Determine CFM Requirement

Determining CFM Requirements*
(Based on BTU’s and Other Factors)
For Trade-Wind
®
Professional & Standard Series Liners and Hoods
Calculating CFM Requirements
There is no “industry standard” criteria for determining how many CFM’s are required for the many different types
of stoves and ranges. Every installation has many variables including the basics: distance between hood and
cooking surface, island or wall installation, air currents in the kitchen, length and shape of the duct run, e.g.,
number of bends (elbows), type of damper, type of roof cap and “make-up air” considerations.
Other variables include the user’s preference for amount and types of foods cooked, e.g., fish vs. steamed
vegetables. Cooking with strong smelling seasonings such as curry can actually cause an entire house to smell
of curry, which can negatively affect the resale value of the house. And given that indoor grill cooking generates
large amounts of smoke, cooks that grill indoors should install hoods or liners with very high CFM performance.
Given that most cooks will seldom have all burners and the oven set on “high”, installing range hoods with less
CFM capacity than indicated by the following BTU-CFM calculation is a common practice. Remember, the
overall objective is to get the HOGGSS out of the kitchen (Heat-Odors-Gasses-Grease-Steam-Smoke), so the
CFM needs for a specific installation are also a function of the cooking practices of the homeowner.
To determine the amount of CFM needed to exhaust an electric, gas or dual fuel range, a generally accepted
“rule-of-thumb” is to divide the total BTUs by 100.
Example: KitchenAid’s Architect
®
Series, Dual Fuel 36” Range
6 Surface Burners (Gas)
72,000 BTU’s
Broiler Element (Electric)
3,000 Watts x 3.5 = 10,500 BTU’s
(BTU Equivalent; see details below)
10,500 BTU’s
Total BTU’s
82,500
Rule-of Thumb CFM Requirements
82,500 divided by 100 = 825 CFM
So…What is a Watt? What is a BTU? How do you Convert a Watt to a BTU?
When determining the performance requirements of a particular range hood installation, it is good to know some
comparisons of heating terms between electric and other fuels. Most fuels besides electricity are measured in
BTUs. Gas ranges, fuel oil furnaces and kerosene heaters all are rated with BTUs. Electric ranges however, are
measured in watts.
BTU is the acronym for British Thermal-Unit, a unit of measure of the energy in various fuels. One BTU is the
amount of heat needed to raise the temperature of 1lb of water 1 degree Fahrenheit. To convert watts to BTUs,
the formula is to multiply the total number of watts by 3.5 to get the “equivalent amount” of BTUs that will be
created by an electric range.
For example, a range with…
- 2, eight-inch 2,000-watt elements and (4,000)
- 2, six-inch 1,500-watt elements and (3,000)
- 1, broiler element rated at 10,000 watts (10,000)
…has the equivalent of 59,500 BTU’s (17,000 watts x 3.5 = 59,500 BTU’s). In this example, using the rule-of-
thumb, the 59,500 BTUs would indicate the need for a range hood with at least 595 CFM (59,500 / 100).