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Community and Q&A

Choosing an ERV

Alan Afsari | Posted in Mechanicals on

– I am trying to choose an ERV for our home build
– Climate zone 5
– 4300sq foot ranch on conditioned crawl
– The Heating and cooling plan is to use ducted minisplits
– There are 4 bedrooms – 5 people.  There are 4 bathrooms with showers.  One powder room.
– I calculated our ventilation rate should be 167cfm. 
– The ERV will have dedicated ducts.

I like the idea of demand-controlled ventilation based on CO2 monitoring and possibly VOC monitoring, but I think that is only available with CERV, Ultimateair, and Zehnder.

1- When selecting the unit, how much higher capacity should the rate be for increased demands (showers, bathroom use, parties) 40 or 50cfm over the calculated rate?
2- What are people’s opinions of these units?

Venmar           X24ERV ECM – up 210 cfm – SRE 84% at 0degC

Ultimateair      200DX – 30-200cfm – SRE 83% at 0degC (with active defrost below 12degF)

Renewaire       EV200 – 100-200cfm – SRE 78% at 0degC

3- Any maintenance issues that owners of these units may share (positive and negative)
4- How loud are these?
5- Any better suggestions?
6- Should I consider a CERV2 or Minotair?

Thanks in advance.

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  1. GBA Editor
    Brian Pontolilo | | #1

    Hi Alan,

    I can't speak from experience about any of these units, I can only say that I have heard a lot of good things about the CERV equipment. Hopefully some GBA members will see your post soon and share their experiences.

  2. Jon R | | #2

    Self balancing will have some positive effect on efficiency.

    Not answering your question, but also review your ducting plan. I'd supply 20 CFM/person of outside air to closed door rooms (for CO2 reasons).

    A simple solution to not providing 40 CFM to a bedroom when it isn't occupied is to use a separate spot ERV and manually turn it on as needed. Or open/close dampers and adjust the central ERV fan.

    I'd use an exhaust fan for bathrooms.

  3. Alan Afsari | | #3

    Any input from others/GBA pro's would be greatly appreciated.


  4. Expert Member
    Rick Evans | | #4


    There is an ongoing debate about how much ventilation is actually needed. Martin has written excellent articles on this.

    It sounds like you are using the newer ASHRAE standard for calculating ventilation rates. Many building scientist believe those rates are way too high. I am personally inclined to agree with them based upon my own experience with my ERV.

    The Building Science Corp calculation for ventilation is closer to 80 cfm/minute, nearly half the rate you stated above.

    Anyway, I've experimented with the CERV a few times and really like it. It de-humidifies incoming air in the summer and also cools it. In the winter, it can warm the air. It doesn't run continuously, only when needed. My only complaint is that it works more like an HRV in the winter in that it seems to dehumidify the already dry air. This may not be an issue in a house with 5 people- especially if you happen cook a lot, water plants, and take long showers.

    I have the Panasonic ERV and really like it. It's simple, inexpensive, and easy to install. It doesn't have a "boost mode" but I've heard anecdotal accounts boost mode doesn't work very well anyway.

  5. Alan Afsari | | #5

    I hired an engineer/designer to design the duct system, calculate heating and cooling loads, etc. He is sort of leaving selection of the ERV to me.

    I like the idea of demand ventilation something like CO2 monitoring...

    I think I like the Ultimateair ERV - allows for demand ventilation. It seems to have the highest filtration which is attractive (our heat index is 108deg with poor air quality in Detroit today - make filtration seem more important). Variable speed motor -- maybe be higher filtration is worth the higher energy costs?

    If the CERV is more like an HRV in the winter - that is probably not good for us. Our current home is dry in the winter - it would be nice to keep winter humidity levels more comfortable (w/o a humidifier) -- hoping our 'tight' new home will be the biggest improvement for that -- ERV makes more sense to recover the indoor humidity.

    Thanks for the responses.

    More responses would be welcome.


  6. Eric Whetzel | | #6

    This probably doesn't help Alan at this point... but overall we've been happy with our Zehnder ERV. We definitely like the 'boost' function. We don't have any mold or mildew issues in our bathrooms, and even with a recirculating range hood, we've avoided any lingering smells from cooking.

    The Zehnder is typically the most expensive unit, but we felt like we were able to balance out the cost by installing their 3" ComfoTube ductwork ourselves.

    We've been impressed (shocked?) with how much 'stuff' the MERV 13 filter for incoming fresh air captures. The filter is mostly black and needs changing every month or two.

    Using the CERV or Minotair is not risk free. What happens should they go out of business, or if they have poor customer service? If it's a catastrophic issue/failure, can you afford to replace the unit with an entirely new system (typically 3 stand alone units --- heat/AC, ventilation, dehumidification)?

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