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Hot Water Heater Install Details?

Steve_in_NH Member Posts: 70
I'm looking for some help on the finer details of the hot water heater installation.

Background: Existing steam boiler with coil for hot water. Adding a hybrid hot water heater which will be located on the other side of the house closer to the kit/baths. We are going to use the steam boiler as a preheat in the winter.

Do I need a thermal expansion tank in this install? Recommendations on brand/size etc.

In the plumbers email to me, he mentioned having to install a mixing valve. I don't know where or why. Reading the water heater instructions it doesn't mention this other then to say that there should be a mixing valve at each fixture. He didn't mention multiple, so I'm assuming he is suggesting 1 right after the water heater. Would you do this?? Brand recommendations?

The water heater has a relief valve and two condensate drains, can they all be plumbed into the sewer pipe, similar to the washing machine.

Thank you.


  • dennis53
    dennis53 Member Posts: 53
    Across the river in Vermont, mixing valves are required in order to limit maximum temperature at the fixture to 120. Minimum temp at the water heater is 140, also required by code.
  • Jamie Hall
    Jamie Hall Member Posts: 17,103
    You can either use a mixing valve after the water heater -- or multiple ones at the fixtures. There are advantages to both.

    On the drains, they can all be plumbed to a sewer connection, but not into it. They must be separated from the sewer connection by an air gap. I used to require that the ends of any such drain be spaced at least two diameters of the receiver above the overflow edge of the receiver. Other folks may be less radical! But you do need an air gap.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Steve_in_NH
    Steve_in_NH Member Posts: 70
    Jamie, when you say "air gap" are you talking about a P-Trap, did you mean to say air trap?

    The previous owner had a stackable washer and dryer installed on the first floor for elderly. We removed the stackable and the pipe was capped. I was thinking I could utilized this pipe for the water heater. Either pipe the pvc over closer to the water heater, or run the three lines over to the existing location. It has a P-trap on it already.
  • Steve_in_NH
    Steve_in_NH Member Posts: 70
    I should add that the water heater location is about 5feet away from the washer drain location.
  • Steve_in_NH
    Steve_in_NH Member Posts: 70
    So I've discovered that all of the hot water piping from the boiler is 1/2" copper. All of the cold supply is 3/4" and steps down to 1/2" at the fixture locations.

    I want to use the hot water line coming for the boiler as my preheat for the new water heater. Is the 1/2" line going to be ok? Do i need to replace all this piping about 40' + feet. Is there another valve I could use like a mixing valve to increase the flow. I have a 1/2" cold water tap that could be connect for this purpose. Though now the preheated water is half as hot as it was. Does it even matter because its just filling the water heater tank so it would only matter in recovery, how fast it will fill the tank back up??