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    mtetter's Avatar
    mtetter Posts: 6, Reputation: 1
    New Member
     
    #1

    Nov 26, 2007, 05:45 PM
    Connecting a tankless water heater and separate hot water heater
    What I have is this. An oil fired boiler that generates hot water for my house baseboard heating system. Contained within the boiler is a tankless heater that is heated by way of the firebox in the boiler. The tankless heater is used only for domestic hot water. It has a separate CW supply to the heater and is not in any way connected to the house baseboard heating system. The hot water exits the tankless heater and into a mixing valve and thence to the house plumbing fixtures. This is the only hot water source for the house and therefore the boiler has to run 365 days/year. I would like to install a NEW electric hot water heater and pipe it into the existing cold water supply and the existing domestic hot water to provide hot water during the summer months and turn off the boiler, thereby avoiding the $800.00 fuel oil bill that I incurr for the summer. I can pipe the EWH into the existing system with values to bypass the boiler tankless heater. What I need help in doing is how to pipe the system and still use the boiler tankless heater as well as the EWH during the winter months. I invision a HW pipe from the tankless heater into the CW supply of the EWH. Would I need a check valve to prevent HW from back feeding into the CW system? Your help in resolving this situation would be appreciated.

    mtetter
    ballengerb1's Avatar
    ballengerb1 Posts: 27,379, Reputation: 2280
    Home Repair & Remodeling Expert
     
    #2

    Nov 26, 2007, 07:01 PM
    You just need to create a loop after the boiler where you install the new heater. The CW always flows to the boiler and in the winter its heat, in summer it isn't. When the water leaves the boiler you should install a three valve manifold like the ones used for a water softner. In the summer the horizontal valved is closed and the two verticles open to allow CW to enter the heater and the exit. In the winetr the horizontal is open and the verticles closed, no need for a check valve.
    mtetter's Avatar
    mtetter Posts: 6, Reputation: 1
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    #3

    Nov 27, 2007, 06:52 AM
    ballengerb1

    I'm not familiar with the 3 valve manifold. How is it piped?

    mtetter
    speedball1's Avatar
    speedball1 Posts: 29,301, Reputation: 1939
    Eternal Plumber
     
    #4

    Nov 27, 2007, 07:14 AM
    Quote Originally Posted by mtetter
    ballengerb1

    I'm not familiar with the 3 valve manifold. How is it piped?

    mtetter
    I think what Bal is referring to is a three valve bypass,(see image) and not a manifold. This will allow you to cut in or cut out the new water heater. Good luck, Tom
    ballengerb1's Avatar
    ballengerb1 Posts: 27,379, Reputation: 2280
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    #5

    Nov 27, 2007, 09:33 AM
    Tom, thanks for the graphics. Do you think my ideas will meet his needs?
    mtetter's Avatar
    mtetter Posts: 6, Reputation: 1
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    #6

    Nov 27, 2007, 12:19 PM
    ballengerb1

    The graphic does not really help. I do understand that connection.

    I want the EWH to be in the circuit with the boiler tankless heater in the winter months and the boiler tankless heater out of the circuit in the summer months. I want to use the HW from the tankless heater in the winter since the boiler will be running for the house B/B heat. I invision a couple of check valves where the HW from the tankless heater would tie into the CW supply of the EWH and also a check valve at the tankless heater to prevent CW from back feeding into the tankless heater in the winter time. What do you think?

    mtetter
    ballengerb1's Avatar
    ballengerb1 Posts: 27,379, Reputation: 2280
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    #7

    Nov 28, 2007, 08:46 AM
    Tom gave a hand drawn view of a soft water by-pass valve and this should work. The valve would be above your tankless heater. By operating the valves the way I mentioned in my earlier post you will have you two isolation loops. The check valves are not necessary since the water will simply flow through the shut down bolier without no significant problems at all.

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