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ERV for One Floor vs. Whole House

pjpfeiff | Posted in General Questions on

Does an ERV make sense for one air-tight level when the other levels are leaky?

I have a 1950s Cape Cod and am renovating the 2nd story (previously-unfinished).  Let’s assume I’ve done a good job with that and the 2nd story is now good on air-tightness, but the basement and 1st story are not.  My questions are:

(1) Does it make sense to add an ERV to the 2nd story only?
(2) Does it make sense to add an ERV to serve both the 1st and 2nd story?

I *think* the answers are “yes” and “no” respectively, but would appreciate others’ insights.

Agree or disagree with the following:
By my reckoning, an ERV changes nothing about the airflow through leaks in the house.  So to have an ERV serve the 1st story would be to pay its energy penalty without any real gain.  The air might become slightly cleaner by virtue of dilution (adding a clean air stream on top of the leaky/dirty one), but that is all.  The 2nd story, on the other hand, has no leaks to provide air, nor will it get air from the lower levels without a significant temperature differential.  So something like the Panasonic WhisperComfort ERV could be useful.  However…it’s not that efficient and I don’t like its aesthetics, so I might just use the bathroom fan to pull in air of the same quality that already exists downstairs.

I suppose question (3) is, how confident should I be about the air-tightness of the 2nd story?  Unless I were to air-seal between stories (which I have no intention of doing) then I don’t see a way to, say, blower-door test just the 2nd story.  The entire enclosure had flash-and-batt, and it got new windows, so it seems like it ought to be good.

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Replies

  1. Jamie_Givens | | #1

    I’m doing a similar thing now…did you ever come to a conclusion?

  2. pjpfeiff | | #2

    I decided just to ventilate the upstairs with a pair of Lunos e2s. The air quality up there improved noticeably (by subjective measures) when I got those in service. In fact it was noticeable enough that now I am seriously considering adding balanced ventilation to the rest of the house, if I can find a reasonable way to do it. Additionally, I have since purchased a CO2 monitor and found that levels in our bedrooms (on the first floor) get high overnight. There are probably easier ways to address that than an ERV, but I still take it as evidence that an ERV on the (presumably) leaky first floor could be beneficial.

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