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Musings of an Energy Nerd

Zehnder Develops a Ductless ERV

The Zehnder ComfoAir 70 competes with similar appliances sold by Panasonic, Lunos, and Vents-US

The Zehnder ComfoAir 70 ERV has through-the-wall ductwork that won't work in a 2x6 wall. The minimum wall thickness for this ventilation appliance is 12.5 inches.
Image Credit: Images #1, #3, and #5: Zehnder

Anyone who lives in a tight house needs a ventilation system. Unfortunately, most ventilation systems are expensive. If you decide to install a high-quality heat-recovery ventilator (HRV) or energy-recovery ventilator (ERV) with dedicated ductwork, your ventilation system might cost you between $6,000 and $8,000.

To address the demand for less expensive ventilation systems, one manufacturer of HRVs and ERVs, Zehnder, has just come out with a low-cost ($1,250) ERV that doesn’t need any ductwork. The ComfoAir 70 hangs on an exterior wall in your bedroom or living room. It’s installed like a space heater with through-the-wall venting: you drill an 11-inch-diameter hole through the wall, slide a cylindrical duct (split into two half-moon sections by a horizontal partition) through the wall, and hang the appliance on the indoor wall. (For a photo showing the partitioned duct, see Image #2, below.)

The appliance is designed to pull exhaust air from a grille on one side of the indoor unit and deliver filtered fresh air from a register on the other side of the unit. The ComfoAir 70 has four speed settings: 9 cfm, 15 cfm, 23 cfm, and 38 cfm. Power draw at high speed is 19 watts, while the heat-recovery efficiency at high speed is reportedly 72.9%.

The appliance doesn’t come with a plug; it requires a hard-wired 120-volt AC power supply. (The ComfoAir 70 is equipped with a transformer; its operating voltage is 24 volts DC.)

Like most ERVs, the ComfoAir requires regular maintenance (cleaning the heat-exchange core and changing the filters).

It shuts down when the weather turns cold

The ComfoAir 70 approach comes with a few compromises: it doesn’t work when temperatures drop below about 15°F; and the maximum air flow rate of 38 cfm is quite low. According to Zehnder, the appliance is suitable for apartments that measure 600 square feet or less. If…

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  1. user-4524083 | | #1

    ductless vents
    Martin - 1.) For the Zehnder unit, what happens if the wall is GREATER than 12.5"? 2.) Compared to the Zehnder, what is the potential downside of the Panasonic unit? The company has a good reputation for their exhaust only vents. Thanks for the article.

  2. GBA Editor
    Martin Holladay | | #2

    Response to Kevin Zorski
    According to this Zehnder document, the maximum permissible wall thickness is 600 mm (23.6 inches).

    The Panasonic unit has several disadvantages when compared to the Zehnder unit. Unlike the Zehnder unit, there is no way to attach a duct to the Panasonic unit. The Panasonic unit is not as efficient, and (as far as I know) has a narrower range of permissible outdoor temperatures. The Panasonic unit only makes sense in warm climates. (See the Panasonic map below.)


  3. green123dcra | | #3

    Mechanical System Beautification
    Dear gracious! If there are any more ugly mechanical systems to hang on the wall, I think I am going to puke. I think only energy nerds are going to love this. Please Zehnder, integrate this into a picture frame and make the vents go on either side of the picture like some mini-splits can do. I am also concerned about the possibility of re-breathing since it appears the exterior exhaust and supply are 4 inches apart and are moving in parallel but opposite directions.

  4. Yamayagi1 | | #4

    (Ukrainian) Vents-US also makes wall units similar to the Zehnder, the up to 35 CFM Micra 60, also available at Home Depot, and a new up to 71 CFM Micra 150. A call to Zoltan at Vents-US might let one know who is distributing them.

  5. GBA Editor
    Martin Holladay | | #5

    Response to James Kreyling
    Thanks for sharing information on Vents equipment.

  6. [email protected] | | #6

    further comparison
    Perhaps a more in-depth comparison would be of interest to many, including photos, cfm, efficiency, noise, etc.

  7. billdickens | | #7

    Does anyone know why Zehnder canceled this model? It leaves them without any product for the tiny home market.

  8. an123 | | #8

    Has anyone installed the Zehnder comfoair 70? I'm in Canada and just recieved a quote for one (just over $2000 CAD). I'm interested in it but can't find a single review online.

  9. elementsdesignbuild | | #9

    I am interested in using a single-room, through the wall, Lunos-type ERV for our new build. We are building a pretty good house, with in-floor heat in our concrete, above-grade foundation. We hope to recover some costs by getting a Efficiency Manitoba new-build refund. The Efficiency Manitoba consultant I spoke with said that the Lunos-type ERVs do not meet Canadian code for new builds. Is this correct? What else could we use, besides the $$$$ ducted ERVs?

    1. Expert Member
      Michael Maines | | #10

      Did the consultant say why they wouldn't meet your code? Lunos are very efficient, but they only move enough air for one or two rooms, so for a whole house you would need multiple pairs.

      1. elementsdesignbuild | | #12

        The house we are building is a granny suite with 1100 sq.ft., one bedroom. I think we could get away with 3 pairs: bedroom, bathroom, great-room. The entry/mudroom may need one, too.

  10. elementsdesignbuild | | #11

    The consultant said they'd been reviewed and did not meet code. I think I will call and ask for a copy of the review, so that I understand. Meanwhile, I need something and do not want the $$$ nor the noise of an ERV.

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