What’s the best kind of damper to install on a kitchen exhaust fan?
Luckily, my clients trust me and declined to order a huge 1600 CFM kitchen exhaust fan, and settled on a 3 stage fan with a maximum of 400 CFM. I’d like to install a damper somewhere, but I’m running into two issues: First, it seems that building code here in NJ does not allow for an inline damper to be installed (I think). I searched for wall termination louver type dampers, but this fan is not powerful enough to open them (they are typically used in commercial or industrial applications). Secondly, I can’t use the typical cape type dampers because I’m concerned with kitchen grease building up.
So what are my options? No damper? A flimsy wall termination damper that doesn’t do much to prevent air from leaking into the home? What do the Pros at GBA usually do?
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Range manufacturers should tell you the kitchen exhaust fan size required for the range your client selected; you can’t arbitrarily reduce that size. If the size of the exhaust fan is over 400 cfm, you must provide independent make-up air for it (see 2009 IRC M1503.4). Broam has a mechanized MUA damper that is synchronized with the exhaust fan.
Martin Holladay wrote a good article here at the GBA. See: https://www.greenbuildingadvisor.com/blogs/dept/musings/makeup-air-range-hoods
Related to this question, can anyone comment on the idea in general of installing a backdraft damper in your kitchen hood exhaust duct? We have a pretty normal (200-300 CFM, IRRC) kitchen hood. With the airsealing I have done, it is now the biggest uncontrolled opening to the outdoors. We're not worried about total ACH - it's a 100 year old house and while it's pretty tight it's got enough small leaks that we won't need active ventilation. So I'd like to cap this big hole in the envelope, but I'm worried about installing a backdraft damper due to the potential for grease buildup.
Can anyone comment on this issue? Am I worried about nothing? (This is, after all, a residential kitchen, not a commercial one.) If this is a legit concern, is there a particular kind of damper I can look for which will be OK in this context? Is putting a backdraft damper in a kitchen exhaust just a bad idea no matter what?
Plenty of manufacturers make backdraft dampers for range hood exhaust fans. Here's one: