# Installing an electric water heater in series with boiler



## paul01420 (Apr 17, 2013)

Hi everyone,
I have an oil furnace that has a tank-less hot water that supplies my hot water. I am looking to install an electric hot water heater in series with my oil furnace. I have read multiple threads of people that have installed an electric water heater by hooking up the hot water return from the oil furnace to the inlet of the electric water heater. Then they would turn off the furnace during the non heating season, and during the heating season they would turn on the boiler. This allows the electric water heater to be fed with hot water from the furnace during the winter months (while the furnace is being used anyways) to help heat the hot water to save electricity. During the summer months the hot water would be heated completely with electricity so the oil furnace can be shut off thus saving the cost of oil being used just to heat the hot water.

My question is has anybody ever installed an electric water heater by installing the return of the electric water heater to the supply of the oil furnace tank-less supply? The reason why I would like to install the water heater before the oil furnace tank-less is because even during the winter months the water that supplies the oil furnace tank-less will already be hot and therefore save oil consumption my helping to keep the burner hot. If I install the electric water heater in series after the oil furnace then the oil furnace would still turn on when I am using hot water. Before anyone states that this is a waste of money because the electricity will be more expensive then oil, let me state that I have solar panels and will never use up the amount of electricity they are creating. Thus if I install the electric water heater in series with the oil burner (before the oil furnace instead of afterwards like most post suggest) during the winter months I would have the added benefit of helping to keep the oil furnace hot. My only cost would be the purchase of an electric water heater and then I would be completely saving money.

I would be interested in hearing people's thoughts about this. Also if you have done this and it is working for you, I would also enjoy hearing from you. Last but not least although this would not be a normal installation, does anyone know if this will pass plumbing codes? All replies will be greatly appreciated and thanks in advance.


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## Ebierley (Jan 19, 2013)

If you have unlimited electricity why not just use the electric heater.:whistling2:


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## paul01420 (Apr 17, 2013)

I will use electric heat and electric hot water heaters but I still plan on using boiler for January and February when it is really cold. If I used just electric heaters I would then run out of electricity. Also I would need to put electric in every room and I don't need this since I have the oil burner to supplement the electric heat. 

Thanks for your reply... does anybody else have any info on the original question I asked. Thanks in advance.

Paul


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## biggles (Jan 1, 2008)

are you going to use the HWH water for faucets and showers,cloths and dishes,in series with the boiler...in series with the tankless within the boiler is OK but not on the boiler room heating side.


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## beenthere (Oct 11, 2008)

Probably save yourself more money on oil. If you just use the electric water heater only. And convert your boiler over to a cold start boiler, so it never maintains temp. Only heats up when the thermostat is calling to heat the house.

Your idea is ok. But the water heater's water temp will still be fairly low compared to the boiler. So your burner would be coming on more then you think.


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## COLDIRON (Mar 15, 2009)

I was going to hook my daughter's electric water heater up similar to what you want to do.
I decided to just disconnect the coil from the boiler and just use the electric water heater and shutting off the boiler in the off season.

She's happy and everything is operating as it's supposed to.
Just one last thought, many people have thought about the same thing as you but in the long run it pays to just use the proper equipment for the purpose it's designed for. Usually it ends up costing more or headaches when things go wrong when equipment is used different than designed. 
Good idea though.


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## HVAC1000 (Dec 12, 2012)

maybe i am misunderstanding what you are saying but if you want to use boiler water for drinking that is a very bad idea, boiler water is not fit for human consumption as it becomes heavy mineral laced and partially acidic. if this is not what you were intending sorry but that is what it sounded like to me


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## beenthere (Oct 11, 2008)

HVAC1000 said:


> maybe i am misunderstanding what you are saying but if you want to use boiler water for drinking that is a very bad idea, boiler water is not fit for human consumption as it becomes heavy mineral laced and partially acidic. if this is not what you were intending sorry but that is what it sounded like to me



His boiler has a tankless coil in it. His potable water and boiler water never touch or mix with each other.


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## AllanJ (Nov 24, 2007)

If you connect the regular water heater's outlet to the furnace domestic hot water coil inlet then you need a bypass for the latter coil.

Otherwise the furnace turned off for the summer will sap all the heat from the hot water passing through.

In winter you would want to use only the furnace for heating the domestic water since otherwise the regular water heater first in line will do most of the work using (generally more expensive) electricity. So you need separate valves to close off the furnace coil and to close off the bypass.

In order to get stable hot water temperature the furnace must have a control (aquastat) triggered by the domestic hot water coil whether or not you preheat the water by leaving the regular water heater running.


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## agoodboy (Apr 5, 2013)

Paul I think I understand what you are saying but let me real picky and say I think sometimes you mean boiler when you say furnace (I never make mistakes myself LOL).

But I’m assuming you do in fact have the tankless coil as was pointed out in the post above. I have the same thing. They stink. In fact I have heard one expert repeatedly refer to them as the “thankless coil”. They are supposedly about the most inefficient means possible to supply domestic hot water. I’m going to replace mine one of these days.

But one thing I think you should know, something I have seen pointed out many times. Boilers that are used to being kept warm all their life may leak when they are converted to cold start. I don’t know how often that happens but it seems like some experts do say that. That has me worried a little.

You must have that triple Aquastat control, like I do, that keeps the boiler water temp from ever dropping to low for domestic hot water supply, hence your boiler may never have been allowed to grow cold.

Mine actually did get cold, not by choice for sure, when I lost electricity for days at a time. I did not develop leaks. So who knows?

Just something to think about.


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## AllanJ (Nov 24, 2007)

Boilers for hot water or steam heating systems over 50 years ago were sometimes constructed with stacked "rectangular ring" sections held together with long bolts and with putty or gaskets sealing together the various sections. Repeated hot cold cycles often caused the joints to leak after as many expansion and contraction cycles.


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