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Community and Q&A

Is there a tankless venting equivalent of drainwater waste recovery devices?

ivZvQyaSfP | Posted in General Questions on

I was looking at wastewater heat recovery systems that wrap around the drain pipe. It got me a wondering – if my tankless exhaust gets so hot that I have to buy very special wall thimbles so it won’t start my house on fire, why shouldn’t one be able to tap into that?

The exhaust is already fan forced and slopes upward – is there still some minimum operating temperature needed for exhaust to function?

I was thinking about a similar question with regards to heat recovery from range hoods, but was directed to the idea that subtracting heat from the ventilation process would potentially cause issues with grease and smoke “condensing” – not the right term – on the too-cool ventilation surfaces.



Attached: two images of waste water recovery devices currently on the market.

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  1. davidmeiland | | #1

    You could easily cause the same condensation issue by removing heat from the flue of a tankless water heater (or any other combustion appliance). The hotter it is, the lower the chance of moisture inside the flue (which is acidic and can damage metal parts). Newer tankless units are much higher efficiency than older ones, and vent through plastic pipe at much lower temperatures.

  2. 4y23MuNF7N | | #2

    In the newer devices which vent through a plastic pipe, what happens to the acidic component of the vent gases ?

  3. GBA Editor
    Martin Holladay | | #3

    Most condensing furnaces and other types of condensing appliances require a condensate drain.

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