GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Zehnder HRV/ERV configuration

syadasti | Posted in Mechanicals on

We got a quote on a HRV/ERV 550 model, we had been trying to decide whether to size down to a 350 or not but I think we’re going to stick with the 550 they recommended.

We were specced an electric in-line heater ($699) for it but my architect suggested we also consider the geothermal PEX ground loop product ($2000) they offer in the foundation to save energy at pricing delta of $1300 more than the electric resistance heater. I am not sure what the total power saving is or reliability between the two, but I do know that PV systems run around $3/W before the tax credit so they ultimately go for around $2/W installed – for the equipment pricing difference we could add two solar panels to our array around 650-700 W of capacity and have a simpler and more reliable in-line electric heater for the air rather than the geothermal pex system.

There’s significantly much less labor to install the in-line heater and the geothermal requires an expert in geothermal for installation and more maintenance for the brine lines etc – a good contractor is essential (anyone recommended in the VT area?). The labor difference we’d probably have another 350-700W of PV installed so maybe 1.4 Kw PV array providing benefits for the whole year.

Heater is 3.5 Kw micropulse on demand based on temperature (25F HRV or less 14F or less ERV) and ventilation rate. Geothermal 5-70 W in operation and runs all the time rather than micropulse. Heating degree days would affect value, this project is in North Central VT in the mountains. Also geothermal product takes moisture out in the summer but the heater does nothing then – two solar panels would generate electricity year round (a lot more in the summer)

What way should we go and why – I’m not so certain but maybe the simpler setup with 2-4 extra PV panels for the $1300 equipment cost and additional labor is the best use of our money?

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. GBA Editor
    Martin Holladay | | #1

    Here is a link to an article that addresses your questions: Using a Glycol Ground Loop to Condition Ventilation Air.

  2. this_page_left_blank | | #2

    It's debatable whether the total cost of the ground loop makes sense even if you're paying standard rates for electricity. So if it's a choice between PV and the ground loop, the PV almost certainly wins. UltimateAir's ground loop system is significantly cheaper than Zehnder's. I'm in a position where I already have the pipes buried, and even at that I am struggling to justify completing the system. I think the only way it makes economic sense is a DIY custom solution. You can get a liquid to air heat exchanger, circulator pump and temperature controller for about $200 total. I don't think you need an expert in geothermal for installation. I'm curious, what is the square footage of the house and what method was used to determine the CFM requirement?

  3. syadasti | | #3

    Thanks do you think the Zehnder with electric resistance is best with money left over for a larger PV or I should look at the Renewaire ERVs plus money towards the PV array?

  4. syadasti | | #4

    We had planned to use the Zehnder with an HRV core for a few years and then switch to an ERV core, should we consider just using a Renewaire ERV from the start and forget about this resistance heater energy use?

  5. syadasti | | #5

    3046 sq ft

    Upper Floor 1,000
    Master Bath 2 20 TVA 2T STB-1
    Kids Bath 2 20 TVA 2T STB-1
    Master Bedroom 3 30 TVA 2T KE
    Kid's Bedroom #1 2 20 TVA 2T KE
    Kid's Bedroom #2 2 20 TVA 2T KE

    Ground Floor 1,078
    Kitchen 3 30 TVA 2T STB-2
    Powder 1 10 TVA 2T STB-1
    Mudroom 1 10 TVA 2T STB-1
    Laundry 1 10 TVA 2T STB-1
    Conservatory 1 10 TVA 2T STB-1
    Living 2 20 TVA 2T KE
    Dining 2 20 TVA 2T KE

    Basement 968
    Guest Bath 2 20 TVA 2T STB-1
    Mechanical 1 10 TVA 2T STB-1
    Guest Bedroom 1 10 TVA 2T KE
    Play Area 1 10 TVA 2T KE
    Storage 1 10 TVA 2T KE

    Total 3,046 24,977 28 140 140
    Air Changes/Hour: 0.34 Est. Ave. Duct Run: 40 ft.
    Est. Ave. Ceiling Ht.: 8.2 ft.

  6. this_page_left_blank | | #6

    The Zehnder electric heater seems very expensive, for what it is. Other brands are less than half that amount.I don't know what the pricing is like on the Renewaire, but it doesn't really compare to the Zehnder in efficiency specs. I would say it doesn't make much sense to get an HRV core only to upgrade it later to an ERV. If ERV is what you want or need, just get it. Are you saying that with an ERV you won't need pre-conditioning? If that's the case, definitely skip both the heater and the ground loop.

  7. syadasti | | #7

    The article that Martin linked to suggested that:

    "some energy consultants are taking a second look as simpler solutions — for example,
    specifying a $1,000 ERV from Renewaire. (Renewaire ERVs have no condensate drain. Because moisture is transferred across the unit's permeable ERV core, these units don't need to be periodically defrosted.)"

  8. syadasti | | #8

    The Zehnder 550 runs at 350W at 324 cfm. The Renewaire 450IN EC runs at 315 W at 350 CFM, not sure what the heat recovery is for that unit but the smaller EV300 is maybe 10% less than the Zehnder but doesn't need a preheater for temperatures lower than 14F.

  9. syadasti | | #9

    Going with the Zehnder 550 with the in-line heater, seems worth the premium compared to anything else.

  10. lance_p | | #10

    From what I've seen, Zehnder does not publish full data allowing comparison to competing products.

    I have not looked at all of their products, but the Comfoair 200 is advertised at 92% efficiency. 92% will surely represent the efficiency when the unit is at its lowest airflow rate, and it is my personal belief that Zehnder develops their products with a very low minimum airflow rate just so they can advertise that high "peak" efficiency, reported as "up to" 92%. The unit goes from 29 CFM to 118 CFM, an incredibly wide 4x range, much wider than other products I've looked into which typically vary only by 2x or not at all.

    Zehnder spends far more effort characterizing the noise output spectrum of the unit, an area where it curiously does not meet PHI standards, than characterizing the thermal efficiency of the unit. They also do not publish data for the ERV variants of their exchangers, so I'm not sure how they compare to their HRVs.

    J M, why are you looking at a 324 CFM exchanger? A 3000 sqft house with 4 bedrooms only needs 67.5 CFM of continuous air flow to meet ASHRAE 2010 standards, and only 127.5 CFM to meet the newer 2013 standards (which are seen by many experts as excessive).

  11. syadasti | | #11

    Zehnder had recommended the 550 but my architect who's own personal house that's about 500 sq ft smaller had too thought we probably didn't need it a majority of the time. He has a 350.

    We aren't going to have bath fans in this house but we will probably have outside venting kitchen hood as we do cook a lot (it will be all electric cooking appliances) but this will have an electric damper and only be used when there's lots of cooking and/or something is burning.

    The ERV wall controllers in the kitchen/bathroom with the boost mode are when we'd want more airflow but otherwise the 350 is probably fine vs the 550.

    It seems like the Zehnder, Ultimate Air, or new Broan/VanEE ECM ERVs could all be very good options. AFAIK only the Zehnder and Ultimate Air have a summer night bypass mode for bringing air in from the outside when it's cooler outside, right?

    Low noise operation is very important to us too and I assume Zehnder's duct work system helps a lot in transmitting noise too.

    Do you think there's a good reason to consider other options besides the 550? I've never lived with any of these ERVs.

  12. lance_p | | #12

    The bypass mode could be a reason for wanting a higher flow unit. Good point, and many ventilators do not have that feature, though I've also read that the effectiveness of the bypass mode is often overstated.

    I don't question that Zehnder makes a high quality product, but they command quite a premium over other products. Noise seems to be an issue with many ventilators, though installing a few feet of insulated flex duct between the unit and any hard ductwork makes a big difference.

    If Zehnder has given you a quote I would consider the cost and get estimates from other companies/contractors and go from there. Many other companies make high efficiency recovery ventilators.

  13. STEPHEN SHEEHY | | #13

    JM: Why do you need the inline heater at all? We're in Maine. Our HRV (Zehnder Condo 200) works fine without additional heat. Just don't install the supply vents where they'll blow directly on people. Ours are in the ceiling or high on the wall and there is no draft, warm or cold, at all. Using resistance heat is less efficient than using pv and heat pumps.

  14. syadasti | | #14

    Stephen the in-line heater offered by various brands is for core defrosting when the in take air is cooler than 25F for HRVs and 14F for ERVs in the Zehnder systems, it's not to heat your home. There are some ERVs like the Renewaire which by design don't need a defrost or recirculation mode but I think they still need outside air above 10F. You need the heater or you'll need to switch to recirculation or pause your HRV when it's cold enough outside, there's no way around that.

  15. this_page_left_blank | | #15

    Lance, performance data on Zehnder's ERV/HRVs is available on the HVI product database. Where did you read that the effectiveness of the bypass mode is overstated? I'm curious because that's one of the features I like about it. Getting very close to purchasing either a Zehnder CA350 or vanEE G2400.

    I have to say that I've changed my mind about buying an ERV then swapping the core only if needed. If I go with the Zehnder, that's exactly what I'm going to do. The HRV is more efficient, the core is cheaper. If it works, great. If humidity turns out to be a problem, I would buy the ERV core and then swap it in only during the time periods where it was warranted.

  16. syadasti | | #16

    Trevor, briefly mentioned above, but I had planned on buying the Zehnder with the HRV core and after a year or so swapping to an ERV when all the paint/adhesives/VOCs/etc have dried/dissipated from the new construction. My architect had agreed it was a good idea but when he got the quote he showed it only shows an ERV. Not sure if there's a reason or he just forgot about that idea? I hate how dry most homes/buildings get in the Winter.

    1. qofmiwok | | #17

      What did you end up doing, and how is it working? Theoretically with a tight house and an ERV, the house shouldn't be so dry. Have you found that to be the case?

      1. charlie_sullivan | | #18

        I'm not JM, but I do have a Zehnder and have both cores and and very glad I do: I use the HRV in the shoulder seasons and the ERV in the winter and summer.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |