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Thread: Hydroair Water Heater plumbing

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    DIY Junior Member karter56's Avatar
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    Default Hydroair Water Heater plumbing

    I am installing a new water heater for my hydroair furnace. The system was installed 22 years ago and they had the cold coming into the water heater, then out to a circulating pump, through a check valve, through the air coil and back to the drain at the bottom of the heater. I was thinking it would be smart to install a expansion tank in the cold line. Do I need to install a check valve before the expansion tank?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Is the WH dedicated to only heating the house, or do you also use it to heat water for household use? You should realize that most WH are not designed for this, while they may work, they are nowhere near as efficient as a boiler which is designed for constant firing.

    Assuming it's a closed system, then yes, you need an expansion tank designed for a boiler, not one designed for potable water. It should be before the pump and no, it does not need or want a check valve - it must be open to the supply line. If this is potable water and not a closed system, the expansion tank, if needed at all, would be on the cold inlet to the WH. To use an open system, all pumps and other fittings must be rated for potable water. This means either a bronze or stainless steel pump along with any check valves, or whatever else may be in the system. Open systems have the big potential of polluting your water, and you must be very careful on the design when using one for heating purposes...you could have a stagnant loop, and over time, it could grow some really nasty things.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member karter56's Avatar
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    Thanks for your response. I actually separated the two systems. The old system had 2 water heaters in a series. I just installed a 50 gal unit going to the house. I have a 40 gal unit for the heating system. So you're saying no check valve or expansion tank on the supply line and install a boiler expansion tank on the hot side and then the pump. Does it need the check valve after the pump like they had installed before? Should the return out of the air coil be going into the drain?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    You need a proper check valve, backflow preventer on the incoming water to the WH, but normally, the supply valve would be turned off once you get the system up and running, the air purged out, and pressurized to at least a nominal 15psi. You could use an autofill valve, set ot around 15psi. Without some extra safety controls, this is potentially very unsafe. A WH only has a T&P valve, normally you'd also have a minimum pressure cutout, and potentially some other stuff. I'm not sure it makes that much difference whether you ran the return into the cold inlet, or the drain as long as it is after the backflow prevention.

    Personally, I wouldn't do this. WH aren't designed for the constant use of a heating system and aren't all that efficient compared with a boiler, and a boiler would have all of the required safety circuits in it as well.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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