Kitchen ranges are a significant source of indoor air pollution. Gas ranges produce oxides of nitrogen, or NOx, and if they don't combust cleanly, they can produce carbon monoxide likewise. Both gas and conventional electric ranges interact with smoke, spatter, fumes, and vapors from cooking to produce clouds of small particles that are suspected of having wellness effects.

The point of kitchen frazzle hoods is to capture those combustion gases, vapors, and particles (along with odors) and transport them safely out of the house. Just kitchen exhausts—peculiarly the big units associated with commercial ranges—come up with their own set of issues. In particular, they tin can backdraft other appliances in the firm, such as natural-draft heating equipment and h2o heaters.

In 2009, the International Residential Code (IRC) was amended to require makeup air to be provided for any kitchen exhaust fan that exceeds 400 cubic feet per minute (cfm) in capacity. That requirement stayed in the lawmaking through the 2012 and 2015 editions. And then, in 2018, the code was amended again to limit the application of that makeup air requirement. The new language requires makeup air but if the house besides has atmospherically vented combustion equipment that could be backdrafted, such as a naturally vented h2o heater or a natural-draft furnace. An all-electrical house or a house with only sealed combustion equipment would be exempt from the makeup air requirement. Here'due south the language:

"Where i or more gas, liquid, or fuel-burning appliance that is neither direct-vent nor uses a mechanical draft venting system is located within a habitation unit'south air barrier, each exhaust system capable of exhausting in excess of 400 cubic anxiety per minute shall be mechanically or passively provided with makeup air at a rate approximately equal to the exhaust air rate. Such makeup air systems shall exist equipped with not fewer than ane damper complying with Department M1503.half dozen.ii."

Interestingly enough, the IRC has never required kitchen range hoods themselves. The provisions for makeup air are required when a high-capacity exhaust fan is installed, simply there is no rule in the model code really requiring any type of range hood.

That'due south not to say, all the same, that a land or local lawmaking tin can't crave an exhaust fan, and some do. Oregon'due south code, for example, provides, "Domestic kitchen cooking appliances shall be equipped with ducted range hoods or down-draft frazzle systems." Only Oregon requires only a pocket-size fan capacity: 150 cfm intermittent. Washington, by comparison, stipulates, "Frazzle shall be provided in each kitchen, bath, water closet, laundry expanse, indoor pond puddle, spa, and other room where water vapor or cooking aroma is produced." There is no mention of range hoods, and the required ventilation rate, again, is low: 25 cfm continuous, or 100 cfm intermittent.

In any case, large commercial-manner gas ranges typically are installed with powerful range hoods and for adept reason: Nobody using a big range would desire to be without the ability to capture and frazzle smoke, heat, steam, and cooking odors. Once a range hood capable of 600 cfm, 800 cfm, or one,200 cfm is in place, backdrafting of pressure-sensitive equipment is a hazard.

There are other reasons as well backdrafting to consider the demand for makeup air. In tight houses, exhaust fans are fighting against room pressures to move air. If in that location aren't enough leaks in the building envelope to supply makeup air, the fan may not effectively exhaust the kitchen air. In that example, the primary purpose of the fan is frustrated.

Broan's makeup air damper opens or closes in response to the control on the range hood fan, allowing passive entry of makeup air for the exhaust fan.
Broan's makeup air damper opens or closes in response to the control on the range hood fan, allowing passive entry of makeup air for the exhaust fan.

There are two kinds of solutions to providing makeup air: active and passive. Typical of the passive solution is the Broan Automatic Makeup Air Damper (come across photograph, above). The damper comes in three sizes (six inches, 8 inches, and 10 inches). The idea is for the damper to open up any time the exhaust fan is depressurizing the space. Broan offers a variety of command strategies for operating the damper: a "LinkLogic" connection that sends command signals over ability wiring, a direct-wired connectedness that communicates with the frazzle device through low-voltage wiring, and a Universal model that controls the damper by means of a pressure sensor at the exhaust device, connected to the damper via depression-voltage wiring.

Fantech's MUAS makeup air system includes ductwork, a filter, and an inline fan designed to supply the same amount of air used by the exhaust fan while maintaining a neutral pressure in the kitchen. MUAS sizes are available to match very large range-hood and downdraft exhaust fans.
Fantech's MUAS makeup air organisation includes ductwork, a filter, and an inline fan designed to supply the same amount of air used by the exhaust fan while maintaining a neutral pressure in the kitchen. MUAS sizes are bachelor to match very large range-hood and downdraft frazzle fans.

The Broan solution requires a force per unit area deviation to move air through the makeup air duct. An alternative to this strategy is the Fantech Makeup Air System, or "MUAS" (see photo, above). The MUAS incorporates an in-line intake fan to the air supply duct, calibrated to match the kitchen frazzle fan. Like the Broan damper, the Fantech equipment comes in a range of sizes to match various frazzle fan capacities: the MUAS 750, the MUAS 1200, the MUAS 1600, and the MUAS 2000 (the number corresponds to the maximum cfm of the fan). Controls enable the installer to gear up the system to operate at a neutral air pressure level, a slight positive pressure level, or a slight negative pressure. The system responds to the speed of the frazzle fan and ramps the MUAS fan upwards or downwards to match the frazzle airflows.

In cold climates, in-drawn air can crusade discomfort during winter. To compensate for this, Fantech offers an optional MUAH air heater that tempers the incoming air using electric resistance heat.

Range-hood manufacturers have responded to the lawmaking in another way: They've just provided the market with more hoods whose maximum exhaust airflow is under 400 cfm. The market is now full of range hoods whose maximum airflow is rated at 390 cfm. For most kitchen ranges, that's more sufficient to get the job washed.

So for builders who want to avoid problems, there'due south a pretty uncomplicated pathway: In new construction, stick to ranges that volition work well with less than 400 cfm of exhaust; stick to all electric or all sealed-combustion heating and hot-water equipment; and, to minimize the need for kitchen exhaust, consider installing electric convection ovens and electric consecration ranges. That combination should give you simple code compliance without makeup air, and reasonably effective performance across the board. The contraction, of course, is fireplaces: If you have a fireplace in a business firm with a powerful range hood, you probably want to include makeup air in your kitchen design.

Remodels, however, are some other thing. In many cases, a new kitchen with new cooking and venting equipment is built in a house with existing naturally vented heating equipment, such as a natural-draft water heater. The new range hood could button the water heater into a backdrafting situation. And as the old adage says, "If you don't test, you don't know."

Gary Boyer is a project manager for Border Energy in the Washington, D.C., suburbs. In his work verifying builder code compliance, Boyer says, it has been at least seven years since he's seen a naturally vented h2o heater in a new build. On the other hand, he says that in his combustion testing work, information technology'due south not uncommon to discover a new range hood threatening to backdraft an existing water heater in a remodeling situation. You could handle that trouble by installing makeup air for the kitchen. But Boyer says the mutual solution is to replace the water heater with a direct-vent model.