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Community and Q&A

Kitchen vent fan cfm’s

swgold | Posted in Mechanicals on

I went crazy with my kitchen vent fan and installed a huge commercial kitchen vent. I love having it there in combo with our six burner range so it was in fact a good idea. Problem is , it sucks every bit of air out of the house and I would be scared to hold a small baby or puppy under the thing in fear of it being launched out of the house. In the middle of summer you can feel the temperature rise in the house. It is probably about 6-700 cfm. Here is the problem: I only had room for a 6″ line under the oven for a makeup air vent. I have a radiant floor so that was as much room as I could get between coils (afterthought). And I could only get one hole there due to other obstructions. I bought a “530 cfm” in line fan that is almost pulling enough air, but not quite. I got the 6-700 cfm from a company that did a pressure test on my house, so I took a wild guess on buying the inline fan hoping I might have to dial it back with a motor control. They read 500 or so cfm’s coming out of the vent, but it was not a tight fit so I am not sure exactly what the real number might be. At any rate, what would happen if I bought a bigger in line vent fan and reduced it to 6″? Would I gain anything at all? The inline fan is only about a two foot run under the house to the floor under the stove. I could not find a 6″ in line fan that was any more powerful than 530 cfm. I know I could damper the vent fan, but I would rather not. We do a lot of smokey cooking and it is something that I would really like to make work. And the vent fan is 220V and would require a pretty expensive VFD if I wanted to control the speed.

Hope this is not too much for this forum,

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  1. GBA Editor
    Martin Holladay | | #1

    It sounds like you have painted yourself into a corner by installing a large exhaust fan -- one that requires a powered makeup air system -- without planning ahead. (The requirement for a powered makeup air system is a code requirement in most areas. Any contractor installing a large range hood fan should understand the code, but many don't.)

    Here is a link to an article that provides more information: Makeup Air for Range Hoods.

    You have several options. One option is to remove your existing range hood and install a range hood with a smaller exhaust fan.

    Another option is to find an HVAC contractor who knows how to install a properly sized makeup air system. The makeup air needs to be introduced into your house, but does not necessarily need to be introduced into your kitchen. In some cases, it is easier to introduce the makeup air into a different room of the house.

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