Sizes of exhaust fans available:
The size of an exhaust fan influences its cooling capacity and affects its ability to effectively clear grease and other cooking byproducts. Initially, exhaust fans used to be rather inconspicuously installed in kitchens but have now moved out into the open. In addition, newer models are much more powerful than their predecessors.
Earlier, kitchen fans had a capacity of exhausting 100 cubic feet per minute (CFM) of air. Then came fans with a capacity of 350 CFM. Nowadays, most kitchen fans on the market have an exhaust capacity ranging from 600 to 1,500 CFM. Manufacturers are even selling fans with an exhaust as high as 2,400 CFM for residential use.
Drawbacks of large exhaust fans:
Using a very large fan is equivalent to having a huge vacuum cleaner attached to the kitchen range on the outside of the house. The vacuum created by the fan removes air from the house, which lowers the pressure inside the house. With increasing depressurization, other appliances installed for exhaust purposes like fireplaces, furnaces, boilers, heaters, etc. begin to backdraft or pull fumes back into the house. For example, the smoke in a backdrafting chimney is sucked by depressurization back down the chimney.
Backdrafting is not only undesirable, it is also extremely dangerous according to the Consumer Products Safety Commission. Backdrafting has caused a number of deaths due to carbon monoxide poisoning.
The importance of providing makeup air:
The safe operation of any fan requires that the air removed from the house must be replaced. The Uniform Mechanical Code (UMC), therefore, requires the use of makeup air for commercial kitchens. Makeup air is air that is pushed out or pulled into the building intentionally. For makeup air to be effective, it must be almost equal to the amount of air that is exhausted by the kitchen fan.
Makeup air helps eliminate fuel spillage and backdrafting from vented combustion appliances such as gas water heaters or fireplaces. Another benefit of makeup air is that it ensures that the fan can actually function at its full capacity. When the fan runs at less than the rated capacity, it does not maintain sufficient air velocity to trap the various emissions from the cooking surface. The temperature of the makeup air can be controlled (made warmer or cooler) according to the comfort of the kitchen staff.
Exhaust fans are crucial to maintaining good air quality indoors. Installing the right sized fan for your kitchen and providing makeup air can go a long way towards saving energy and maintaining comfortable temperature conditions in your home.
