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Community and Q&A

HRV/ERV vs exhaust only issue…

QTrKnzPUgL | Posted in Mechanicals on

I’m looking for some advice on ventilation. I live in VT in a house I built in 1997– 1800 sqft, fairly well insulated, tight but not super-tight, main heat source is woodfired thermal mass heater. Open floor plans. Ac/H were estimated (not tested) at .5 at the time of construction.

When I built the house I installed ducting for an HRV (exhausts from upstairs and downstairs bathrooms, two returns on each floor.) However as the house seemed far less tight than I expected, I never installed the actual HRV unit. As a result there was no bathroom ventilation. This has never been an issue until the last couple of years when we have had long periods of very high natural humidity, even into the winter. I have seen some mildew developing in the downstairs bathroom over this time. As I am renovating that bathroom (for other reasons) I thought it was time to finally get the ventilation installed.

I’m wondering whether it is worth putting in an HRV or ERV as opposed to an exhaust fan. Because of the layout of the house and existing ducting, the easiest way to install an exhaust only unit would be to put a remote fan in the basement controlled from each bathroom. I do have some concern with not creating a backdraft on my thermal mass heater running an exhaust only unit.

In looking at HRV/ERV units, some manufacturers seem to discourage taking exhaust air from bathrooms, while others recommend it. I was looking at these American Aldes units:

However I am not sure if an ERV or HRV would make more sense in my situation. Also I noticed looking through some of the threads on this forum that this manufacturer isn’t mentioned very often… wondering if their products have problems. I also have looked at the RecupAerator as well, which is slightly more expensive, and they seem to discourage exhausting from bathrooms.

Thanks in advance for any advice on this matter!

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  1. wjrobinson | | #1

    HRV is best in our area. ERVs transfer moisture.

    I would try just an exhaust fan and just run it during your showers and for twenty minutes after if your home is not too air tight like you state.

    To be more safe, get your home blower door tested and have an HRV installed via a few bid requests.

  2. GBA Editor
    Martin Holladay | | #2

    Since an exhaust fan costs much less than an ERV or HRV, you might want to start with one or two exhaust fans and see if an exhaust fan meets your needs.

    Since the rate of air flow through a bathroom exhaust fan is relatively low (30 cfm to 80 cfm), it should not cause a combustion appliance to backdraft.

    If you end up installing an ERV or HRV, but don't know which one to choose, you might want to read HRV or ERV?

  3. user-1005777 | | #3

    I had a similar problem in one bathroom. There was an exhaust to an air exchanger in the bathroom, but the dehumidistat was in the living room. The air exchanger was too expensive to run, so i blocked off the outside supply duct and the supply to the house. I moved the dehumidistat to the bathroom, just above the shower curtain rod. That worked fine, but after we sealed up the house we were not getting enough fresh air, so we installed an HRV that runs 15 minutes every hour during the day. Voila! No mold problem and lots of fresh air.

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