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To ERV or not to ERV?

Joe Norm | Posted in General Questions on

Hi All,

I am building a 1400 square foot home in the Pacific Northwest, doing most of the work, including mechanical myself. 

I am stuck on whether or not to install an ERV or stick to the exhaust only bath fan approach.

In a colder climate I think I would see an ERV as a no-brainer, but it’s late November now and I am still sleeping with a cracked window. The ocean influence keeps things pretty mild around here.

I really love the idea of supplying the house with fresh air, but I am wondering if going to all the trouble with the ductwork(no small task) and spending the money on a unit(probably $2K with ducts and registers) is worth it?

Or should I just keep using the window as a lower tech and much cheaper option? I will be heating with wood and a mini-split heat pump in the winter.

The house will be as tight as I can make it, but not a Passivhaus.

Thanks for your input and ideas

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  1. Jon R | | #1

    If cracking one window works, then so will a ductless (or nearly so) ERV/HRV.

  2. Expert Member
    Malcolm Taylor | | #2


    Why ERV not HRV in the damp PNW?

    1. Joe Norm | | #3


      Is an HRV a better choice around here. I was mainly going with an ERV because that is what the Intellibalance is.

      1. Expert Member
        Malcolm Taylor | | #4


        ERVs transfer both heat and moisture. That's great in cold climates where the indoor can get very dry, but here we battle high indoor humidity even in the winter.

        That said, I don't know if they transfer en0ugh moisture to make a big difference. Maybe someone with more knowledge can comment.

        1. Jon R | | #7

          On the other hand, if you are dehumidifying in the Summer, an ERV will reduce the amount of dehumidification required (as compared to an HRV).

          1. Expert Member
            Malcolm Taylor | | #8

            Most of the PNW is temperate enough that for the summer and shoulder seasons you can leave windows and doors open. I don't know anyone who de-humidifies in the summer, although maybe in large urban area they air-condition for a few weeks. Winter is where the problems come. My wife's heated but very infrequently occupied she-shed stays around 55% all winter.

  3. Expert Member
    Akos | | #5

    If you are in warm enough climate energy recovery might not make sense. Ventillation and tight houses is another story. Personally, before I got my ERV running, the house was always stuffy, opening the windows work but within a couple of hours of closing them the air was stale again.

    No matter which way you go, I would go with something that can ensure at least the minimum air changes per hour for you place especially in the bedrooms. Something that does not rely on the occupants to work.

    There are simulation tools out there (I use Hot2000) that you can put your house details into and see the energy costs for different ventilation and energy recovery strategies. I'm in a colder climate so here energy recovery makes a big difference.

    1. Jon R | | #10

      I don't see that HOT2000 has an ERV option. Is there anything in it that indicates if Winter indoor humidity will be too high or too low? The answer depends on various things, but would likely be high for 6 active people in a small house and low for 1 person in a large house. So favoring (in Winter) HRV and ERV respectively.

  4. Expert Member
    Michael Maines | | #6

    Joe, if you don't mind paying a bit more, the Minotair Pentacare system may be a good choice for you. It ventilates and modulates the humidity level to set levels, using a heat pump core instead of a counterflow core. It can also provide a bit of heating and cooling, and can control a Mitsubishi mini-split system for more control. I have not used one yet myself but intend to soon. The BuildEquinox CERV has some of the same functions.

    1. Joe Norm | | #9


      Looks interesting but might be getting a little complex for me. All I want to do is deliver fresh air to the house as simply as possible. I have never had humidity issues in my area.

      I am installing a a heat pump so that portion of it seems redundant.

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