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ERV vs. HRV: humidity reduction

rodrob15 | Posted in General Questions on

Hello All,
 
Can anyone reference any case studies that have been done that compare the performance of an HRV to an ERV in the same home? Specifically, I’m looking for data that compares what each unit does to humidity levels in the same house/environment.  Theoretically, I’m thinking that an HRV should lower humidity levels more than an ERV since an HRV introduces dry air to a home and an ERV does not. Or perhaps the overall difference in humidity reduction is fairly negligible even though an HRV is introducing drier air?  

Long-story short, I’m getting ready to install a fresh air system in my new construction home and an ERV would be preferable given I wouldn’t have to install a condensate line, which would require a condensate pump in my situation. I did construct a very tight home and do have a little bit of a moisture problem when there’s no ventilation (generally 50 – 60% relative humidity). However, if its been shown that an HRV reduces humidity levels considerably more than ERV, I’ll probably go that route since getting the humidity level below 50% is the most important goal. 

Here’s some additional details about my home:
– 1,700 sqft new construction home.
– Fresh Air system has dedicated ducts, but is not a perfect design given constraints from beams, etc. I have stale air that is pulled from each bathroom and fresh air that is delivered to 2 out of 3 bedrooms and 1 out of 2 living areas
– West Virginia Location, Zone 5 Climate

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Replies

  1. Expert Member
    Akos | | #1

    Colder climate but do show what happens when you go from HRV to ERV core. Surprisingly not much.

    http://www.solaripedia.com/files/1287.pdf

  2. Jon R | | #2

    You don't need a study since the effect can be more accurately calculated. But you do need to know the conditions - outdoor dew point, amount of source moisture, amount of ventilation air, leakage air, HRV/ERV specs, etc. Short answer - in a well ventilated but tight house there will be a significant difference.

    1. Expert Member
      Akos | | #3

      Actually it is not that straight forward. In cold climate, when the HRV goes into defrost, a fair bit of the condensate gets re-evaporated and cycled back to the room. Overall an HRV should dry the air more, just how much is not easy to quantify.

  3. John Clark | | #4

    Answer: Dedicated dehumidifier

    Depending on ones climate zone an ERV and HRV can address humidity but at different times of the year and under certain conditions. This is why, generally speaking, in you don't want to rely on either to act as a dehumidifier when you experience high levels of humidity at some point during the year.

    1. Jon R | | #5

      Agreed, but you can't use normal dehumidifiers to bring Winter humidity down to a safe 30%. Which leaves you with reducing sources of moisture, HRV or exhaust only (which some HRVs do to avoid defrost).

      1. John Clark | | #6

        Yep. There are so many variables that we can't unequivocally say one or the other. It just depends on the climate zone and occupant behavior. For the OP in CZ 5 a dedicated dehumidifier probably going to be required during the summer months and perhaps the shoulder season regardless of whether an HRV or ERV is chosen.

        If the OP has a lot of indoor water usage (i.e. occupants of 3 or more, plants) than a HRV might be a better option OR just getting rid of the plants.

        1. Jon R | | #7

          Yes, lots of sources say use an ERV or use an HRV based on climate. But it's easy to calculate that in the same cold climate, one house/occupants/activities will be too humid in Winter (suggesting a HRV) and that another will be too dry (suggesting an ERV). Reports on GBA seem to support it going either way.

          Most important point - don't let 50-60% occur in cold weather. It is likely to be very damaging.

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