Oil fired & electric boiler at same time? HELP

Hard to tell, need better lighting. Something unique going on there.
Too bad the previous homeowner can't help you.
Looks like they probably use the electric on demand all summer, then when they put the boiler on in the fall they probably leave the electric off.
Probably close off the valves if possible so cold water doesn't flow thru the electric.
Unless your electric rates are low, you might find out that this doesn't save much money this way.
Better would be to let the boiler charge the storage tank.
---Or---
They have this set up to get constant hot water until the boiler's tankless coil catches up.

A few thoughts

your oil heater at one time has set up as a source for both heat and hot water


Are you in an area where a fuel delivery truck may have difficulty reaching your fuel tank with excessive snow on the ground? The electric boiler may be there to keep the home from freezing up.

I there an electric power generator on-site to use if the power fails? No Oil and No electricity with several days of deep-freeze will become costly, burst pipes, and all!

That is a common setup in your area to take advantage of extremely low electric rates. Some systems have automated switch over. It Is based on power plant production vs loads, not a time of day schedule
depending on which plan you chose it drops to something like $.06 per kWh

In this illustration, you will see some of the components of your system. this is not exact, but this is the best I could figure.

The cold water enters the boiler room from the top right of the illustration. From there it should feed the boiler fill valve (not marked) and the water heater at valve B. There may also be a valve D where the cold water feeds the tankless DHW coil in the oil boiler. Valve D should be closed in the summer and open in the winter when the oil boiler is operating. Valve B should be closed in the winter when the oil boiler is operating and open in the summer when the oil boiler is off. Be sure to turn off the electricity to the water heater in the winter when the oil boiler is operating. Valve A and C should stay open all the time (except for service) to allow for pressure relief from the respective vessels.

The heating system is feed by the fill valve to the boiler system. once the system is filled with water and properly purged of air, the numbered valves can be operated to as follows. to operate the electric boiler: turn off the oil burner switch, open valve 1, and close valve 3. To operate the oil boiler turn off the power to the electric boiler, Close valve 1, and open valve 3. The circulator pump may be operational by both systems or there may be a circulator inside the electric boiler (under the cover). The instructions are the same in either case if the wiring is done properly.

If you are close to Hydroelectric power and your electric rates are low... you will probably use the electric boiler all the time and leave the oil boiler off. If you need to operate the heat by a generator, the oil boiler will be less expensive to operate.

If you are not on Hydro-electric power from your utility, then oil heat may be less expensive and you will use the electric sparingly.

@shanzzie , I hope this information is somewhat helpful

Hydro Quebec used to have a residential rate where you paid something like 3 cents a kWh (several times less than most residential rates in the US and Ontario) and in exchange for this you agreed to switch your heating source to propane or oil (not wood because it had to be automatic) when the utility asked you to. Many homes in Quebec were set up for this at one time.

I forget what this rate was called but it was in place until their new dynamic pricing program started rolling out a couple of years ago. The new program base rate is 6 cents (still very cheap!) and it goes up at certain times, which is equivalent to when you used to be signaled to switch heating fuels.

Both the old and new rates would ask you to switch at any time that Hydro Quebec couldn't meet demand from their hydro and atomic fleet (didn't their lone nuke retire? maybe it's all hydro now), which have a super cheap, mostly fixed cost to operate. Supplying demand above and beyond what this fleet can supply can get really expensive really fast as they have to either import from adjacent systems or exercise call options on capacity from third party natural gas peaking generation in their footprint ($$$).

So, with today's rates you may be ahead running the electric boiler most of the time depending on the cost of oil, but be sure you are signed up for and understand whatever dynamic rate they have in place today.

Maybe someone already mentioned it and I missed it, but it looks to me like you'd be able to close the two blue handled gate valves on either side of the oil boiler and open the smaller red handled gate valves that go to the electric boiler and be in business. The way it's piped, the circ and air scoop would still be functioning with the electric boiler only

To preheat the DHW before entering the electric water heater the valves are configured as follows.
D open
X open
C open
Y closed
A open
B open
Z closed
Both the electric water heater is operating and the oil heat is operating

The electric boiler for space heating is off (switched to oil)

Also

This is the diagram of the heat pipes.


The original instructions for operating oil or electric are still the same.
Switch on electric Valve 1 & 2 are open. Valve 3 closed Valve 4 left open for expansion
Switch on Oil Valves 3 & 4 are open. Valve 1 closed valve 2 left open for expansion.

The small valve that feeds the boiler near the pipe that goes thru the wall can be open if the auto-fill valve is in good condition. You have a special expansion tank called a Fill-Trol. You must replace it with the same brand and model number expansion tank for the valve to work properly. If the valve fails, you might want to consider replacing both the expansion tank and the auto feeder valve with another design.

SO... Yes you can leave the valve open when operating either heating system. Both electric and oil use the same fill water valve.

OK, The only reason that I can think of doing that to the cold water inlet pipe is to preheat the cold water prior to entering the tankless coil. Since you are located near the Arctic Circle (Haha just kidding) your groundwater entering temperature might be rather low. The entering temperature of 14°C can be heated to 46°C or higher in NJ and maintain a constant temperature for an unlimited, time when I'm in the shower, using the tankless coil. If your entering water temperature is closer to 8° or 10° then your shower might not be so comfortable. I like a HOT Shower!

So the previous owner may have encountered that problem. To resolve, someone cut the cold water pipe near the tankless coil, opened up the rear panel of the heater, placed the cold water pipe near the steel boiler (that stays hot all the time to maintain DHW temperature) then routed the pipe back to the cold inlet of the tankless coil. Then he put the insulation over the pipe and covered up the pipe and boiler, then put the rear panel back on.

Pretty clever. IMO!

So, now that I'm sure of the piping, you may want to put labels on all the valves, copy these instructions, laminate them and hang near the boiler.

Off topic but related to labels... I had a brother in law that had a problem with purging the air from his system and a plumber would charge him Big$ to do a simple job. I labeled his valves and gave him instructions on how to do it. I could talk him thru it, over the phone because I knew what each valve did. Never paid a plumber after that.