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Community and Q&A

Duct work

user-2340595 | Posted in Mechanicals on

Hey guys
In a recent post (spray foam insulated homes) there was a picture of a hrv and distribution box showing the white round plastic duct work leaving the box. Why can’t we use this type of duct work for our regular hvac duct work? I Would think this material would deliver air more efficiently than rectangular metal ducts. Installation would be easier as well.

Thanks for your help

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  1. GBA Editor
    Martin Holladay | | #1

    The type of ductwork that you saw in the photo was probably manufactured by Zehnder. As far as I know, you can buy plastic ductwork from Zehnder if you want -- without necessarily buying one of their HRVs. You'd probably have to talk to a sheet-metal worker to fabricate a distribution box that was compatible with Zehnder ducts and could be connected to a different brand of HRV.

    Another possibility is to buy a distribution box from Zehnder and modify it as necessary to work with a North American HRV. It would probably take some tinkering, but I don't see any reason why you couldn't do it.

    You should know, however, that Zehnder ductwork is expensive.

  2. PolarC | | #2

    The Zehnder type duct does not appear to have insulation. Depending on where you live in the country, flex duct requires R-8 insulation. Un-insulated duct from a furnace will lose heat thru the sides of the duct. Un-insulated duct from an ac coil (inside part) will sweat and warm up before it gets to the rooms it supplies.

    The ERV and HRV can use this because it is mixing room temp air with outside temp air. This is not as temp critical as the 125F heat and 45-50F cooling that the central air ducts supply.

    Flex duct is relatively easy to work with.

  3. GBA Editor
    Martin Holladay | | #3

    Thanks for your helpful comments. My response was based on a hasty reading of Rusty's question, and I assumed he was talking about using Zehnder ducts for ventilation, not a forced-air heating system.

    Rusty: As far as I know, Zehnder ducts are not intended to be used to move hot air. I don't know what their temperature rating is, but I would limit the use of Zehnder ducts to ventilation applications if I were you.

  4. Expert Member

    In some places the building code precludes plastic (combustable) ducts rom being connected to any heating system.

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