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Zehnder HRV Installation Issues

escyr | Posted in Mechanicals on

We have a Zehnder ComfoAir 350 installed in our pretty good house.  The unit itself is great, but a few mistakes were made during installation.  One of them has been bothering me since installation in 2016.

The drywall around the 125mm steel duct for the return diffuser (Zehnder UK calls them “extract valves”) were cut too large and the resulting hole was not able to be covered by the return diffuser.  This diffuser is a combination adjustment for the return air flow and a trim piece to cap the steel duct.  It is the portion that you see on the ceiling.  To remedy this, the installer glued on a wide plastic flange from a ceiling can light onto the return diffuser.  They did an okay job of it, but it doesn’t match perfectly.  The other issue, which is a Zehnder issue, is that when you use the Zehnder return diffuser filter, it covers the rubber seal, which doesn’t allow the diffuser to grip onto the steel tube very well and therefore it doesn’t sit flush against the ceiling, it leaves a gap.

Wondering if anyone has had these issues and what they did to remedy them or am I the lucky one?

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  1. escyr | | #1

    Pictures of the return diffuser filters.

  2. this_page_left_blank | | #2

    Similar experience, though the opening was only slightly too large on one side, and my drywaller was a complete hack, so no remedy was offered. Like yours, it hangs down a little bit because of the filter. My solution is just to avoid looking at it very often. If this was on my top 10 list of things that I wish I could fix on the house, I'd be pretty happy.

  3. user-2310254 | | #3


    You might be able to find a "goof ring" that fits the opening. I had an issue on my last house where the drywall crew "goofed" on all the recessed lighting cutouts. It seems to be a fairly common issue.

    1. escyr | | #4

      I didn't know about "goof rings"! Thanks Steve, I'll check them out.

  4. escyr | | #5

    I'd really like to take care of them not fitting up flush with the ceiling. I wish Zehnder had a different way of attaching the return diffuser filter.

    1. this_page_left_blank | | #6

      Have you tried putting the filter on first, then the rubber seal on top of it?

      1. vashonz | | #7

        This is what I did, otherwise it would slide out, leave a gap.

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