The sales pitch by range hood manufacturers has been “bigger and faster is better.” Bigger, faster range hoods remove more vapors that come off a cooktop or a range more quickly. However, in today’s more insulated homes, powerful range hoods can produce unbalanced air pressure and suck flammable gases that ordinarily would vent to the outside back into the home. This increases the risk of carbon-monoxide poisoning, according to International Code Council, which is a building-safety group.
The 2009 International Residential Code (IRC) requires residential vented range hoods that have blower speeds of more than 400 cubic feet per minute (cfm) to include a system for creating makeup air to replace the air that’s pulled through the range hood and exhausted to the outside. As of press time, state or local governments in 29 states adopted the 2009 IRC, according to Home Ventilating Institute.
Martin Holladay, who is a residential-construction expert at GreenBuildingAdvisor.com, says you should check local building codes and determine whether your home has a sealed-combustion gas appliance, such as a water heater or a gas-burning fireplace. A sealed-combustion gas appliance is vented to the outside through a separate sealed vent.
If appliances aren’t sealed, you’d have to purchase a range hood that has a low cfm, or you’d have to buy a makeup-air system, which will cost you at least $980 including installation. (Installation can run as high as $1,500 in older homes, experts say.)
MAKING IT UP. Since 2010, several range hood manufacturers have produced makeup-air systems that are a simpler and less expensive alternative to a contractor-installed makeup-air system.
Broan-NuTone, Elica, Faber, Miele and Zephyr Ventilation now sell so-called cfm-reducer kits, which are marketed under different names but operate essentially the same. The kit includes an adapter that’s installed at the duct exit of a range hood. The adapter seals off part of the airflow via a round or square metal plate. This reduces the speed by which air is exhausted to the outside to below the required level without diminishing the effectiveness of the range hood to draw vapors from the cooking surface, manufacturers say. The kits range in price from $30 to $130, depending on the manufacturer.
But some experts tell Consumers Digest that such cfm-reducer kits amount to only half of an adequate makeup-air solution.
“The reducer reduces the flow of air, but it doesn’t eliminate the air-pressure problems,” says Brett Dillon, who is a managing partner of IBS Advisors, which is an energy-efficiency consulting company. Dillon says cfm reducers also could cause the performance of the range hood to decline to an insufficient level depending on the cooktop or range that you use. He says a range hood should provide 1 cfm of blower speed per 100 Btu of cooktop or range.
Jeremy Snider of Zephyr says you shouldn’t use a cfm reducer with just any range hood. He says Zephyr’s cfm reducer will reduce a range hood’s blower speed by 25 cfm. Reducing a range hood any further, he says, would affect how well the range hood vents the burners. Consequently, Zephyr recommends that consumers install a makeup-air system if they buy a range hood that has a blower motor of faster than 600 cfm, Snider says.
The Next Generation
Amana and Broan-NuTone now make automatic makeup-air dampers as a consumer solution. An air damper is inserted into the home’s forced-air duct system. (This involves cutting ductwork to insert the damper.) The damper opens automatically to replace the air that’s exhausted to the outside by the range hood. When the range hood fan turns off, so does the damper.
Although consumers might want to hire a contractor to install the damper, which, of course, will increase the cost, Broan-NuTone says its makeup-air dampers were designed so a homeowner could do it himself/herself.
These dampers come in different sizes to account for different range hoods and range in price from $165 to $360, depending on the manufacturer.