# CFM reducer for residential hoods



## Sifu (Apr 29, 2013)

http://faberonline.com/specsheets/cfmspec.pdf

Anybody used this to reduce the cfm down in residential?  Finding lots of 600-700 cfm fans installed and have been asked if this is an acceptable alternative to make-up air.  I have never seen one?  Any thoughts?


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## mjesse (Apr 29, 2013)

Curious as to what this does to the warranty of the hood?

I would think the increased back pressure would not be recommended by the mfr. Fan works harder, burns out...

Also, what happens down the road when the hood gets changed out? Will new owner/installer know there is a "restrictor plate" installed?

I vote no, unless approved by the hood mfr.

mj


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## Gregg Harris (Apr 29, 2013)

As stated by mjese. terrible idea, the static pressure created will cause premature fan failure and the cross plates will collect grease.

I say no


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## klarenbeek (Apr 29, 2013)

I would say no also. There's a reason most hood manufacturer's have minimum duct size right in the installation instructions. Also, at least in our jurisdiction, we go straight of the nameplate rating for residential hood cfm.  If the nameplate rating is over 400cfm, makeup air required.


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## klarenbeek (Apr 29, 2013)

BTW, if they want to reduce the cfm, why not just go with a smaller hood to begin with?


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## Sifu (Apr 30, 2013)

You are all echoing my thought.  My first concern was about the back-pressure from the fan.  I like the term "restrictor plate" as well.  My objection to the BO was that you can restrict the air coming out of the other side of the restriction but they will still be trying to force in air on the intake side.  What I am seeing is a bunch of 600 to 700 cfm hoods.  My recommendation will be to not permit it.  Provide make up air.

Thanks to all.  I really appreciate this forum.


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## Sifu (May 1, 2013)

Quick update, the "restrictor plate" came from the same manufacturer.  The hood requires a 6" duct, this would reduce that.  I told them if they get a letter stating it is acceptable to reduce the duct, won't harm the listing and that the back pressure isn't an issue for the fan or for the effect on the room we could revisit the option.


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## electriclese (Jun 6, 2013)

Can u use a speed control?  (Does manufactirer allow it?)  Just tossing out ideas.


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## Sifu (Jun 6, 2013)

That is one solution that would provide relief but the code states that a system capable of exhausting in excess of 400cfm.  So unless a permanent speed control were put on it wouldn't meet the code.  I did receive a letter back from the mfr but it left a little to be desired.  It has been decided to not allow the restrictor plate for the reasons mentioned in previous posts.   Several more have been found since the first post and most say they will simply change out the units after finding that the options for altering them are either too prohibitive or would violate the listings.  Word has quickly spread and most are paying closer attention to the cfm on the fans they are installing now.


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## rleibowitz (Jun 6, 2013)

It would helpful for those of us in cyber-land to get the code section along with the quote. I have never heard of the 400cfm rule and would like to look it up and read it for myself.


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## rleibowitz (Jun 6, 2013)

Thanks anyway found it at 2009 IRC M1503.4


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