Mechanical Damper or not?

Discussion in 'Water Heater Forum, Tanks' started by pitteach, Jan 2, 2010.

  1. pitteach

    pitteach New Member

    Messages:
    27
    Location:
    Hamburg, NY
    I am replacing a 40 gal gas water heater. The current tank has a standing pilot that has a mechanical damper hooked up to the flue. The flue comes off the tank with 3" for about 2' and then opens up to the 4" metal stack that runs through a chase in the first floor, to the attic and out the roof. The water heater is the only thing using this stack because the furnace is 90+ direct vent.

    The question is: Can I eliminate the mechanical damper with the new HWT? In other words, what purpose is it serving?

    Tanks.
  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,491
    Location:
    Cave Creek, Arizona
    damper

    WHERE is the damper? If it is part of the water heater, then you cannot interchange it. The damper, depending on WHAT kind and where it is, should be to keep air from circulating through the heater to help maintain its temperature. Normally heaters with mechanical dampers do not have standing pilots because it interferes with the normal combustion.
  3. pitteach

    pitteach New Member

    Messages:
    27
    Location:
    Hamburg, NY
    The damper is not part of the water heater. It is mounted in-line on the 3" portion of the flue just off the top of the heater. It is wired to the gas valve. I do not know why it is there, I inherited the heater with the house. I would prefer to eliminate it with the new heater.
  4. Dana

    Dana In the trades

    Messages:
    2,805
    Location:
    01609
    The purpose of flue vent dampers on hot water heaters is to lower the air-infiltration into the house induced by an open flue when the appliance isn't firing. (It'll draft continuously otherwise, speeding up when the unit is firing.)

    You can remove it, but it may cost you a percent or so on your heating/air-conditioning bill. If your new heater is forced-draft it's a non-issue.

    But the bigger (and unrelated issue) is now that your furnace is no longer using the flue you may have long term chimney condensation/erosion issues, even wind-induced backdrafting if the flue is sized for a much higher BTU heating appliance (which it probably was) yet now has just the hot-water heater attached. Faced with installing a downsized liner to deal with the "orphaned hot water heater" problem (google it), it's usually cheaper to replace the HW heater with a power vented unit (side venting optional.)

    IIRC, the rule of thumb is that with a 3" HW heater flue, if the chimney flue is either 8" round or 7"x7" square or larger you're looking at trouble down the road if you don't install a narrower liner. If that's the case, go power vented on the hot water & side-vent it, brick-up the old flue & move on.
  5. pitteach

    pitteach New Member

    Messages:
    27
    Location:
    Hamburg, NY
    Thanks for the response. I was concerned that the damper may have been added to compensate for the loss of draft from the furnace. I guess that is not the case. The chimney stack is metal B-vent and I'm not sure of the size but it looks like it is larger than 6". I was considering the powervent model (Rheem) because that's what I have in my house and I like it a lot. The heater I am replacing is in a rental unit. It would be a piece of cake hookup out the side of the house. I am a bit concerned about the price because I installed one over the summer and it was a hair over $600, but the clerk at the supply house always manages to find me a nice scratch and dent deal. I don't mind spending the extra coin to get it done right and have it last.
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Forum Title Date
Water Heater Forum, Tanks Why don't gas water heaters have dampers to reduce standby losses? Jun 20, 2012

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