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takagi and chimney flue

The takagi or any other tankless water heater
says to use a rigid steel flue. However all the
liners for a chimney seem to be of the flexible type.
Does anyone know if this is ok?
The instant water heaters' manuals never talk about
an installation with the exhaust going up a chimney.

Assuming that the flexible liner is rated for a category III
gas device should I use the diameter
requested by takagi (4") or should I up it to 5"
in order to allow for the increased resistance to flow of
the flexible liner (because of the "ribs")?


  • DaveGateway
    DaveGateway Member Posts: 568
    Most tankless water heaters are DV only

    and should not be used with a chimney. Since they are not condensing, they must vent directly outdoors before flue gas temps drop. The units have no condensate drain and any would probably destroy the small heat exchanger very quickly.
  • but 30 feet

    but the takagi manual says the vent can be 30 feet in the vertical or horizontal. Why can't the 30 feet be up my chimney (only 19 feet total)?
    I don't think there is anything special about the chimney.
    The question is what kind of liner is suitable
    and if a flexible (ie ribbed) liner is ok
    should it be bigger than 4".

    Maybe the chimney is a special case. Is it?

  • H. Green
    H. Green Member Posts: 22
    liner for category III

    If the appliance requires a category III flue, that material should be used - even if as a liner of a pre-existing chimney.

    Most Listed special gas vents can be used as a chimney liner. Consult the manufacturer's instructions.
  • Mi39ke_2
    Mi39ke_2 Member Posts: 61
    Rep It

    Went to a dog and pony show recently regarding Takagi.

    From what I gather, if you don't direct vent immediately to the outdoors with your one unit, you can install a Field (or maybe Tjerlund?) exhaust fan and vent up a chimney or do multiple units. Check with your Rep, or call mine, as he seems to want to do things right.

    Rats! I don't have his number at this point. Drop me an email and I will get you some contact info if you need it: [email protected]. Or maybe look for the Rep of Wisconsin or Northern Illinois on the Takagi web site.

    Michael Ward
  • Bob Anderson_2
    Bob Anderson_2 Member Posts: 4
    Takagi Venting

    No - you must used CAT 111 pipe and not flex pipe.
    The Takagi TK2 and TKD20 can vent up to 35 feet with no elbows and less 5 feet for each elbow up to 3. If you want to go into a chimney - you will need to drop in CATIII pipe.

    Also, if you are going to put the flue in a cold area - get a Drip Tee for sure.

    www.houseneeds.com has this online


    Let me know if you need any more info.
This discussion has been closed.