Do I need a makeup air kit for my gas fireplace if I also run a big range hood in my Ottawa home?

The short answer is: it depends on your home's tightness and your gas fireplace type, but in Ottawa's climate, a makeup air kit is a smart precaution if you run a powerful range hood and have a direct-vent gas fireplace — and it's essential if you have a B-vent unit.

Here's why this matters specifically in Ottawa. Modern Ottawa homes, especially those built in the last 15 to 20 years, are increasingly well-sealed for energy efficiency. This is great for keeping heating costs down during our brutal winters, but it creates an indoor air pressure problem that earlier, leakier homes never had to worry about. A powerful range hood — the kind rated at 400 CFM or higher that's common in updated kitchens — can create negative pressure in your home by pulling a large volume of air out of the house. If your gas fireplace is a direct-vent unit (which draws combustion air from outside through a sealed pipe and exhausts through a separate sealed pipe), negative pressure is less of a concern because the fireplace isn't competing with the hood for indoor air. But if you have a B-vent gas fireplace (which draws combustion air from inside your home), a powerful range hood running simultaneously can create what's called backdrafting — the negative pressure forces combustion gases, including carbon monoxide, back into your living space instead of up the vent pipe.

A makeup air kit is a dampered duct that brings fresh outside air into your home to replace the air the range hood exhausts, equalizing pressure and preventing backdrafting. In Ottawa, makeup air kits typically cost $300 to $800 installed, depending on whether the ductwork requires routing through finished spaces or can run through existing cavities. The kit includes an outdoor damper hood (to prevent cold winter air from flowing backward when the range hood is off), internal damper, and ducting back to the kitchen or main living area. Many setup integrate the makeup air inlet into the return air system of an existing HVAC system, which also filters and conditions the incoming air — a practical advantage during Ottawa winters when bringing in raw -25 degree air is uncomfortable without tempering.

If you have a direct-vent gas fireplace, you may not absolutely need a makeup air kit, but it's still worth considering if your range hood is very powerful (500+ CFM) or if you plan to run the hood frequently while the fireplace is operating. The extra cost of a makeup air kit is cheap insurance against creating negative pressure problems. If you have a B-vent gas fireplace, a makeup air kit is highly advisable — running a powerful hood without makeup air essentially creates a vacuum that can pull dangerous combustion gases back into your home.

One important note: if your gas fireplace is B-vent and you already have an installed system without makeup air, avoid running the range hood while the fireplace is in use. This is a genuine carbon monoxide risk, not an inconvenience. A carbon monoxide detector should absolutely be installed on the same level as your gas fireplace, and ideally near bedrooms — if the detector ever alarms while the fireplace is running, stop using the fireplace immediately and have it professionally inspected by a TSSA-licensed gas fitter.

If you're planning a gas fireplace installation or considering whether your current setup is creating pressure imbalances, a fireplace professional can assess your home's air tightness, range hood CFM rating, and current fireplace venting to recommend whether makeup air is necessary. You can browse experienced gas fireplace installers through the Ottawa Construction Network directory if you'd like professional guidance on this specific issue.

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