ERV intake and exhaust through eaves
I’m installing an ERV in our attic while converting to a conditioned attic with R20 foam above deck and R21 dense pack cellulose in rafter bays, zone 4c.
My original thought was to place the intake on the gable end, and the exhaust through the roof as there isn’t room for it an appropriate distance from the intake. ERV will normally run around 60cfm with up to ~200cfm boost.
However I’m now considering doing both through the eaves on opposite sides. We have sloped open eaves with 2×6 rafters. I would transition the 6″ round duct to 8″ oval (3″ x 10.5″) and terminate at the rafter blocking above the top plate. We have 2ft overhangs.
Any downside to venting at the eaves? It would avoid a roof penetration and a very exposed gable intake.
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Replies
Peter,
The intake is fine, but you don't want to exhaust warm, moist interior air onto the underside of your roof overhangs where it may cause rot.
Thanks, I suspected I was missing something!
We are exhausting the baths through the ERV so that puts a point on it.
I can exhaust through the gable end to avoid the roof penetration although this places a vent on the front of the house.
The beauty of an ERV is that it is exchanging heat and moisture with the outside air as it is exhausted. This generally means the air coming out of the ERV will be near outside air temperature and humidity.
In the winter it will be slightly warmer and more moist but not a enough to matter if you have a high efficiency unit. You can vent into the soffit area, I would make sure the soffit roof vent intakes near it are blocked off. Sample of one, mine is vented under a 2' deep steep overhang and has been fine.
FYI Broan has a combination intake/exhaust ERV vent hood assembly that might be something you could use; I use it with their ERV that has a maximum flow of 135 CFM, although I don't know if that's the limit of the hood assembly.
If it's this one the max is 110 cfm. https://www.sylvane.com/broan-tandem-transition-kit-vtyik1.html?gad_source=1&gclid=CjwKCAjw4ri0BhAvEiwA8oo6F5tt0NUurRTzrFqU1jTiAlMB27oUlHk_KUQsqa9hwk3BGPUzsWNTYBoClWwQAvD_BwE