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FVIR

Jim Davis_3
Jim Davis_3 Member Posts: 578
in THE MAIN WALL
I have had many comments about several water heaters manufacturers that no longer allow their FVIR water heaters installed with 80% induced draft furnaces. Does anyone have information supporting this? Apparently it is causing a failure of the over-heat TCO in the burner area.

Comments

  • Ed_26
    Ed_26 Member Posts: 284
    TCO

    Most of the failures I've seen are from dirty air screens, or water leaks. Haven't heard anything from Mfg. or suppliers.
  • Unknown
    Unknown
    Jim, I have not heard anything

    about mfr's. I have had several cases with draft induced furnaces and boilers causing poor draft with the FVIR water heaters. What we have done is seperated them from the common vent connector and piped them individually to the common vent. In all three cases these were into double wall common vent with single wall 3" or 4" draft hoods on the water heaters. We use a wye to connect into the common vent and the water heater above the heating unit.

    Used double wall all the way on heating units and water heaters seperately flued.

    I felt the failure of the fusible link on the thermocouple was due to excessively high temps in the chamber due to poor draft. These units have high temps at the top of the units already some over 500 degrees. So poor draft does not help.

    Again I have not heard anything about mfrs stating they do not want them vented together.

    I teach in my classes to forget NFPA 54 which allows fan/nat venting and vent them seperately/
  • Mark Hunt_3
    Mark Hunt_3 Member Posts: 184
    Similar experience


    I heard rumors for the longest time that WH manufacturers were going to prohibit the use of their product when common vented with FA appliances. I never saw anything in writing.

    I specifically asked about this when I attended a training seminar given by a major WH manufacturer just as they were rolling out (no pun intended) their new FVRI line. The trainer had no idea what I was talking about. It stands to reason that the fusible link would break if the WH was not able to achieve proper draft as soon as the burner ignites. When the fan on the FA appliance kicks on, it stops the natural draft from the WH. I have seen it on every system I have tested. When the WH fires, there is ALWAYS spillage. That brief moment of "back pressure" if you will, could be enough to cause temperatures in the combustion chamber to get high enough to trip the FVRI device.

    We used a wye fitting as Tim has mentioned with some success. Installed vertically not horizontally. I was never really comfortable with that fix but the units tested within the allowable parameters. Every system we tested that had a tee fitting used to join the two units failed. Every single one.

    May the force be with you Obi Wan!

    Mark H
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