Do I need to remove or seal my existing damper before installing a fireplace insert in Ontario?

Yes, you almost always need to remove or permanently seal your existing damper before installing a fireplace insert — this is a critical safety requirement under the Ontario Building Code and WETT standards, and it's one of the most commonly overlooked steps in fireplace insert installation.

Here's why this matters so much in Ottawa's climate: when you install an insert into an existing masonry fireplace, the insert becomes the primary heating appliance and has its own chimney pipe that vents through the existing chimney flue. The original damper — which was designed to seal the open fireplace when it wasn't in use — now sits above the insert pipe. If the damper is left in place and accidentally closed, combustion gases (including deadly carbon monoxide) from the insert get trapped inside your home instead of venting up the chimney. This creates an immediate and serious carbon monoxide poisoning hazard. Even if the damper is left in the open position, a loose, deteriorating, or corroded damper can drop metal debris or soot into the insert pipe, clogging the vent and creating dangerous back-drafting conditions. The damper also becomes a barrier to proper chimney draft — the insert pipe needs direct, unobstructed access to the full chimney flue above it.

The correct approach is to permanently remove the damper assembly entirely or seal it shut with mortar so it cannot be operated. Most fireplace professionals remove the damper completely — this involves unbolting the cast iron damper frame from the fireplace throat, removing the damper blade, and extracting the hardware. If the damper is structurally integrated or difficult to remove, it should be sealed solid with refractory mortar or concrete to prevent it from ever being closed again. Some installers place a permanent warning label or mark on the fireplace to indicate the damper is sealed. This prevents future homeowners or contractors from accidentally closing it and creating a carbon monoxide trap.

A few critical considerations: first, if you're having a professional install your insert (which you should be — insert installation requires WETT certification and typically involves structural work at height inside the fireplace), the contractor will handle damper removal as part of the scope of work. Ask the installer explicitly to confirm in the written quote that damper removal or sealing is included and that they will dispose of the damper properly. Second, do not attempt to operate or close your fireplace's damper after an insert is installed — if you are unsure whether your damper has been removed or sealed, contact your WETT inspector or the original installer immediately. Third, after damper removal or sealing, you'll need a WETT Level 2 inspection to confirm the entire system is safe and compliant before you use the insert. This inspection typically costs $350 to $600 in Ottawa and is non-negotiable if you want insurance coverage for your new appliance.

The bottom line: damper removal is not an optional step or a cost-saving measure you can skip. It's a fundamental safety requirement that protects you from carbon monoxide poisoning. If a contractor quotes you an insert installation without explicitly including damper removal, that's a red flag — ask why, and get clarification in writing.

When you're ready to move forward with an insert installation, you can browse WETT-certified fireplace installers and chimney professionals through the Ottawa Construction Network directory at justynrookcontracting.com/directory to find experienced contractors in your area who understand Ontario's safety requirements.

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

• 613Bins
• RenoMotion Inc.
• Joe Imerti Contracting
• Valcor Construction
• Capital City Drywall