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Does anyone have experience with Zehnder ComfoFlex?

tdfontaine | Posted in Mechanicals on

We are building a new house and in the final stages of design. The design includes an HRV and Zehnder ComfoTube looked great until I discovered that it is not UL listed. So, I’m curious if anyone can provide feedback on ComfoFlex. There isn’t much on the intertubes…

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  1. Adam Emter - Zone 7a | | #1


    I just talked with a Zehnder rep the other day and he mentioned the lack of UL listing. Whether you choose to believe it or not, his argument was the UL listing means months (or years) of red tape and hundreds of thousands of dollars. He said they basically can't justify the cost since their US market share is so small at this point. Take that for what it's worth. On a side note, I really like the smooth inside of the ComfoTubes. I've looked at other similar products and came across ThermaFlex. They seem to be well made and some even carry a 10 year warranty. They are available on Amazon. Check out

  2. tdfontaine | | #2

    Thanks Adam for the info about Thermaflex. I can understand Zehnders business position however it's not worth the risk of installing ComfoTube to then be told by the building inspector that it's not code compliant.

    My next step might be to call a county inspector to get their input however I'm worried that if I say ComfoTube is not certified then the inspector has no choice to say it won't pass inspection.

  3. STEPHEN SHEEHY | | #3

    I'm puzzled. Why would the vent tubes need UL approval to be code compliant? Is the HRV unit itself UL listed?

  4. tdfontaine | | #4

    Stephen - I was reacting to posts like this -

    Makes me apprehensive to install a ComfoTubes to then be failed by the inspector. Maybe the answer is exactly as you suggested....the ERV is listed so the system should pass?

  5. STEPHEN SHEEHY | | #5

    Here in rural Maine, we don't need no stinkin inspections!

  6. user-3886229 | | #6

    Comfotube and Comfoflex has been rejected by code officials in areas here in MN and elsewhere across the US. In some cases after being installed. The UL issue is it's lack of flame retardent (smoke spread rating) in the polyethylene. Since it carries air and connects multiple living spaces this feels like a not very mysterious concern. Other than that it is a sweet concept. Given the current set of clear rules, selling it to unsuspecting consumers seems like a weak approach. We can disagree with the rule (or all rules!) but hoping for forgiveness after the fact rather than understanding and complying with written law often ends up poorly.

  7. user-1017420 | | #7

    Has anyone else had any confrontations with code officials concerning this issue. I am in Ontario, and very frustrated with the lack of consensus on this issue. My officials are being vague about the acceptability of product, but in other Ontario jurisdictions, it has been installed and passed without issue. The same can be said in other parts of Canada. Passive Houses in BC use the product regularly with no issues. Our National Building Code actually exempts the product as long as it used in a single dwelling and only for ventilation purposes, which is my case. The issue is flammability, but we can run meters of PEX and ABS, not to mention wiring covered in plastic, and of course the wood itself with all the glues and such in the ply or OSB. In and absolutely insane statement, the code actually permits asbestos-cement or clay piping as acceptable materials. REALLY!??

  8. GBA Editor
    Martin Holladay | | #8

    The code is the code. No one said it was logical or consistent.

    Most building inspectors have a lot of authority when it comes to deciding whether something is code-compliant. The fact that there is no UL listing for ComfoTube ducts is certainly a problem with some code inspectors. You'll have to discuss the issue with your local building department so that you can determine how flexible they are.

  9. user-1017420 | | #9

    Pun intended, I presume, Martin.......flexible.....that's good.

  10. Expert Member
    MALCOLM TAYLOR | | #10

    Can you be a bit more specific as to the NBC exemption for Comfotube? I can't find it anywhere.

  11. user-1017420 | | #11

    It appears to be in
    Depending on which province you are in, this may or may not be applicable. As Martin said, inspectors have some latitude in every direction.
    I can also be reached by email: [email protected]

  12. Expert Member
    MALCOLM TAYLOR | | #12

    Thanks Alec I missed that.clause. If the intent is to only allow combustible ducting where there is no threat of fire from a heat source that makes sense. I also see you can use it where the air temperature doesn't exceed 120 degrees C. I wonder if that effectively means you can use it to duct heat pumps? Any idea how hot their output is?
    BTW - that's great your inspector saw sense and passed your wall assembly. One less hurdle.

  13. user-1017420 | | #13

    Malcolm, It looks like a standard forced air furnace outputs at the furnace is around 125F (51C). As for using it for heat pump systems, I would expect the temps to be even lower. HDPE (what the tube is made of) has a melting point of around 260F (125C), so clearly this is a long way from furnace temps let alone heat pump. It really depends on where you plan on using the product Malcolm. If you were in BC, there would be no issue. I have spoken with some senior code advisers in BC, and they have sent me the intent statement, which is copied verbatim from the mNBC.
    If you're in Ontario, give me a call. If you wish.

  14. gareth_rose | | #14

    To me, the most attractive aspect of the Comfoflex is speed and ease of installation (the register connection system is elegant and fairly fool-proof).

    In situations when the lack of a UL listing is a concern, does anyone have a recommendation of other systems to consider that are quick to install (more so than your average flex duct)? The main goal would be to A) minimize leaks B) minimize the amount of site time required to run, connect ducts.

    Thank you in advance for any advice!

  15. blackmax | | #15

    We are struggling to get a Zhender unit here in Vancouver BC . The dealer has no proof that the ducting is approved for use here, neither the comfotube or flex. I’ve tried contacting Zhender but they do not respond. I have no issue installing it but the building inspector, installer and warranty people are not happy.

    1. Paulmcgee | | #16

      Morning, did you ever resolve the issue with comfotube in Vancouver? I am building on Vancouver island and wanting to use the comfotube, I'll be sending all the info to my inspector before I purchase to see what he says.

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