Should I close my fireplace damper during Ottawa's humid summer months or leave it partially open for airflow?

Leaving your fireplace damper closed during summer is the right move — this protects your home's conditioned air from escaping up the chimney and keeps humid outside air from entering through the flue. A closed damper acts as a seal between your living space and the outdoors, which matters significantly in Ottawa's hot, humid summers when your air conditioning is working hard.

Why This Matters in Ottawa's Climate

Ottawa summers are notoriously sticky, with humidity levels regularly climbing above 70 percent and temperatures hitting +30 to +35 degrees Celsius. Every time cool air leaks out of your house through an open damper — even a partially open one — your AC system has to work harder to replace it. Over the course of a three-month summer, this inefficiency adds up on your hydro bill. More importantly, an open damper creates a direct pathway for humid outdoor air to enter your home, potentially drawn down the chimney by pressure differences and air conditioning operation. This moisture can condense on chimney interior surfaces and the damper itself, creating ideal conditions for mold growth inside the flue.

The other consideration is pests and wildlife. An open damper during summer is an invitation for birds, squirrels, insects, and bats to explore your chimney system. Ottawa's wildlife quickly figures out that a dark, cool chimney is attractive real estate during hot months — and discovering a bird's nest or bat droppings when you fire up your fireplace in fall is neither pleasant nor hygienic.

How to Properly Close Your Damper

If you have a traditional masonry fireplace, close the damper fully by turning the handle or lever until you feel resistance — do not force it, as dampers can jam or break. Check that it seats tightly by holding a lit candle or incense stick near the damper opening; the smoke should not be pulled upward if the seal is good. Many older damper mechanisms wear out over decades and no longer seal completely, which means you may have air leakage even with the damper "closed." If you notice cold air or moisture issues during summer, your damper may need replacement.

For gas fireplaces with a sealed combustion chamber (direct-vent units), damper position is not relevant — the appliance draws air from outside through a dedicated intake pipe, so the chimney damper does not affect operation. The flue should be fully closed when the fireplace is not in use.

For wood stoves, there is no damper in the traditional sense — these appliances have a draft control or air inlet that regulates oxygen to the fire. Keep this fully closed during summer when the stove is not in use to prevent reverse draft and chimney odours.

Additional Summer Fireplace Maintenance

While your fireplace is closed up for summer, this is actually an excellent time for a WETT Level 1 inspection (around $250 to $450 in Ottawa) to check for any damage that occurred during the heating season — spalling brick, deteriorated mortar joints, or creosote buildup. Summer is also when you should have your chimney professionally cleaned before fall arrives, rather than waiting until October when every sweep in Ottawa is booked solid. Scheduling your chimney sweep and inspection in June or July means you will be ready for the first crisp September nights when people suddenly want their fireplaces again.

If you are uncertain whether your damper is sealing properly or suspect moisture issues in your chimney, a WETT-certified chimney professional can assess the situation and recommend repairs — you can browse fireplace contractors through the Ottawa Construction Network directory if you need to connect with a local chimney sweep or inspector.

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Looking for experienced contractors? The Ottawa Construction Network connects Ottawa homeowners with qualified professionals:

• Apple HVAC and mechanical
• RenoMotion Inc.
• Joe Imerti Contracting
• Denys Builds Designs Renovations
• Leeds Property Maintenance