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OBC DIVISION B · PART 9 · SECTION 9.22 — FIREPLACES

What clearances and damper requirements apply to fireplaces in Ontario?

Combustible trim and mantels must keep prescribed distances from the fireplace opening, on the order of 150 mm (6 in.) for flush trim and more for projecting shelves. Every fireplace needs a damper that can close off the throat or flue, and site-built fireplaces need combustion air provisions.

Code reference
The fireplace provisions require minimum clearances between the fire chamber opening and combustible materials, with greater clearances for elements that project from the wall face such as mantel shelves. A damper sized to substantially close the flue passage is required, and fireplaces must have provisions such as outdoor combustion air and tight-fitting doors to limit uncontrolled air loss.
OBC Division B, Section 9.22.

Paraphrased for clarity — open this provision in the BUILDAiD Library for the exact wording.

What this means in practice

The pattern to remember is that the closer and more projecting the combustible element, the larger the clearance: flush tile-to-wood joints near the opening are the usual violation, followed by chunky wood mantels installed too low. Dampers matter for both safety and energy, since an open flue is a running hole in the building envelope; glass doors and exterior combustion air ducts address the same problem. Factory-built fireplaces override these site-built rules with their listed installation instructions, which become the code requirement for that unit, so keep the manual for inspection.

Plain language

Wood trim needs breathing room around a fireplace opening, roughly 150 mm for flat trim and more for a shelf-style mantel that sticks out. And every fireplace needs a working damper, a metal flap that shuts the chimney when you are not burning so your heated air does not escape.

Related questions

How big does a fireplace hearth extension need to be in Ontario?

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This page is provided for general information. Building code requirements depend on your specific project, occupancy and municipality, and code editions change. Always verify requirements against the current Ontario Building Code and confirm with your local building department.