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Supplier advises nonstandard way to hook up a side tap gas WH for room heating

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Jells
Jells Member Posts: 566
in THE MAIN WALL
I have a several small apartment that are set up with a Bradford White M-1-XR403S6FBN or similar WH with side taps for DHW & room heating. I need to change out an 11 yo unit, and wonder again at the odd instructions given out by the large local supplier on how to set it up, which are contrary to the mfr instructions. They hand out a sheet that instructs to use the regular hot tap on top for the feed to the baseboard, and the top side tap for the return. They explain this saying that if you use the bottom return that when the circulator starts the large volume of cold water hitting the thermostat nearer the bottom of the tank can mess it up somehow. I didn't really follow how. They sell a lot of these "Genesis" heating packages of the heater with the bronze circulator and all the valves and checks required, so I want to give them the benefit of the doubt that they know what they're talking about. Any opinions? My guess is this was once necessary for much older models and they just keep advising it.

Comments

  • hot_rod
    hot_rod Member Posts: 22,142
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    Sounds like an "open" system where both DHW and heating water re the same. A controversial system, always has been.

    Usually those DHW combined tanks are limited to160F at the aquastat.

    There are instances where it would be bet to return that return to net the upper 1/3 of the tank, maintaining the Thermocline, and sticking the tank temperature.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Steamhead
    Steamhead Member Posts: 16,835
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    hot rod said:

    Sounds like an "open" system where both DHW and heating water re the same. A controversial system, always has been.

    If what HR says turns out to be true, I wouldn't touch it.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • JStar
    JStar Member Posts: 2,752
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    This set up is very popular in a few major NJ cities. We have seen the cold water problem before. It can also happen if they have A/C and a hyro-coil as well, which can cool the water and cause a ghost flow into the bottom of the tank, triggering the aquastat to fire the burner and overheat the tank which then eventually opens the T&P valve.

    I am not a fan of this system at all.
  • Jells
    Jells Member Posts: 566
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    Joe, that sounds like what they said. I still don't understand how that works. Fact is I have at least 3 different setups at this point, mfr recommended, supplier recommended, and one where the HVAC guys simply ignored the side taps and used the top ones. But they've all been pretty trouble free, one 12 yo tank leaked big time a few months ago, but that can happen to any WH.

    This system works great in my 450 sq ft units, and takes up very little space, unlike the 1st conversion from gas-on-gas, where the HVAC guys installed a minitherm & an indirect tank. It was expensive, huge, noisy and unreliable. These systems are dead simple, which allows me to maintain them myself easily, unlike the tankless condensing systems. And I'm not thrilled with the idea of punching 6" or 8" holes in my 100 yo brick building for the direct venting. But I've got 5 of these units and am open to ideas.

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