Converting tankless coil on 1957 oil boiler to electric water heater

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Old 10-17-13, 12:10 PM
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Converting tankless coil on 1957 oil boiler to electric water heater

I bought my first house about a year and a half ago and it came with the original 1957 oil boiler with tankless coil. It has been serviced religiously and had a new burner put in a few years back. I've since added a wood burning stove and burned almost zero oil for heating last winter. I upgraded to a bigger stove this year and expect to heat exclusively with wood.

That leaves the monstrous oil boiler humming along at 150 degrees all day, all year, just to make hot water for the two people that live here. I'd like to add an electric water heater for domestic hot water and turn off the oil boiler for good. I would only turn it on only if I go away for a few days in the winter and aren't home to feed the wood stove, so the pipes don't freeze.

I'm trying to figure out the best way to hook everything up. I've read a bunch of info including this thread just a few weeks ago. I understand the risk of old boilers weeping, but it doesn't sound like there's much I can do other than hope for the best.

My understanding is that 1 is the cold into the coil, 2 is the hot out of the coil, 3 is a drain(?) and 4 allows water to bypass the coil(?).

My original thought was to hook up the electric HWH in series after the coil, so with the boiler off water would just run through it. Then if the HWH broke, I could revert to the boiler. I guess I could also plumb it in parallel with the boiler and then close 1 and 2 and open 3 and 4 to let all the water in the coil drain out.

What is the best way to hook this up?





 
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Old 10-17-13, 03:52 PM
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Jefferson... I'm hungry... I want some homemade smoked Andouille!

My understanding is that 1 is the cold into the coil, 2 is the hot out of the coil, 3 is a drain(?) and 4 allows water to bypass the coil(?).


Yes... and 4 is used as a "poor man's tempering valve" allowing one to mix cold with the hot so as not to injure someone with 180 tap water. If you were going to keep that, I would insist that valve be replaced with a proper thermostatic mixing valve.

My original thought was to hook up the electric HWH in series after the coil,
I wouldn't. We can talk about the whys and why nots at some other time...

What is the best way to hook this up?
I myself would abandon the coil completely. Cut the pipes and slip caps over the cut pipes. Don't solder the caps!

Hook up the new water heater and be done with it. Look into one of them fancy 'heat pump' electrics to save some money on 'lectricity.

Only way to tell if it's gonna leak when cold is to try it.
 
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Old 10-17-13, 03:55 PM
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Converting that boiler to cold start will require a full understanding of the controls that are installed on it now. I can't tell from looking at the pics how it's now controlled. It's likely not the same as the other thread you looked at with the 8124 aquastat.

We would need more pics, and you would need to trace lots of wiring and stuff...

Don't get any ideas about hooking up an Arduino to it either!
 
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Old 10-18-13, 08:09 PM
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Okay so skip the coil, tap right into the cold water line before boiler and then the hot out to the fixtures. Install a mixing valve.

I'd prefer not to cut the coil pipes if I can avoid it... can I just close off the cold in (1) and the hot out (2), open the poor man's tempering valve(4) all the way to effectively connect both ends of the coil so it's a loop, and open the drain(3) to let the water out and make a break in the loop?

I think I'm just going to do the manual boiler turn off rather than fuss with any controls. It's pretty infrequent I'm gone from the house in the winter for more than a day or two, and if so, I'll fire it back up a day or two before I leave just to be sure it works and then turn the thermostat down as low as it goes.

I did go with a heat pump water heater... hoping I can skip the dehumidifier in the basement this summer, we'll see.

Are you still in NJ? Want to help a guy install a hot water heater? I could see a lot of homemade smoked Andouille in your future....
 
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Old 12-14-13, 10:12 AM
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I got the GeoSpring hot water heater hooked up and it is working as expected. Yay for my first plumbing project going well.

I've also been leaving the oil boiler off as I generally heat the house with the wood stove. No leaking so that is nice too. DHW coil is valved off with the drain open so pressure doesn't build up in there (1 and 2 closed, 3 and 4 open).

I'm going away for the night and won't be home to feed the wood stove, so I figured I'd turn the boiler back on so the house at least stays 55 while I'm going. Boiler fired back up and brought itself up to temp/pressure, around 190 and 15-20 psi. When I change the thermostats and the zones call for heat, the circulator runs. When I turn down the thermostats, circulator stops and boiler stops.

Now I'm experiencing some strange behavior where it seems to be short cycling. Every few minutes it turns on and runs for maybe 1 minute, then turns back off. Any ideas where to start?
 
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Old 12-14-13, 10:47 AM
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Now I'm experiencing some strange behavior where it seems to be short cycling. Every few minutes it turns on and runs for maybe 1 minute, then turns back off. Any ideas where to start?
What's the temperature gauge doing when this is occurring?

Since you haven't done anything with the controls the boiler is still going to fire and keep itself warm... but that doesn't sound like what you are seeing? Not with those short cycles...

Gonna be hard to troubleshoot this one over the ether..........................................
 
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Old 12-16-13, 06:25 PM
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If you are going to keep the furnace tankless hot water coil in operation as a backup then connect it in parallel with the stand alone electric water heater. Install shutoff valves to isolate the part not being used.

You do not want the hot water out of the electric water heater going into the furnace coil when the furnace is not active in summer and you do not want the hot water out of the tankless coil going into the electric heater tank when that heater is not active in winter.
 
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Old 12-17-13, 08:08 AM
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Install shutoff valves to isolate the part not being used
This is really not a good idea.

Dead ends in any plumbing system present a possible health hazard in that they provide places for water-borne bacteria and cysts to live and breed.

Additionally, valving off and/or capping a hot water coil in a boiler can present danger of pressure building in the coil and possibly rupturing a pipe.

MANUFACTURERS recommend that when abandoning a coil in a boiler that it be left OPEN to atmosphere.
 
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Old 12-17-13, 10:59 AM
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The danger from bacteria etc. in the portion of the system not being used could make it impossible to keep the furnace coil ready for winter use. Hmmm. So that's why using "hot water" for food preparation or drinking is discouraged.

Otherwise (correction) the existing cold water inlet shutoff for the furnace coil together with the required cold water inlet shutoff for the electric water heater will suffice for winter/summer isolation purposes and not create closed off plumbing that could burst under pressure.

You would need to cut and cap pipes if you needed to isolate the coil or heater for maintenance and use the other for hot water in the meantime.
 
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Old 12-17-13, 11:34 AM
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But I believe the point is moot because he has already installed the new water heater from what I read in his postings. I believe he has also abandoned the coil in the boiler as recommended.
 
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Old 12-30-13, 11:00 AM
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Yes new water heater is in and the old coil is effectively abandoned, with the in/out valves shut and the drain valve open to prevent pressure buildup.

Also the short cycling issue seems to be resolved, although not exactly sure why. There is an Enterol 2-in-1 fuel saving control on the boiler which I think is a combination outdoor reset and DHW control of some sort? There are wire leads which run outside for what I assume are an outdoor reset and then there is this mechanical dial clock timer thingy which I think might be for DHW. It has on/off jumpers you place for various times of the day. I removed all the "on" jumpers and it does not short cycle anymore. However I don't think there's a way the boiler would know the temp of the DHW coil inside, so I'm not sure why this would have changed anything. Maybe just coincidence, who knows, but regardless it's running well again.



 
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Old 12-30-13, 11:29 AM
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It's some kind of a 'reset' control... never seen that one before though and a quick Google search doesn't turn up much at all.

If you want to give me all the information off the labels, I'll look further... but I would think that if at this point it ain't broke, then leave it be.
 
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