Adding a Hot water heater...Already have Oil heat


Old 07-26-16, 11:28 AM
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Join Date: Jul 2016
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Adding a Hot water heater...Already have Oil heat

I am purchasing a home that has oil heat. The furnace is an older unit and replacing it at this time is just not possible. The water for the house is heated with the furnace (I assume from my limited research its a "tankless coil"?)
I'd like to add a hot water heater so I don't need oil to have hot water in the warmer months.

Is there any disadvantage of installing the heater in series. My plan would be to divert the domestic hot water line coming out of the furnace into the "cold" line of the hot water heater, then of course the hot line from the water heater would go to the house domestic line.

I guess the other option would be to install the heater in parallel, by diverting the cold line into the furnace to the water heater and cap off the Hot water line coming out of the furnace.

In a perfect would I'd love to replace the whole system but I just dont have it in the budget at this time.

Any advice would be greatly appreciated.

Old 07-26-16, 11:52 AM
Join Date: May 2015
Location: USA
Posts: 3,138
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What type of fuel will the new water heater use?

You should do a fuel cost comparison to figure out if you will actually save any money this way, especially if you add in the cost of the new heater and installation; payback may be a very long time.

Serial connection makes sense if you intend to use the furnace to heat water during heating season. You may have to leave the added heater turned on even during heating season when the furnace is running as otherwise the water in the added tank could cool down too much during periods of disuse. But as new tanks are well insulated, that water won't cool very fast so that probably isn't a concern except perhaps during vacations or other long absences. In any case, it wouldn't hurt to leave the added heater "on" all the time as it simply won't run if the incoming water is hot enough from the furnace.

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