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  1. #1
    Join Date
    Apr 2011
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    Can Anyone Explain The Pros & Cons of a Passive HRV?

    Hi Everyone,

    Thanks for taking my question.

    I read this thread
    and Carnak and others had a great discussion of passive HRVs.

    However, in the end, I still feel like the case has not conclusively been made on passive HRVs.

    I'm wondering if you can lay it out simply for me:

    I am gutting my house in Winnipeg (6387*C or 11496.6*F HDD) and basically bringing it up to R-2000 standards. (R60 roof, R-24 walls via cellulose & XPS.)

    What would be inferior about a passive HRV? My idea is to plumb it so the bathroom and other exhausts go to the HRV core and exhaust from the building. Then, incoming air passes through a motorized damper activated by a combination timer / humidistat and interlocked with the bathroom/exhaust fans and the furnace motor on low speed. Fresh air goes to the furnace supply air. Essentially, the house would only draw air in volume when the exhaust fan was on, but it could allow some air to come in if the exhaust fan was off.
    Does this work? It seems this would eliminate the need for expensive extra ducting and extra motors, plus I can take advantage of the ECM motor in my furnace.

    If required, We could put some motorized dampers to recirculate furnace air through the HRV if it frosts, but it seems that the Hoyme unit is not succeptible to frosting because it has large diameter tubes.

    Here is a Nu-Air Passive HRV. Maybe it is a bit different than the Hoyme that was being discussed:
    Nu-Air Passive HRV - NU120 and NU120-MD (Motorized Damper)

    Hoyme HAE - Motorless Air Exchanger:


    Thanks for your time,

  2. #2
    Join Date
    Oct 2009
    Los Angeles
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    My understanding is that the fan in an efficient HRV uses much less electricity than the fan in a typical air handler. If you are gutting the house, the most effective ventilation system will use it own ductwork designed for continuous, low volume airflow, while the heating system uses larger ductwork designed for larger heating loads. The passive system will be cheaper upfront, but will use 500-1000 kWh a year more in electricity.

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