisture damage. Many century homes and older Toronto properties have inadequate bathroom ventilation that doesn't meet current standards.

When to Call a Professional

Electrical work for fan installation requires ESA permits in Ontario. If you're experiencing persistent moisture problems, mold growth, or need to run new ducting, hire a licensed contractor. Improper electrical work or inadequate ventilation can create safety hazards and void insurance coverage.

Next Steps

First, measure your bathroom and check your current fan's CFM rating (usually printed on the housing). Clean the fan thoroughly and ensure you're running it long enough. If problems persist, have a contractor assess your ducting and recommend a properly sized replacement fan with direct exterior venting.