What Is Make-Up Air for a Range Hood?

Make-up air is fresh outdoor air brought into the house to replace what a range hood blows outside. A powerful hood can move a lot of air, and if the home cannot let that much back in, the hood effectively tries to pull a vacuum on the house, which causes real problems.

Why strong hoods need it

A well-sealed modern home does not leak enough air to feed a high-output hood. When the hood runs, the pressure inside drops, and the house pulls air back in through whatever paths it can find, including the flues of other combustion appliances. That can backdraft a water heater or fireplace and pull combustion gases the wrong way.

The signs you are short of make-up air

• Exterior doors are hard to open, or pop, when the hood is running.
• A whistling or draft at gaps around doors and windows.
• A fireplace, water heater, or furnace that backdrafts when the hood is on.
• The hood seems to run hard but never quite clears the kitchen.

What to check

• The hood’s rated airflow (CFM) versus how tight and how large the home is.
• Whether there are other combustion appliances sharing the same air.
• Whether a renovation is the moment to rough in a dedicated make-up air path.

When to call a sheet metal contractor

The best time to handle make-up air is during a kitchen renovation, while the walls are open. I check the hood against the house and rough in a make-up air path where the numbers call for it, so the hood can pull properly and the rest of the home stays balanced and safe.