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How necessary is ERV for residence?

Right-o on my setup.

The first question you have to ask yourself is, how tight is your envelope? Insulation notwithstanding, how much infiltration do you have? If it is sealed enough that a blower door test reveals less than 0.50 ACH per hour, you may have a need. More than that is a "want", unless your exhaust hours of operation are most of the day. Typically an ERV or HRV is sized for about 0.35 ACH to give you an idea of the scale of things. If your ACH is above 0.50 by a good deal and unless there is another parallel need (as in my case) it is a "want".

As to HRV or an ERV, here is the scoop: How many hours of heating and how many of central cooling, coupled with how many hours of below-freezing weather do you have? Each ERV manufacturer uses a different technology.

The best ERV's (Energy Recovery Ventilator) is a 4 angstrom molecular sieve type. These can be coated paper or plastic cores or made of a solid desiccant material. These recover both sensible and latent heat. If you humidify in winter and dehumidify in summer, this is the way to go.

Typically, the colder the climate the more likely it is that you will go to an HRV (Heat Recovery Ventilator) which is sensible-recovery only. South of the Mason-Dixon line, ERV's are more common. In the Yukon, HRV's rule.

In my case it was a matter of recovering what little heat the bathroom exhaust would lose coupled with the need to supply OA to the interior laundry room for combustion air. The hours of operation say that the 70% efficient unit would be just fine.

I just specified three (3) 95% double-core HRV's for a school to ventilate interior corridors that never had ventilation (since 1956!). The HRV's made far more sense as there is no cooling.


  • D107
    D107 Member Posts: 1,849
    House envelope gradually getting tightened

    Assuming an old house envelope with blown-in cellulose, Icynened attic, weatherstripped doors, doublepain vinyl windows etc. and 3-ton AC in attic to which ERV or HRV would be connected.

    I ask because in watching the ASHRAE live conference the other week, great emphasis was put on dehumidifying incoming air. Last year Brad posted that in his place he had an HRV: a Lifebreath 200 (70% efficiency) exhausting bathroom and imparting OA to the laundry room. Manual twist timer in bathroom and Veris Hawkeye current transformer when drier is on.

    Don't know price difference between HRV and ERV for my setup; I know that the Conference was probably largely focusing on commercial buildings. In the NY area--wet in summer, dry in winter--it doesn't seem like a bad idea to humidify or dehumidify OA, warm incoming frigid air in winter, and have some kind of filter on the incoming.
    Is this overkill?
  • D107
    D107 Member Posts: 1,849
    Less memory than a good email and bookmark archive

    If Dan ever pulled the bookmarks, US hydronics would be in deep trouble...

    So me being 30 miles above nyc and you in MA, you might be slightly colder. (I'd say average annual degree days up here is 5500, though 2006 was only 5000.) So if it wasn't for your laundry room OA requirement you might not have bothered. I think at best my eventually sealed house will be .3 or .2 ACH; I assume you've done at least that well so, perhaps, given your profession and attention to detail, I need not be so concerned.

    It does seem strange to me that even in the Yukon, they would not humidify (and even slightly heat) the incoming very dry air.


  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    Always a pleasure

    Always a pleasure reading Brad's posts...

    You should have kept your bookmark a secret, as I was very impressed with your recollection skills.

    Thanks again Brad for your insight.
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