When selecting a range hood, it is important to choose the correct size. CFM ... or cubic feet of air moved per minute ... is used to measure the size of a range hood. Selecting a range hood / blower's capacity needs to consider stove type, kitchen size, and ductwork. Let's look at how to determine CFM requirements
Electric Stove / Range - One simple calculation requires 100 CFM for every linear foot of stove width. For example, with a 30" wide electric stove, your hood should be rated at 250 CFM or higher. This is calculated by taking the stove width (30" equals 2.5 linear feet) times 100 CFM per linear foot.
Gas Cooktop - Compared to an electric stove, gas cooktops give off substantially more heat. Consequently, a larger hood is required. The first step in determining the necessary CFM is totaling the BTU's for all the burners. Typically, each gas burner will be between 5,000 to 15,000 BTU's. The output for a four burner gas cooktop will normally be around 40,000 BTU's. Divide the cooktop's total BTU's by 100 for the CFM requirement. For a standard gas cooktop, a 400 CFM hood / blower (40,000 ÷ 100) would be needed.
Kitchen Size -- You also need to consider the size of your kitchen. The larger the room, the larger the range hood. Industry guidelines call for turning over the air in a kitchen 15 times per hour. This is once every four minutes. To determine CFM, take the volume of the room (width x length x height), multiply by 15 exchanges per hour, and then divide by 60 minutes per hour. For a 12' x 16' room with 9' ceilings, the necessary CFM is 432 (12 x 16 x 9 x 15 ÷ 60 = 432).
Ductwork - As air flows through ductwork and around corners, its progress is hindered. This needs to be considered in sizing the range hood blower. Guidelines call for adding 1 CFM for every foot of ductwork and 25 CFM for each turn. If the hood is vented through a roof cap, an additional 40 CFM needs to added.
After calculating CFM using these different methodologies, size your range hood based on the largest CFM requirement and then add for ductwork. This will result in the correct size for your home's range hood.
If you have more questions about remodeling or range hoods, please stop in our Carmel, Indiana showroom and talk with one of our designers. They will be happy to help.