Venting Navien Combi for high temperature design

Discussion in 'Tankless Water Heater Forum' started by cadobe, Jun 4, 2019.

  1. cadobe

    cadobe New Member

    May 25, 2019
    From the manual on page 44:

    "In high temperature applications, the exhaust temperature can exceed 149°F (65°C). In that case, you must use Schedule 40 or 80 CPVC or Approved Polypropylene in the USA or Type BH Special Gas Vent Class IIB (CPVC) or Class IC (Polypropylene) that conforms to ULC-S636 in Canada."

    Now, for the high temperature design can be used 2" CPVC Charlotte Pipe FlowGuard Gold which stands for maximum 180 degrees? Or needs to be CPVC schedule 40/80?

    Not sure which schedule is the Charlotte Pipe FlowGuard Gold.
  2. Dana

    Dana In the trades

    Jan 14, 2009
    Why are you going for a high temperature design? If you run the fuel use load calculation or a Manual-J you'll find that your design heat load is ridiculously low, and the cost of radiation sufficient to heat with 120F water isn't all that expensive. (My local out design temp is 20F colder than yours, and the heating system is set for 125F AWT with no more radiation than your Myson flat panels.)

    Seriously, running a room by room Manual-J using a sorta-real tool then sizing the rads for a suitably low temperature doesn't take much time. If using load calc and sizing the radiation for 140F water at the 99% design temp load would usually be good enough for running it at 125F due to the inherent padding that tool delivers.

    The cooler the water temp, the steadier and more comfortable the heat will be. Whether or not the NCB is so oversized that it never really modulates, running it under outdoor reset control and dialing in the curve will max out the efficiency until/unless you hit a temperature at which it short cycles. While it's nicer to the equipment if operated primarily in a modulating range, if the burn cycle numbers are low enough it won't be a terrible hit on efficiency or longevity.
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  4. cadobe

    cadobe New Member

    May 25, 2019
    Will see that. Anyhow venting problem solved.

    The 2" CPVC schedule 40 and schedule 80 share the same OD which is NOT same as 2" CPVC Charlotte Pipe FlowGuard Gold. A little confusing I know, but this is how it is. Moreover the CPVC Charlotte Pipe FlowGuard Gold is meant to be for water piping.

    If somebody will look for same pipe venting here is the link for the pipe I bought.

    Thanks Dana
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