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Community and Q&A

Zehnder ComfoTube code issue

ALMds | Posted in Building Code Questions on

I am an architect working with a contractor/homeowner who is currently building a new home for his family in St. Paul, Minnesota.

He has installed a Zehnder HRV with associated Comfotube piping and insulated air intake and exhaust according to Zehnder’s layout and specification. However, our HVAC inspector will not approve the system as it does not meet their ducting requirements – it is not UL listed nor is it a type 0 or type 1 assembly.

It suffices to say that we are all extremely frustrated because at no time did Zehnder acknowledge that their system may not meet code. Not on their website, not when the order was placed and verified, and not on delivery. A simple, “heads up,” would have sufficed and would have allowed us to work with our inspector to find a solution before the system was installed.

We recently learned that Zehnder does have a UL listed product available for situations such as ours and they have agreed to cover the costs for the removal of the Comfotubes and the re installation of the UL listed system should it be necessary. We also learned that this has been an ongoing problem with Zehnder systems in certain markets throughout the U.S.

Has anyone out there had a similar problem? We will be applying for an Alternative Means and Methods exception and hope to have the system approved as is. We would like to avoid using the UL listed pipe, as it seems less robust and efficient as the Comfotube and would cause additional construction delays. Any advice as we apply for the exception would be appreciated. And if we specify Zehnder products in the future, we will make sure to talk with the code officials early in the process!

Thanks much.

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  1. GBA Editor
    Martin Holladay | | #1

    Thanks for your valuable post. I was unaware of this issue, and I am sure that other GBA readers will be interested to read about this problem.

  2. charlie_sullivan | | #2

    I've seen this issue from two perspectives. In one NH jurisdiction that is known for having very strict inspectors, the tubes had to be torn out of a newly built house and replaced. I live in a neighboring town which also has pretty strict inspectors. I took a chance and bought the tubes that had been ripped out hoping they'd pass inspection here. They did, without any major effort on our part. Because we didn't have significant trouble, I don't have any solid advice on what arguments are effective, but one thing we did make sure they knew is that the unit itself is UL listed and that the tubes are part of the same system. That's not a solid argument directly addressing the concerns but it might have helped frame the issue in a way that led to approval.

  3. ALMds | | #3

    Please see below for the city of St. Paul's resolution concerning the Zehnder system. They will allow the system only if it is connected to the smoke detection system and shuts off in case of incident. I am under the impression that they will not allow any installations of non-UL listed or non-code approved systems like this in the future.

    I encouraged Zehnder USA to continue to work to toward the UL listing of their products and to actively help change the residential building code to allow HDPE for ducting.

    I also requested that Zehnder USA inform its customers that their systems should be reviewed and approved by local code officials prior to ordering and installation.

    “The Zehnder HRV system has been installed at this address and during a Rough-In inspection it was asked of the warm air permit holder to provide information for the material being used to transfer air throughout the building (HDPE piping).

    The manufacturer has not provided information to reflect a UL tested material be allowed in the residential building. The information provided to me to date from you does not appear to identify a safety issue if the material is exposed to flame. Given the information and material reviewed to date, the following will be required in order for the Zehnder HRV product to be installed:

    The smoke detection system in the home shall be connected to the HRV system in order to disable the equipment if the smoke detection system is activated. This HRV system will be allowed to be installed at this property with an expectation and understanding that the manufacturer will pursue and obtain a UL testing for the duct material for future installations.”

  4. charlie_sullivan | | #4

    Thanks for the update. Turning off all ducted HVAC when a smoke detector trips sounds like a good idea for any house ... provided it's easy to turn it back on promptly if the issue turn out to be burnt toast.

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