ERV installation options?
I will try to keep this succinct – I purchased a home in SW Montana last year that was built in 2013, climate zone 6. During winter we see temperatures -20F and colder quite often. I’ve been on a journey learning more about construction techniques, building science and now ventilation.
It’s a 2100sqft 3bed/2bath home, standard framed construction over encapsulated crawlspace outfitted with a common ArmstrongAir A95UH furnace and rigid trunk & branch duct system (none of the takeoffs is flex, all rigid duct).
The attic is insulated with blown-in insulation on the ceiling, the roof is vented judging by the vents in the soffits outside.
I’m getting a blower door test performed soon but I imagine it’s constructed reasonably airtight. I’ve been looking at installing an ERV system to improve indoor air quality, as you can imagine, there aren’t many opportunities to open windows. RH stays very low, 18 – 32% – the forced air heating keeps it very low.
First option: the go-to method for all contractors I spoke to so far is to use the existing ducting and connect into the return air. I’m not excited about this method because:
Second option: installing dedicated ducts in the attic. This seems like a non-starter to me to have ducts with heated air go through/on the edge of the thermal envelope as the attic is not conditioned (9F – 25F over the past week).
Third option: second dedicated trunk & branch duct system in the crawl space just for ERV? I have no idea how viable this is? Is there space? Will it be cost prohibitive?
Are there any other ideas? Surely this must come up a lot of retrofits?
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