Sunday, November 24, 2013

Range Hood - The BTU,CFM, width and kitchen size.

After each cooking session, grease stain is one of the unpleasant remains and because cooking generate fumes and heat, a lingering stagnating odor would remain in the kitchen.The range hood function is to filter the smoke, fumes, grease, steam and carbon monoxide from the air while we are cooking. The most important thing to consider before buying the range hood is to determine the suitable size.

Sizing the Range Hood

The airflow capacity of a range hood is measured in CFM, or cubic feet per minute.

The first method would be sizing the range hood to BTU.

Question No 1 : What is BTU?

Answer : BTU is actually the abbreviations for British Thermal Units.  One BTU is the amount of thermal energy required to raise the temperature of a pound (0.45kg) of water by one degree Fahrenheit(0.56 degree Celcius).

Question No 2 : How many BTU in a stove?

Answer :  Most manufacturer list their stove as BTU per hour. The higher the BTU, the hotter the stove. A home stove has, on average, about 7,000 BTUs per burner. For comparison, a candle flame puts out about 100-300 BTU/hr, backyard barbeque creates 25,000 BTU/hr.

The recommendation by the Home Ventilating Institute (HVI) is to divide the BTU rating of your stove by 100 to arrive at a minimum guideline for CFM rating. If the cooking equipment is conventional then the cooktop is less than 60,000 BTU or if the equipment is high performance then the cooktop is over 60,000 BTU.For example

The BTU for each burner on the conventional stove is 7,000 BTU. There is 4 burner on the stove, total BTU would be 

7,000 x 4 = 28,000 BTU

To measure the CFM, 

28,000 BTU / 100 = 280 CFM

So this indicated your Range Hood must be at lease 280 CFM or greater.

The second method would be sizing a range hood based on the width of your range. Basically its 100 CFM per foot of cooktop width. Example: 36" wide wall application indicates a need for 300 CFM.For example if the stove sit against a wall, Home Ventilating Institute (HVI) recommended 100 CFM per linear foot of the range. For example, a 24 inch (60 cm) range would require a hood rated at 200 CFM or greater. 

24 inch (60 cm) range = 200 CFM

30 cm is considered as one(1) foot.

For island installation, more CFM is needed. For conventional cooktops use 150 CFM per foot of cooktop, and for high performance cooktops add 100 CFM to the estimate.So, a 24 inch (60 cm) range on an island needs 300 CFM of airflow.

The third method would be sizing a range hood based on kitchen size.The
HVI also recommends that your range hood should be capable of cycling the air in your kitchen completely 15 times per hour. This equates to a complete cycling of air every 4 minutes.

  • Begin by measuring the floor area of your kitchen. In a rectangular-shaped room, this can be done by multiplying the width and length. For example, a 10 ft x 10 ft kitchen has a floor area of 100 square feet.
  • Calculate the total volume of your kitchen. This is done by multiplying the floor area by the ceiling height. For example, if a kitchen has 100 square feet of floor area and a ceiling height of 8 feet, the total volume is 800 cubic feet.
  • Divide the total volume by 4 to get the required CFM rating. A kitchen with a volume of 800 cubic feet would need a range hood with a rating of (800 / 4) or 200 CFM.

  • Floor area          : 10 ft x 10 ft = 100 square ft

    Kitchen Volume   : 100 square feet x 8 feet ceiling height = 800 cubic feet

    Required CFM      : 800 cubic feet / 4 = 200 CFM

    After all the range hood size calculations based on BTU, width of range and kitchen size, choose a model with the highest CFM, even if it is more than needed. 

    For example : 

    BTU Heat Output requires 280 CFM

    Range Size requires 200 CFM

    Kitchen size requires 200 CFM

    In the above example, choose the highest CFM at 280.


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