Is it normal for my bathroom mirror to fog up and stay foggy for over an hour after a shower, or is that a ventilation problem?

Yes, that's a ventilation problem — a mirror that stays fogged for over an hour after a shower is a clear sign your bathroom exhaust fan is undersized, underperforming, or both.

A properly ventilated bathroom should clear mirror fog within 15 to 20 minutes of the shower ending. When moisture lingers for an hour or more, it means humid air is sitting in the bathroom rather than being exhausted to the exterior. That chronic moisture exposure is doing damage you can't see — inside your walls, above your ceiling, and behind your tile.

What's likely causing it

The most common culprit in GTA homes is an exhaust fan that was never properly sized for the bathroom. Ontario Building Code requires mechanical ventilation in every bathroom, with a minimum of 50 CFM for a standard bathroom — but that 50 CFM minimum is exactly that, a minimum. For a typical 5x8-foot bathroom (the most common layout in post-war Toronto bungalows and inner-suburb homes), you want at least 80 CFM. For a bathroom with a soaker tub, steam shower, or any space larger than 100 square feet, 110 CFM or higher is appropriate.

The second common cause is a fan that's venting into the attic or soffit instead of directly to the exterior. This is unfortunately common in older Toronto homes and even some 1980s-1990s suburban builds across Mississauga, Brampton, and Markham. The fan sounds like it's working, but the moist air is just dumping into your attic — which creates mould conditions up there while doing nothing for your bathroom. A proper exhaust installation runs insulated duct from the fan to a dedicated exterior wall cap or roof cap.

The third possibility is a fan that's simply worn out. Bathroom fans accumulate lint and dust on the grille and impeller blades, which dramatically reduces airflow over time. A fan that moved 80 CFM when it was new might be moving 30 CFM after a decade of use without cleaning.

GTA-specific context worth knowing

Toronto's combination of hot humid summers and cold winters makes this more than a comfort issue. In summer, bathroom moisture compounds the already-high ambient humidity that lakefront and downtown neighbourhoods experience. In winter, that moisture-laden air hitting cold exterior walls and window frames creates condensation that leads to paint peeling, drywall softening, and eventually mould growth inside wall cavities. The freeze-thaw cycles GTA homes experience 40-60 times per year make any moisture intrusion into wall assemblies particularly damaging.

In condos, the situation has an added wrinkle — your exhaust fan connects to building-provided ductwork with a specific damper and connection point. If that damper is stuck or the shared exhaust system is restricted, even a properly sized fan won't perform well. This is worth raising with your building management.

Practical steps to diagnose and fix it

Start by cleaning your fan grille and impeller — remove the cover, vacuum out the dust, and wipe down the blades. Then do the tissue test: hold a single sheet of tissue up to the fan grille while it's running. It should be pulled firmly against the grille and held there. If it flutters or falls, your fan isn't moving enough air.

Check where your duct exits the building. Go into your attic (if accessible) or look for an exterior wall cap or roof cap. If you can't find one, or if the duct terminates in the attic, that's your problem.

If the fan is more than 10 years old, undersized, or venting improperly, replacement is the right answer. A quality bathroom exhaust fan from Panasonic or Broan in the 80-110 CFM range runs $80-$200 for the unit. Installation by a licensed electrician — including proper exterior-vented ductwork — typically runs $300-$600 in the GTA depending on duct routing complexity.

When to call a professional

Cleaning the fan is a reasonable DIY task. But if the duct needs to be rerouted to the exterior, or if a new circuit or wiring is required for a replacement fan, that work requires a licensed electrician and an electrical permit in Ontario. ESA inspection is required before the work is concealed. Don't skip the permit — it protects you and ensures the installation is safe.

If you've had persistent fogging for years and notice any soft drywall near the shower, peeling paint on the ceiling, or discolouration around the fan grille, it's worth having a contractor assess whether moisture damage has already occurred inside the wall or ceiling assembly. That's not a cosmetic issue.

Need help finding a bathroom renovation professional to assess your ventilation situation? Toronto Bath Remodeling can match you with a local contractor for free — or browse professionals through the Toronto Construction Network directory at torontoconstructionnetwork.com.