Kitchen range hoods that you vent to the outside are an effective way to remove heat, odors, moisture, and smoke from your home when cooking. The trick to buying just the right one is getting the correct size, which is related to the cubic feet of air the hood fans move per minute (CFM). It’s important to buy a range hood that moves enough air to ventilate your kitchen effectively. Here’s what you need to know in order to find the right one for your kitchen, including measuring your stove width, knowing your kitchen size, and calculating the total CFM.

## Calculate Stove Width

The rule of thumb for range hood fan size is it should move 100 CFM of air for every 12 inches of stove width. If you have a 30-inch wide stove, you would need 250 CFM.

Here’s the calculation: 2.5-foot wide stove x 100 CFMs per foot = 250 CFM

## Kitchen Size Matters

You should also account for kitchen size in cubic feet. Larger rooms need more venting to clear the air. A range hood should exchange the kitchen air at least 15 times per hour or every four minutes.

Begin by calculating the size of your kitchen. If your kitchen is 16 feet long and 16 feet wide with an 8-foot ceiling, it would measure 2,048 cubic feet.

You can then determine the fan CFM needed by dividing the total cubic feet by 4.

Here’s the calculation: 16 x 16 x 8 = 2,048 cubic feet (kitchen size) ÷ 4 (exchanging kitchen air every four minutes) = 512 minimum CFM.

## Gas Stove Considerations

Gas stove burners produce more heat than electric burners do, so gas stoves require a larger fan. To determine the needs for your gas stove, you need to first begin with your stove’s BTU ratings. Combine the ratings for each burner and then divide by 100 to determine the minimum CFM. Typically, gas stove burners range from 5,000 to 18,000 per burner. On average, older 4-burner stoves have a total BTU of 40,000, but more modern stoves with professional settings or more than four burners may have higher BTU ratings.

For a kitchen with a 40,000 BTU stove, the calculation would be as follows:  40,000 BTU stove ÷ 100 = 400 CFM

## Ductwork Factors

The size, shape, length, turns, and cap on the range hood ductwork add resistance. This reduces the amount of air the vent fan can move, requiring additional CFM for the fan.

If you are using a smooth, round 8-inch diameter metal pipe, you should add one CFM per foot of pipe, plus 25 CFM for each elbow and 40 CFM for a roof cap.

For example, if you have a 10-foot-long pipe with two elbows and a roof cap, this is the additional CFM calculation: 10 (10 feet of pipe x 1 CFM per foot)  + 50 (2 elbows x 25 CFM per elbow) + 40 (1 roof cap x 40 CFM per roof cap) = 100 total additional CFM

## Calculating Total CFM

Finally, you need to compare the CFM ratings for your range size, room size, and gas stove BTU ratings. Choose the option that requires the largest CFM and then add the ductwork CFMs to determine your minimum CFM required.

Using my earlier examples:

• 30-inch stove = 250 CFM
• Room size = 512 CFM
• 40,000 BTU gas stove = 400 CFM
• Ductwork = 100 additional CFM

Because the room size has the highest CFM requirement, we add the additional ductwork CFMs to this number.

512 CFM + 100 CFM = 612 CFM

Therefore, the minimum CFM for this example kitchen range hood fan is 612.

## So, Is Calculating Range Hood Fan Size Complicated?

Calculating a range hood fan size isn’t complicated, but it does require some math. You’ll need to know your stove width, the size of your kitchen in cubic feet, your stove type, and your ductwork length to determine the CFM rating for adequately ventilating your kitchen.

Range hood brands also provide CFM guides. However, I suggest working with the numbers for your specific home since the number listed on your range hood may not meet the recommendations for the size of your kitchen and your specific stove type.

## FAQs About Calculating Kitchen Range Hood Fan Size

### How do I measure kitchen cubic feet to calculate CFM?

Multiply the length of your kitchen by its width and its height. If your kitchen is an open concept, use only your kitchen area.

### What if I don't know my gas stove's BTUs?

If not specified, assume 10,000 BTU per burner or 40,000 total for a typical 4-burner stove. It’s always better to overestimate your BTUs, especially if you have a professional stove setup.

### Can I install a higher CFM hood fan than what’s required?

Yes, exceeding the minimum CFM is fine and provides more ventilating power.

### How accurate do my measurements need to be?

It’s best to get the exact measurement for your stove’s width. Measurements for your kitchen’s size should be accurate to 6 inches or less.

### Q: Does a higher CFM range hood mean more noise?

Not necessarily. Well-designed fans on higher CFM models can move large volumes of air while keeping sound levels low by optimizing blade and blower configurations.

Editorial Contributors

Nikki Stavile

Nikki Stavile is a writer based in Tucson, Arizona. As an avid backpacker and passionate environmentalist, her work often focuses on sustainable movements at the personal and societal level.