How to Provide Makeup Air for Range Hoods
If your kitchen has a powerful exhaust fan, it may be making your indoor air worse.
Synopsis: Range hoods are a necessity for evacuating kitchens of the smoke and odors that can accompany cooking. Most of the time, the indoor air the hood is exhausting is replaced by air entering the house through random spaces around doors, windows, or mudsills. With some big appliances and in tightly built, energy-efficient houses, though, range hoods can be detrimental because they have no air leaks to draw from. That can lead to the danger of backdrafting, or the introduction of exhaust gases from flues and chimneys. In this article, energy nerd Martin Holladay outlines various solutions that allow range hoods to function well in tightly built houses. You can bring makeup air into a tight house in three ways: through the HVAC system using dampers; through wall- or ceiling-mounted grilles; or through mechanized makeup-air solutions. Some tight homes also can benefit from the use of a heat-recovery ventilator (HRV) or an energy-recovery ventilator (ERV). Perhaps the most important consideration is to size the range hood properly from the start. A small range hood is often adequate.
When Cheryl Morris moved into her new home, she realized that the kitchen exhaust fan was probably too powerful. Whenever she turned on the 1200-cfm fan, strange things happened. “It pulled the ashes out of the fireplace, halfway across the room, right up to my husband’s chair,” she says. Those dancing ashes demonstrate an important principle: Large exhaust fans need makeup air.
The air that fans remove has to come from somewhere
Most homes have several exhaust appliances. They can include a bathroom fan (40 cfm to 200 cfm), a clothes dryer (100 cfm to 225 cfm), a power-vented water heater (50 cfm), a woodstove (30 cfm to 50 cfm), and a central vacuum-cleaning system (100 cfm to 200 cfm). The most…