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Our indoor humidity is 65-70% consistently, dips to mid 40s in the winter. Why so high?

user-973468 | Posted in General Questions on

I’ve got an indoor humidity question. The house is about a year old, 1700 s.f. with a final blower door of 90 cfm50. We’ve got a Venmar Eko1.5 ERV and minisplits.

Outside humidity doesn’t seem to matter, inside humidity remains fairly high. Our indoor humidity is 65-70% consistently, dips to mid 40s in the winter. There’s none of the obvious moisture makers and no sign of leaks. It’s almost like the ERV “multiplies” the moisture. My original understanding of the ERV was it was going to help lower the humidity? Any Ideas would be appreciated.

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  1. GBA Editor
    Martin Holladay | | #1

    Running your ventilation system in the winter will lower your indoor relative humidity (RH). An HRV does a better job of lowering your indoor RH than an ERV (because an ERV transfers some of the humidity from your exhaust air stream to your incoming air stream).

    During the summer, on the other hand, running your ventilation system almost always makes your indoor RH worse -- that is, it raises the indoor RH -- especially in a humid climate. If you are worried about high indoor RH, you want to run your ventilation system as little as possible during the summer.

    For more information on these issues, see HRV or ERV?

  2. Expert Member
    Dana Dorsett | | #2

    90cfm/50!?! That's something like a WORLD RECORD level of air-tightness (and hard to really validate!)

    ERVs only exchange about half the moisture, and as Martin correctly points out, running a high ventilation rate with an ERV still delivers a very significant latent load in much of the eastern half of the continent (albeit much more in Alabama than in Ontario). Unles there is a sensible load to match, the mini-splits won't be running hard enough to pull that moisture back out. So the first step, minimize the ventilation rate on the ERV whenever the outdoor dew points are above 55F (which is nearly 100% of the summer, in my MA location.) If that still isn't doing it, run a standalone dehumidifier.

    For high-R homes with minimal sensible cooling loads and using mini-splits for both heating & cooling it's useful to use a Daikin Quaternity as the main mini-split, since it can dehumidify at high efficiency in either heating or cooling mode, even without changing the room temp. (The temperature and humidity setpoints are set independently.) A 1-ton Quaternity still might not keep up with a very-high ventilation rate from the ERV though.

  3. kevin_in_denver | | #3

    In my experience with cheap humidity monitors, they read about 15-20% higher than the actual humidity, regardless of brand.

  4. kevin_in_denver | | #4

    And that's just a guess by calibrating with a cheap honeywell humidistat.

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