## How to Calculate Kitchen Range Hood Fan Size

##### By: Danny Lipford

Kitchen range hoods that are vented to the outside are a great way to remove heat, odors, moisture, and smoke from your home when cooking. The fans in range hoods are rated by the cubic feet of air they move per minute (CFM), and it’s important to buy a range hood that moves enough air to be effective. Below are several different ways to calculate the CFM for a range hood.

### Range Hood Fan Size

The basic rule of thumb when determining the fan size of a range hood is that it should move a minimum of 100 CFM of air for every 12” of stove width. So if you have a 30” wide stove, you would need a range hood with a fan that moves at least 250 CFM of air:

2.5′ wide stove x 100 = 250 CFM minimum range hood fan size

### Room Size

You should also take into account the size of your kitchen in cubic feet when calculating the size range hood fan needed, since a larger kitchen needs more venting to clear the air than a smaller room.

A range hood should be able to exchange the air in the kitchen at least 15 times per hour or every four minutes. For example, if your kitchen is 16’ long x 16’ wide with an 8’ ceiling, it would contain 2,048 cubic feet of space:

16’ wide x 16’ long x 8’ high = 2,048 cubic feet

To find the fan needed for your size kitchen, multiply the number of cubic feet in the room by the number of air exchanges (15), then divide by the number of minutes in an hour (60).

For example:

2,048 cubic foot room x 15 air exchanges = 30,720 cubic feet moved per hour

30,720 cubic feet ÷ 60 minutes = 512 CFM range hood fan or higher

An easier way to make the calculation above is to divide the number of cubic in the room by four minutes:

2,048 cubic foot room ÷ 4 minutes = 512 CFM range hood fan or higher

### Gas Stove

The burners on a gas stove produce a lot more heat than those on an electric range, so a kitchen with a gas stove requires a larger capacity range hood vent fan.

To calculate the fan sized needed for a gas stove, combine the BTU ratings for all the burners on your stove (gas burners range from 5,000-15,000 BTU per burner, with an average of about 10,000 BTU per burner and a total of about 40,000 for a standard 4-burner stove), then divide by 100 to find the minimum CFM needed for a kitchen with a gas stove. For example:

40,000 BTU gas stove ÷ 100 = 400 CFM range hood fan or higher

### Range Hood Ductwork

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

When using smooth, round 8” diameter, metal pipe, add one CFM per foot of pipe, plus 25 CFM for each elbow, and 40 CFM for a roof cap.

For example, if the vent pipe was 10’ long with two elbows and a roof cap, you would need to add 100 CFM more to the fan size ratings above:

10 pipe length + 25 elbow + 25 elbow + 40 roof cap = 100 CFM

### Calculating Range Hood CFM Vent Fan Size

To make the final calculation, take the larger of the CFM rating for stove width, room size, and stove burner. Add the additional CFMs needed for the ductwork to arrive at the minimum CFM range hood to buy.

In the examples used above, if your kitchen has a 30” stove (250 CFM minimum) in a 16’ x 16’ x 8’ room (512 CFM minimum), and a 40,000 BTU gas stove (400 CFM minimum) you would want a fan rated at 512 CFM or higher, plus 100 CFM for the ductwork for a total of 612 CFM or more.

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#### 29 Comments on “How to Calculate Kitchen Range Hood Fan Size”

• Rob Says:
August 24th, 2016 at 12:28 pm

The range hood sizing in this article is for commercial kitchens, not residential, and will lead a homeowner to grossly oversize range hood ventilation, unless you plan to cook 8-10 hours a day, every day. The sizing calculations indicated here could lead to dangerous backdrafting of other appliances, which is why code now calls for any range hood over 400 cfm to include makeup air, (also not mentioned here) which is generally a huge energy penalty. The Home Ventilating Institute recommends 40 (thats forty. four zero.) cfm per foot of cooktop, meaning that most homes will need a range hood of less than 200 cfm. See this article from Home Energy Magazine: http://homeenergy.org/show/article/year/1999/magazine/113/id/1448

• David Says:
August 5th, 2016 at 1:45 pm

Thanks for the information. Maybe I missed in the comments anything about factoring in the height above the stove. I have an island unit being installed and the glass hood is at my head (and it hurts). The installer believes he can modify it to install higher but I wonder how effective the unit will be then. Do I need a higher cfm fan to mount it higher?

• Don Says:
June 17th, 2016 at 11:12 am

Fan has a 6″ vent pipe can I reduce it to 5″

• augustine carrasco Says:
February 29th, 2016 at 5:22 am

Please, when quoting ASHRAE requirements. Add handbook year and paragraph. Avoid being sloppy in respect to the ASHRAE organization members.

• Rosemary Gray Says:
January 31st, 2016 at 7:52 am

Great information.

• jeannie Couturr Says:
December 27th, 2015 at 4:15 pm

our under cabinet hood range is 1/8″ too big to fit between the cupboards. what do we do? The cabinets are oak. we wanted to replace the 28 yr old hood to match our new appliances. Any help appreciated.

December 9th, 2015 at 4:46 am

hai ajis khan

you required 2215 fresh air and 2768 exhaust air

December 9th, 2015 at 4:40 am

as Per Ashare Handbook
500 l/s-meter square for exhaust kitchen hood duct

• GM Says:
November 5th, 2015 at 11:02 am

For an open concept home, how do you calculate the room size? Do you just use the measurements for the kitchen area minus the breakfast nook and family room or should those be included?

• Green Builder Says:
October 2nd, 2015 at 10:19 pm

How many cfm does a wall vent cap require? Presumably fewer than 40 for a roof cap?

• Ehtesham Quibria Says:
September 30th, 2015 at 9:31 pm

Very nice info. My question is; what will be the ducting losses for 4 inch chimney?

• ajis khan Says:
September 9th, 2015 at 5:56 am

Hi,
I want to know CFM of Kitchen Exhaust hood. Still I am thinking how to to find out?. i have L= 3100mm X B= 800 mm x h=600. How to calculate, can you tell me please…

• HAYWAI Says:
September 8th, 2015 at 10:02 pm

Thanks so much for this piece of useful info. Pls I’ve gotten a (4.2 x 16.9 x 2.7)m hotel kitchen with four electric cooker control units to deal with in terms of range hoods so kindly advise me on the size and number of extractor fans I’ll need. Thanks!!!

• Sara Says:
August 6th, 2015 at 2:00 pm

I have just moved into a new home and chose not to have the builders install a range hood as I plan to purchase a chimney style myself. We were told by the kitchen design company that by the builders standards we can only get a one with 350 CFM or less. Why would this be? We have 9′ ceilings, and the vent is about 6″ from the ceiling and vents directly to the outside (no turns etc). We’re in a 2600 square foot home with our kitchen wide open to the great room, and not only is a fan under 350cfm difficult to find, I also fear it won’t be enough for the large space.

• Ben Erickson Says:
August 5th, 2015 at 5:09 pm

Mark,
Glad to hear out article on sizing a range hood was of help!

• Mark Says:
August 5th, 2015 at 10:33 am

Great article! As a Kitchen Remodeling Designer this will help me in giving advice to my clients.
Thanks!

• Lisa Says:
June 14th, 2015 at 2:26 pm

We are remodeling a house and installing a microwave above the freestanding 30″ stove. We will vent from the stove to the microwave through the ceiling then in between the joists and on through to the outside. Only one turn to go through joists then straight piping (around 20′) to the outside. My question is: What size piping to use–We thought maybe 6″??

• Robbyn Says:
May 1st, 2015 at 10:00 am

My question is I’m replacing this good for nothing kitchen exhaust fan. The physical size of existing fan is enormous, 42 inches can I go to a smaller size. But have the CFM higher.

• Amin Says:
April 29th, 2015 at 2:35 am

Great! U have shared the knowledge in very simple method. Easy to understand, Thanks.

• Tesfaye Bekele Says:
February 7th, 2015 at 10:10 am

I highly appreciate if somebody tells me the ideal height of a kitchen hood height in a commerical cooking firms? How tall should it be (at the main cooking station from the floor? Thank you

• Peter Says:
January 27th, 2015 at 5:48 am

just confirmed the approach with what I’ve learnt over time and its just PERFECT!

• Al G. Says:
January 21st, 2015 at 11:29 am

the world will be a easier and better to live if all the people would be like you that share their knowledge and expertise. THANK YOU SO MUCH FOR SHARING. INFO IS VERY HELPFUL.

• malhotra Says:
January 8th, 2015 at 9:12 pm

if our kitchen size is 10’x13’x9′ which type of chimney i’ll choose if our gas stove is of 4burner

• Abhai Singh Says:
October 11th, 2014 at 5:58 am

I have 4″dia straight chimney duct going through the wall to the top of roof at a height of 25 feet from chimney hood. What will be pressure drop across the chimney duct & what capacity chimney is required to send the exhaust at the rof top.

• kanakaraju Says:
September 21st, 2014 at 1:31 am

HI ,
My Name is Ch.kanakaraju ,
I Small Request Central Star hotel Kitchen Ranger area hood How Much CFM Required ,
Kitchen Cooridor Area Exhaust Grill How Much CFM required
Dish WASH area How exhaust CFM Required .
I need THUMB RULE
Thank u , so much
Ch.kanakaraju

• Brandon Says:
August 31st, 2014 at 4:01 am

Wow! Helpful info, I was wondering how it worked. I got a result on a calculator I found on the internet and didn’t know if it was right or not. Turns out it was good. I wish they add the duct work elbows, etc too. Thanks for all the help Danny!

• osama Says:
August 29th, 2014 at 7:59 am

thank you on explain. Please can send standard of gas stove?

• Duke Lawrence Says:
July 15th, 2013 at 4:43 am

I find the info very useful

• Steve Cross Says:
March 23rd, 2013 at 4:32 pm

Notably absent from your show and your site…a make-up air unit to counter the negative pressure effect that range hoods often contribute to.

Especially important considering clothes dryers, older lower efficiency gas furnaces, gas water heaters, and bathroom exhaust fans already induce back-drafting conditions.

Of course that may be less of a concern with older leaky houses but could be dangerous in homes retrofitted with better insulation and updated windows…essentially the tighter structures.

Just thought I’d mention the omission.

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