Sizing an Exhaust Fan
Sizing an Exhaust Fan TIPS
- Different rooms require minimum amounts of air
- Kitchens need twice as much air as bathrooms
- WATCH exhaust fan videos below!
- Exhaust air out the roof except in heavy snow areas
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Size Is Everything!
Can you imagine trying to cool yourself on a hot summer day with just the air that's allowed to pass through a tiny cocktail straw? Just a tiny stream of air would pass through and it would be virtually worthless.
Move The Air
To cool something or provide enough air to keep things fresh, you have to move air. The room you're trying to ventilate dictates the amount of air that needs to be moved in a given amount of time.
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Air Movement Guidelines
For years the Home Ventilating Institute said that all the air in a kitchen should be changed out for new at least fifteen times an hour. They felt that bathrooms should have a complete air change eight times an hour.
Shhhhhhhhsss! Quiet Fans
Are you upset with how loud some bathroom or kitchen exhaust fans are?
Did you know you can get wonderful fans for bathroom exhaust where the fan is way up in the attic and there's no noise in the bathroom while the air is being sucked out of the room?
It's possible! Look at the following fan I installed in my own home:
Here's a typical Fantech bath exhaust fan setup. The odd cone-shaped metal thing is the fan. The two boxes that have the round white covers are place up in the ceiling joists of the bathrooms. All you see are the sleek round white covers. They come with and without lights! I LOVED these in my last house. CLICK THE IMAGE TO BUY the SET NOW.
A Fast Example
Let's take a small kitchen for an example. Say the kitchen measures 10 feet by 12 feet with an 8-foot ceiling. Remember how to compute cubic feet in a room?
You multiply length times width times height: 10 feet X 12 feet X 8 feet
That computes to 960 cubic feet of air in the room.
The minimum requirements say that this air should be changed 15 times an hour.
You now need to multiply 960 X 15.
This means that a fan must have the ability to move 14,400 cubic feet of air in an hour.
Exhaust Fan Videos
Watch these helpful videos about exhaust fans and how to vent them out of roofs.
The following video shows you how to prevent roof leaks around bathroom exhaust vents.
Fans Are Rated Cubic Feet Per Minute Not Hour
Since there are 60 minutes in an hour, we must divide the 14,400 by 60 to get CFM (cubic feet per minute).
Divid 14,400 by 60 and you get 240 CFM. Nothing to it!
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Handy Table For Fan Values
The following table does lots of the math for you. All you need to do is calculate the square feet of a room and the table tells you the CFM for either a kitchen or bathroom.
Square feet is easy. Just multiply the length of the room by the width. The table assumes a common 8-foot ceiling height.
The room area is listed in square feet. All values below the listed room size represent the fan's minimum capacity shown in cubic feet per minute.
| Room Area in Square Feet | Fan Capacity in CFM for a KITCHEN | Fan Capacity in CFM for a BATHROOM | Fan Capacity in CFM for Other Rooms |
| 35 | N/A | 40 | N/A |
| 45 | N/A | 50 | N/A |
| 55 | N/A | 60 | 45 |
| 65 | N/A | 70 | 55 |
| 75 | 150 | 80 | 60 |
| 85 | 170 | 90 | 70 |
| 95 | 190 | 100 | 80 |
| 100 | 200 | 110 | 80 |
| 125 | 250 | 140 | 100 |
| 150 | 300 | 160 | 120 |
| 175 | 350 | N/A | 140 |
| 200 | 400 | N/A | 160 |
| 225 | 450 | N/A | 180 |
| 250 | 500 | N/A | 200 |
| 310 | 620 | N/A | 250 |
| 375 | 750 | N/A | 300 |
| 435 | 870 | N/A | 350 |
| 500 | 1,000 | N/A | 400 |
| 560 | 1,120 | N/A | 450 |
| 625 | 1,250 | N/A | 500 |
| 685 | 1,370 | N/A | - |
Table Values courtesy of Nutone, Inc.
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Column B98
What size (CFM) remote kitchen exhaust fan should I use to properly vent a 4- burner gas cooktop? The distance from the exhaust above the stove to fan on the outside wall is 14 feet and there are 3 x 90 degree bends to get to the outer wall to vent.
Does an induction cooktop require less CFM venting?
Thanks
What do the fan manufacturers' charts say??????????
kitchen is 8'x8' and 10 ft high.ie say 650 Ccu ft of air.air is to be changed 15 times an hour. therefore fan must move650x15 equuals to
say10000times. on dividing by 60, we get160cfm
pl advise will 150 cfm will be sufficent or shud igo higher cfm
is dimension fan meaningfu like 6'/8'/10'/12' size or shape square / square/ is relevant
Pl advise on urgent basi and oblige.
Thank you
Hi, I am working on a school project, how to design a heating and cooling for a commercial building of 60, 000 sq ft. Any commercial building will do, I am planning on design a system for a super market, I don't how to start this project, perhaps you can give me some ideas thanks.
I want to design a machine , which needs exhaust fan . This machine should be placed in lawn or some open area to capture the air surrounding that machine. How will I know the capacity as amount of air is not known
I have a 10 by 15 by 8 room that I would like to know how many CFM exhaust fan I will need. Will be used to clear cigar smoke
Thanks
I'd go with a 300 CFM fan since it's foul cigar smoke.
Hi there I'm looking to put an exhaust fan in my garage above my poker table to clear cigarette smoke. My garage is 28'x28'x10' What size of fan would you recommend?
Oh, this is so simple. Just do the math and use the table above in the column. I show you above how to do the math. Since you want to exhaust cigarette smoke, I'd pick one that can do at least 1,000 CFM. Here's a great one:
http://amzn.to/2wmz7zx
I have cathedral ceilings in my home. The living room and dining room and kitchen are all cathedral. I would say about 900 sq ft. It gets really hot in the summer time and I'm thinking of putting an exhaust fan in one side of my peaks. I don't know right off hand what the cfm is but could you recommend something please? I'm at my wit's end at this point. I've burnt the blower motor in my ac unit and right now staying at a family members house until I can get it fixed. Thanks
never understood this line of thinking. what would you rather hear? white noise from a fan or the sound of someone going number 2? i always choose the loudest fans out there
I have a kitchen ceiling exhaust fan it came with the house (older home) it is grease covered and dirty and still works but it looks terrible and I do not feel it is doing a whole lot to exhaust cooking fumes and smoke from the kitchen and the there is grease on the blades which I have tried to clean several times inside and out but no luck. I thought why not just replace it and make it work better for us. How do I measure it to replace it and how much power is needed to exhaust a medium size kitchen space I want to purchase it before the worker comes out to replace it with a new one? Thank you.
You just measure the space between the existing cabinets. Take a photo of it and go to a store that sells new vent hoods. The column above tells you how many CFM the fan should have.
I need to ventilate a small 9’ W x 17’ L x 10’ H home brewery. I can do the math, so it looks like 400 CFA will work. I’m wondering if there are any adjustments needed based on WHAT you’re clearing. I see the comments above about cigar smoke, but what about steam? I’m going to evaporating (boiling off) about 2-3 gallons of water per hour, so aside from having the hood directly over the kettles, any adjustments to the math?
Howdy. I have a shop space, 50x50x14 and I have an exhaust fan that has a capacity of 7280 CFM with no static pressure interference. Can this fan pull enough CFM's to remove the hot air?
All i want to do is get some of the hot air from 92 degrees down to 80 degrees of my garage which is 19 x 19 x 7. I am going through a block wall .