Somebody wants a 600 CFM range hood over a gas range. Beautiful kitchen. Then the designer asks where the replacement air is coming from, and the room goes quiet.
In a tight house every cubic foot the hood blows outside has to come back in from somewhere. Plan where, or the house will pick for you, and it might pick the chimney. Here is what the 2024 code changed and how to handle it.
A range hood pushes air outside. In an old drafty house, replacement air leaked back in through a hundred cracks. In a tight new house, or an old one after new windows and spray foam, there are no cracks.
So the house goes negative. Air gets pulled in wherever it can: around doors, through the dryer vent, down a fireplace chimney, or back down the vent of a gas water heater. That last one brings combustion gases with it.
The 2024 Ontario Building Code added prescriptive requirements for makeup air, Article 9.32.3.8 according to the Ontario Building Officials Association. Check your hood against it before you buy, not after the inspector asks.
An outside air duct with a damper that opens when the hood runs. The most common answer.
The incoming air is warmed so the kitchen is not hit with -20 C air in January. Part of the heat load.
The makeup air has to match what the hood actually exhausts. Bigger hood, bigger opening.
Sometimes the best fix. A well-designed hood that captures well can do the job with less airflow.
Every load pushes a lot of air outside.
Small each, but they add up.
If it vents outside, it exhausts too.
They need combustion air and must not be fighting the hood. See wood stoves and tight houses.
Your ventilation design should look at all of them together. That design goes on the ventilation summary (RMVDS) for your permit.
Tell your designer the hood size before the HVAC design is done. The makeup air system, its duct, its damper and any tempering go on the drawings with the rest of the ventilation. The extra heat to warm that air belongs in the heat loss.
Done early, it is a small duct and a damper. Discovered at final inspection, it is a hole cut through a finished wall.
Big hood in the plans? Tell us the hood size. We design the makeup air with the ventilation and put it on the RMVDS.
Get Free Quote →It depends on how much air the hood exhausts, how tight the house is, and what else is in it. The 2024 Ontario Building Code added prescriptive requirements for makeup air (Article 9.32.3.8, per the Ontario Building Officials Association). A big hood in a tight new house is the classic case. Ask your designer to check it against the code before you buy the hood.
Outside air brought in on purpose to replace the air an exhaust fan pushes out. Without it, a tight house goes negative and pulls air back in wherever it can, including down a chimney or a furnace vent.
Houses got much tighter and range hoods got much bigger. In an old leaky house the air came back through a hundred cracks. In a tight house there are no cracks.
It helps, but the code and your inspector want a planned system, not a habit. And nobody opens a window in January.
Not for a big range hood. A balanced HRV brings in as much as it exhausts, so it does not replace what the hood pushes out. Makeup air is a separate system, often interlocked with the hood.
In an Ontario winter, cold air pouring into the kitchen is miserable. Most makeup air systems temper the air or bring it in where it can mix. That is part of the design, and part of the heat load.
Send your drawings and the hood size. We design the ventilation and makeup air together and put it on the RMVDS for your permit.