Recommendations for a Range Hood Damper and Thermal Break
Looking at range hoods, it seems as though most manufacturers realize that their built-in dampers don’t work very well as many of the manuals contain text like:
Cold Weather Installations:
An additional back draft damper should be installed to minimize
backward cold air flow and a thermal break should be installed to
minimize conduction of outside temperatures as part of the vent
system. The damper should be on the cold air side of the thermal
break.
The break should be as close as possible to where the vent
system enters the heated portion of the house.
The question is, does anyone know of a good back draft damper that can be added that really does a good job of air sealing? Additionally, what do people use for a thermal break? I’m assuming some type of plastic fitting but I have not come across anything like that yet. Thanks.
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Replies
http://www.tamtech.com/Cape-Backdraft-Damper-6_p_17.html
http://www.fantech.net/RSK6Damper_enus-411114.aspx
Regarding thermal "break" - the most straightforward thing to do would be to insulate the entire length of duct...or at least the section up to and including the aftermarket damper and the outside wall. You'll still get a little bit of linear conduction through the duct, but it's really insignificant, except perhaps in CZ 7 and 8.
Nick and John,
I wouldn't use a Cape damper from Tamarack Technologies for this purpose. It's a fabric damper that will get gummed up very quickly with cooking grease if installed on a range hood exhaust duct.
The manufacturer notes that the owner should "Inspect, clean or replace [the Cape damper] annually" if it is installed in a range hood vent. I think that if you do much cooking, "annually" is optimistic -- it might need to be replaced twice a year.
I ended up using an American Aldes spring return damper on my range hood. It had slightly better spring action than the Fantech which, with our outside fan motor unit, seemed to stand a good chance of flipping open and sticking. Fantech damper was (up until a few weeks ago) repurposed for use as a make up air damper for the home; in that case the wimpy spring was desirable.
I also bought a Cape damper to examine, not sure I understand how that one really seals unless the wind is blowing against it.
I ended up sticking the Cape at the beginning of the duct that feeds combustion air to our masonry heater, mostly just because I had it. Gave me some security that there was no way I could ever get a "back puff". Two seasons in I now realize that is pretty much impossible given the stack effect in our home.
Nick,
Perhaps this is a side issue but I don't think it is the case that hood manufacturers realize their dampers don't work very well. Almost all exhaust fans are installed with the expectation that there will be an additional damper situated where the ducts exit the building enclosure.
Should the additional damper be a motorized one in a Passivehouse?
It's still not clear to me what a thermal break would consist of. They can't simply mean insulation as described above, or they would have said that.
Where do folks stand on this these days? Is a standard rooftop exhaust hood with damper + cheapo damper that comes with the range hood blower considered to produce fairly low leakage?