Need to install an electric hot water heater with Oil fired coil

[acesneights1]

that title maybe confusing. I have a hydronic boiler with a tankless coil. It sucks. The house has solar and I want to locate an electric HW heater more central to the domestic plumbing where as now by them time the hot water comes from the tankless coil, its almost out. The location was not easily ventable somthat leaves Electric or Indirect. Solar electric makes electric cheap and I got a like new AO Smith 50 gal off CL for 150$. I wanna keep the coil in line and then do an H style bypass at top of electric. I realize this can cause a potential problem is someone shuts the valves and not the power to the elec HW heater so I will put a ex tank post CW valve on top of elec HW. The reason for bypass is if power failure I can still get HW from boiler of generator. Opinions ?

 

[johneh]

I may be off the mark but if you shut the water off to the electric tank
there in my little mind there should be no problem The stat in the tank will
cycle on and off as needed . water can not leave the tank because
there is no water to replace it . No water in No water out
But I'am not a plumber so what do I know ?

 

[acesneights1]

I may be off the mark but if you shut the water off to the electric tank
there in my little mind there should be no problem The stat in the tank will
cycle on and off as needed . water can not leave the tank because
there is no water to replace it . No water in No water out
But I'am not a plumber so what do I know ?

The problem with shutting the valves to the electric to bypass it is if someone screws up it could build pressure. It has a relief but I’m thinking an expansion tank between the cold water ball valve and the elec HW heater as a precaution.

 

[acesneights1]

Like this ....

 

[fbelec]

be careful if the tank makes a vacuum it could implode so valve the hot coming out of the tank and the hot coming out of the tankless coil and keep the cold vent live all the time

 

[maple1]

I might be tempted to just run them in series, for simplicity sake.

How long are your power outages? We use no DHW at all in an outage here, but outages more than 24 hours are a rarity.

 

[Don2222]

Hello
I did something very similar.
I have an indirect of this newer boiler and I put in an on demand electric panel. I plumbed it in a tri-state mode where I can use just the boiler or just the hot water panel. The third state and you may want to consider this, is to pull the water through my indirect instead of the very cold ground and then send it thru the electric on demand panel. Because I have a pellet stove in the basement, it heats up the indirect to almost 80 degrees so the electric hot water panel only has to go from 80 to 135.
In your case the 3rd state would be to pull water thru your electric before sending it to the tankless coil so the warm air in the basement makes it easier for the boiler to heat your hot water.
Here is my setup with Pex and shark bites from Home Depot.

 

[maple1]

Hello
I did something very similar.
I have an indirect of this newer boiler and I put in an on demand electric panel. I plumbed it in a tri-state mode where I can use just the boiler or just the hot water panel. The third state and you may want to consider this, is to pull the water through my indirect instead of the very cold ground and then send it thru the electric on demand panel. Because I have a pellet stove in the basement, it heats up the indirect to almost 80 degrees so the electric hot water panel only has to go from 80 to 135.
In your case the 3rd state would be to pull water thru your electric before sending it to the tankless coil so the warm air in the basement makes it easier for the boiler to heat your hot water.
Here is my setup with Pex and shark bites from Home Depot.

I think I would put coil before electric.

But we don't know if OP has a cold start boiler? Guessing not. Or he wouldn't likely have a coil.

 

[Don2222]

I think I would put coil before electric.

But we don't know if OP has a cold start boiler? Guessing not. Or he wouldn't likely have a coil.

If you put the coil before the electric then the coil would be heating the cold water from the well or the street instead of warmer water from the water sitting in the electric tank?
Is there any other reason?

 

[maple1]

If you put the coil before the electric then the coil would be heating the cold water from the well or the street instead of warmer water from the water sitting in the electric tank?
Is there any other reason?

Well, we still don't know much about the OPs boiler. But my thoughts were that in the summer, you could turn the boiler off or way down to reduce or eliminate standby heat loss. Which is the main bad thing about tankless coils - they waste so much heat up the chimney or out the sides. In which case, if you heat the water with electric then pass it through the coil, you would be transferring electrically heated heat into the boiler water which would then get wasted in said standy heat fashion. In winter if the boiler is up to temp, it would pass hot water to the electric heater and it might not need any electric heat added to make it usable. Or if it did, it wouldn't be very much.

We had a tankless coil in a wood/oil boiler for 17 years. I don't know how much of our valuable oil it sent up the chimney in standby heat loss when heating our DHW all those summers - but it was a lot. Plus made the house hotter than the outside temps were already making it. We should have switched to all electric way sooner than we did - tankless coils are the devil.