How to Calculate CFM Required for a Kitchen

The kitchen is a major source of air pollution in your home, frequently dispensing oil, grease, water vapor, plant chemicals and partly combusted gas, such as poisonous nitrogen dioxide, into the air. Efficient ventilation can remove these undesirable pollutants before they have time to cool and attach themselves to the walls and ceiling, or be inhaled by you and your family. Calculating how much ventilation you require, based on the size of the kitchen and the number of times you want to replace the air every hour, is a straightforward process.

Tape measure

Instructions

- 1
  Measure the length and width of the kitchen. If the dimensions vary, divide the kitchen floor area into rectangles and measure each one. For example an L-shaped kitchen consists of two rectangles, so measure them as separate areas.
- 2
  Convert measurements in feet and inches into decimal feet. Do this by multiplying the inches part of each measurement by 0.0833. This convert inches to a decimal fraction.
  
  For example 15 feet and 5 inches is equivalent to 15.4165 feet because 5 x 0.0833 = 0.4165.
- 3
  Calculate the surface area for each rectangle by using this equation: Surface area = length x width. Calculate this for each rectangle, and if more than one rectangle is involved, combine the surface areas of all the rectangles to obtain the total floor area.
  
  For example, an L-shape room consisting of a 10 x 10-foot rectangle and a 6 x 10 rectangle has a total floor area of (10 x 10) + (6 x 10). That's 100 + 60, or 160 square feet.
- 4
  Measure the height of the kitchen and convert the value into decimal feet. Multiply the height by the floor area to calculate the volume of the room.
  
  For example, a kitchen with 160 square feet of floor space and a ceiling 9 feet high has a volume of 1,440 cubic feet.
- 5
  Decide how many times you want to change the air in the kitchen every hour. For example, you may decide to change the air 10 times every hour.
  
  Multiply the number of changes by the volume of air in the kitchen to determine how much air is moved every hour. For example, 1,440 cubic feet of air replaced 10 times per hour is a total of 14,400 cubic feet.
- 6
  Divide the total ventilation per hour by 60 to find the volume of air moved every minute. Ventilation is measured in cubic feet per minute.
  
  For example, 14,400 / 60 = 240, so the system must displace 240 cubic feet of air every minute, or 240 cfm.

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