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Community and Q&A

Installing a Newer Model Zehnder ERV

qofmiwok | Posted in Green Products and Materials on

All the Zehnder documentation shows using the white rigid comfotubes which supposedly are super smooth on the inside and stay clean, plus quite rigid and don’t crush.  But what they shipped us was comfoflex tubes which are gray and much more flexible.  They said that’s been there standard for a few years not because it meets UL for fire code.

Anybody use these new ones?  It’s disconcerting to me that it’s different than what I’ve seen people use and even what Zehnder shows in their latest installation manuals.


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  1. GBA Editor
    Kiley Jacques | | #1

    I’m not sure if he was installing the same model as you are asking about, but here’s a post by Eric Whetzel documenting his experience installing a ComfoAir 350 Zhender ERV; he might be a good guy to ask.

  2. ERIC WHETZEL | | #2

    Appreciate the shout-out, Kiley!

    My understanding was that in some regions of the country installers were getting push-back from inspectors regarding the white comfo tubes as they are not UL listed.

    I thought the gray, flexible tubing was only a second, UL approved option. Maybe the gray tubing has become Zehnder's standard option unless a client specifically asks for the white comfo tubes?

  3. Kevin_Henry | | #3

    I had the same concern when our system was quoted in July 2019. This is what the Zehnder distributor told us at the time: "Comfotube is in the process of being discontinued – mechanical code is requiring all ventilation ducting to be UL181 compliant (fire code). HDPE ducting is being phased out in favor of steel wire/flexible fiberglass fabric ducting which is approved for UL181. We can still get the tube (HDPE) but it incurs a cost premium of 25% going forward, given we have to special order it. ComfoFlex is great, however. Very easy to install and splice, and is very durable."

    We decided to trust that they know what they're doing and stick with the quoted ComfoFlex. It has a larger interior diameter, presumably to compensate for the rougher surface.

    The manuals on the Zehnder America site do mention the ComfoFlex. (See, for example, page 6 of the General Installation Manual, which discusses the two options side-by-side.)

    1. jesjonesy | | #4

      How did your installation go with the comfort flex? Our inspector in CA is going to allow the comfortube but we have the flex in our order quote and don't really want to pay the premium. And honestly who know what could happen with an insurance claim if we have a fire and used no ul listed ducting. If it was a simple install without pinching or crushing at bends then we will go with the flex.

  4. qofmiwok | | #5

    I really would have preferred comfotube because I think the smooth sides helps keep dust from collecting, and dust is mold food, and my whole house is designed anti-mold. So I was very disappointed they sent me flex, and said tube wasn't an option. (Interesting that you were still able to get it in the states.)
    That said, I think it would have been way more difficult to install the tube. They were constantly cutting through studs and moving the tube from one bay to another to get it where it needed to go. You have to be way more thoughtful ahead of time about leaving framing spaces where you need them with the tube, or have tons of elbows.
    Although in a few places the tube would have fit better because it is less diameter.

    1. Maldahmba | | #6

      @qofmiwok - I am also working to design/build a mold preventative house and am encountering resistance with using Comfotubing because of the lack of UL rating, and I may begrudgingly have to use the flex ducting instead. How is your Comfoflex ducting working out? Are you feeling comfortable with its performance?

      1. qofmiwok | | #7

        I just posted a scathing review of it to be honest. Zehnder really doesn't support the US market and I wish I'd chosen something else. Latest problem is that the filters they sell with the CLD extract boxes don't fit with the Comfoflex tubes. We'll have to design our own solution.

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