Keep in mind range hoods are usually not required by most local building codes, however cooking without them can lead to smoke and smells left in your kitchen. Check with your local county for any codes that would be required before starting your kitchen remodel. Here are a couple of measurements and tips before you start your project.
To properly calculate the amount of CFM’s (cubic feet per minute) for your range hood you’ll need the following:
Size of your range
Gas ranges you’ll need the total BTU’s (British thermal units)
Size of your kitchen (Width Length & Height)
Length & angles of ductwork being used
Range Size Calculation:
A basic rule used to determine your range hood would be for the hood to move a minimum of 100 CFM for every 12” of range width.
· Example a 30” range would be 2.5’ x 100 = 250 minimum CFM range hood
Gas Range BTU Calculation:
Gas ranges produce a lot more heat than electric ranges so gas ranges will require larger CFM requirements. You’ll need to combine each of the range burners to determine the total BTU’s for your range and divide the total by 100 to determine the correct CFM for your range.
· Example of a 5 burner range (1 x 15,000, 2 x 10,000, 2 x 5,000 = total of 45,000 BTU’s)
· 45,000 ÷ 100 = 450 CFM for the range
Kitchen Size Calculation:
Your kitchen size should also be considered when calculating CFM to help maximizing the correct amount of air flow within your kitchen. Range hoods should be able to exchange the air a minimum of 15 times per hour or once every 4 minutes.
· Example of a kitchen 16’ wide x 12’ length x 10’ high (16 x 12 x 10 = 1920)
· 1920 cubic foot room x 15 air exchange = 28,800 cubic feet to move per hour
· 28,800 ÷ 60 = 480 CFM for your kitchen
· Or total cubic feet of 1920 ÷ once every 4 minutes = 480 CFM
Every length, turn and cap in your ductwork adds resistance in air flow, there for these things must be noted to determine the correct amount of CFM required for your project.
When using an 8” round ductwork the following additions will be added.
· Add 1 CFM per foot of pipe length used.
· Add 25 CFM for every elbow being used.
· Add 40 CFM for roof caps being used.
· Example: 10 foot pipe length + 25 elbow + 40 roof cap = 75 CFM
The final calculation is to take the largest CFM rating plus the ductwork to determine the hood for your project.
Example of the above calculation:
Range size (250 CFM) Gas range (450 CFM) Kitchen size (480 CFM) and the added ductwork (75 CFM)
The following CFM would be required. Largest CFM was (480) plus ductwork (75) = total of 555 CFM as the minimum requirements for the project.
We hope that these measurements will help you figure out what you need. After reading this and you feel lost, please give us a call and we can help you with the specs and make sure that you are getting the right hood and appliances for your kitchen.