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Community and Q&A

Zehnder ducts: ComfoFlex vs. ComfoTube (non UL rated vs. UL rated)

user-1102988628 | Posted in General Questions on

I purchased the a Zehnder ERV thinking I was getting the ComfoTube with the smooth interior which I believe superior to the ComfoFlex which looks a lot like standard flex dryer ducting. I received the COMfoflex instead. I didn’t realize at the time of the order that there was a ComfoFlex. I am investigating the issue and think that Zehnder sent the ComfoFlex because it is UL rated and the ComfoTube is not. I would like to use the ComfoTube. The question is can I? I am in CT and I cannot find information regarding UL requirements for fully ducted ERV. Any thoughts?

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  1. charlie_sullivan | | #1

    It's up to your local code official. Here in New Hampshire, a code official insisted on pulling out all the newly installed ComfoTube in a new build in a town adjacent to mind, because of that issue. I bought the take-outs for a bargain price and used them and my code officials were fine with it. I believe that the UL rating on the ERV unit and saying that the tubes were part of the same system may have helped. But more important may have been their relaxed attitude and my installer's friendly relationship with them.

    I still have some extra ComfoTube that I'd give away to a good home, or even to a pretty-good home.

  2. LaciB | | #2

    Thanks so much Charlie!

  3. Trevor_Lambert | | #3

    The larger ID of the ComfoFlex makes the flow approximately the same as Comfortable, according to Zehnder. Its OD is 1/4" bigger as well, so it doesn't quite fit into the same spaces. My building inspector gave me grief about Comfotube, but he was not swayed by ComfoFlex either. His concern, however unfounded, was the flow restriction of the smaller tube. He didn't care about the UL rating.

  4. LaciB | | #4

    I think the smooth interior of the comfotube would contribute to better flow.. more so even compared to flow in the larger ID of the flex. The flex feels like we are going backwards in technology.

  5. Trevor_Lambert | | #5

    They have spec sheets on their website, you can compare them. Obviously the flex tube is more installation dependent, with the need to avoid kinks and sags.

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