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Old 01-04-2009, 06:52 PM   #1
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Tankless coil in oil-fired boiler


I have a tankless coil for domestic hot water and the water is not as hot as I would like. Furthermore, I would like to shut off my boiler in the summer here in Connecticut. The kids have moved out so it is just me and my wife and I usually shower at the gym.

I could increase the water temperture setting on my boiler, but I don't want to do that, in part because I plan to add a radiant floor heat loop to the boiler and I want to keep the boiler water temp as low as feasible for this boiler.

My simplistic solution is to take the hot water out of the tankless coil into a standalone electric water heater. I can boost the hot water temperature electrically as needed, and can shut down the boiler in the summer.

I would not put isolation valves on the tankless coil and allow the domestic water to run through the tankless coil winter and summer, picking up cheaper (?) oil-fired heat in the winter and gain no heat in the summer.

I would also relocate the mixing valve from the outlet of the tankless coil to the outlet of the electric water heater.

Am I missing a big issue here?

David

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Old 01-04-2009, 07:23 PM   #2
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Tankless coil in oil-fired boiler


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I would also relocate the mixing valve from the outlet of the tankless coil to the outlet of the electric water heater.

Am I missing a big issue here?
Ayuh,...

I'm pretty much headed the Same Way....
I'll be using a Gas fired Tankless waterheater for the summer months...

Why wouldn't you just Shut Off the mixing valve if you want Hotter Water,..??
I was told I absolutely Had to install a Mixing valve when I switched from an Electric tank heater, to the Coil that wasn't being used in the boiler heater....
I'm glad I had abunch of extra valving laying around,+ used it when I put that Mixing valve in,....
I isolated it after the 1st week,... Shut it Right Off....
I have no problem Tempering my own water at the faucet,....
Don't need no Tempering Valve....

Anyways,.... I see No reasons your plan won't work,... Perfectly....

The Electric waterheater will work all summer,+ be a Big reservoir all winter....

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Last edited by Bondo; 01-04-2009 at 07:26 PM.
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Old 01-17-2009, 05:16 PM   #3
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Tankless coil in oil-fired boiler


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Originally Posted by Bondo View Post
Ayuh,...

I'm pretty much headed the Same Way....
I'll be using a Gas fired Tankless waterheater for the summer months...

Why wouldn't you just Shut Off the mixing valve if you want Hotter Water,..??
I was told I absolutely Had to install a Mixing valve when I switched from an Electric tank heater, to the Coil that wasn't being used in the boiler heater....
I'm glad I had abunch of extra valving laying around,+ used it when I put that Mixing valve in,....
I isolated it after the 1st week,... Shut it Right Off....
I have no problem Tempering my own water at the faucet,....
Don't need no Tempering Valve....

Anyways,.... I see No reasons your plan won't work,... Perfectly....

The Electric waterheater will work all summer,+ be a Big reservoir all winter....
Hi Bondo,

I'm in the market for a gas fired tankless water heater and I noticed you have one. I changed over from an oil fired tankless water heater and hydronic heating systems last year b/cos of escalating oil price. The NY Boiler manufacturer said they are not allowed by code to replace the oil burner with a gas burner. I have a Carrier heat pump/gas furnance hybrid system but I'm still using remaining oil for only domestic hot water. I turn the boiler on for 5 minutes in the morning and five minutes in the evening to supply my needs. I want a gas fired tankless hot water heater to do that duty for domestic hot water only. I like being able to secure the furnace whenver i want instead of making hot water all day in a storage tank. What unit do you have and waht do you recommend?

Lucas
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Old 01-17-2009, 05:31 PM   #4
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Tankless coil in oil-fired boiler


I'm actually planning on having a new oil fired burner installed
I have an electric water heater & was planning on having a water heater coil in the boiler to boost/assist the electric water heater. Hoping to cut down on electric use
Then a solar hot water heater to assist in the summer/warmer months
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Old 01-18-2009, 09:48 AM   #5
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Tankless coil in oil-fired boiler


If you are still going to rely on the furnace coil for domestic hot water, you should arrange the pipes so the cold feed branches to both the coil and the water tank and the hot outlets from the coil and water tank merge with each other and the hot side of the plumbing system only. Use isolation valves at all four locations so the tank can be closed off completely in winter and the boiler closed off completely in summer.

If domestic water runs to the coil first and then to the tank, the water heater will have to kick on every now and then in winter.

Proper heating of the tankless coil requires that the water in the boiler be stirred up or churned. It may be necessary to have a separate "zone" with circulator pump to keep the coil heated when the zones for the house heating have cycled off. The latter might be nothing more than a short circuit from the furnace hot water output to the furnace return.

Last edited by AllanJ; 01-18-2009 at 09:52 AM.
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