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Using an electric water heater as an indirect.

Harvey Ramer
Harvey Ramer Member Posts: 2,239
I am looking at a Burnham oil boiler with a domestic coil in it. They also have an electric water heater. I am tieing the coil into the water heater with a circ. Does anyone have any experience with this? I am wondering what piping strategy would provide optimal stratisphication in the water heater. Also temperature switch sensor placement on the water heater? I am thinking sensor placement in the middle. I am putting a tempering valve in so it does not matter if the tank reaches high temps. I am going to dissect the Honeywell aqua stat control and use the low limit switch to turn on the dhw circ whenever the boiler reaches 140 deg. If there is no call for heat the boiler will be allowed to cool off completely. With this method I won't get a reverse transfer from the tank to the boiler and if a small zone calls for heat it will satisfy dhw demands while it's at it. If dhw calls for heat the boiler will have to reach 140 deg before the circ will energize.



Comments?



Harvey



Ps. The water heater will be switched over to electric during the summer.

Comments

  • Paul48
    Paul48 Member Posts: 4,469
    Cold Start?

    I think you'll be disappointed in the hot water produced.
  • Patchogue Phil_2
    Patchogue Phil_2 Member Posts: 304
    Keep it simple?

    Since you will be turning OFF the boiler in non-heating season anyway,  consider just (pre) heating the water thru the coil first then into the cold inlet of the tank.   The stratification issue *MOSTLY* takes care itself since the cold inlet should have a dip tube down to the bottom of the water heater tank.  You'd be putting very hot water down at the bottom - heat rises.



    You do not HAVE to recirculate the tank back through the coil.  Don't let the boiler temp drop for cold-start. If your triple aquastat LOW is set for 150*/160* with a 20* DIFF you will have plenty of hot water with the tempering valve.   The aqua-stat will allow the coil to be "priority" anyway - no need to dig into the wiring.



    With the rising cost of oil,  letting the electric elements heat the water could be cheaper depending on your cost of electric.



    Just my $0.02
  • JohnNY
    JohnNY Member Posts: 3,226
    Yes

    Look at A.O. Smith's piping diagrams for a 3-port domestic hot water storage tank.

    That's how you want to pipe it. I've done it and it works great using the surface mounted aquastat to turn on the boiler and pump along with an aquastat in the boiler.
    Contact John "JohnNY" Cataneo, NYC Master Plumber, Lic 1784
    Consulting & Troubleshooting
    Heating in NYC or NJ.
    Classes
  • Paul48
    Paul48 Member Posts: 4,469
    I

    feed through the coil in an oil-fired boiler to a 50 gal. gas hot water heater. My gas bill is about $20 a month,and I could fill my swimming pool with hot water. I know, you're talking different animals, but it just to show that the gas bill was kept to a minimum and I think the electric would be similar. Under ideal conditions, you'll get another 5+ years out of the boiler by not making it a cold-start boiler.
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,239
    I guess I should explain further.

    This will end up being a dual fuel system. Next year the homeowner wants a coal boiler installed.

    The current piping setup on the oil boiler is, three original zones, zoned with circs in a parallel piping configuration. There are three additional zones added, 1 baseboard and 2 radiant. They came off the end of the supply main and put in a 3/4" loop that runs back into the return main. They put a circ in this loop turning the parallel piping into kind off a primary-secondary. The additional zones come off of the new loop with closely spaced tees.

    Short of replumbing the entire boiler the best way I could figure to do it is to place a tee at the supply and return tapping of the oil boiler and circulating the water from the coal boiler through the oil boiler. The water heater will be tied to the oil boiler as I stated before. This will add mass to the system which I think is critical to be successful with coal. Oil will act as backup, emergency and such.

    But in the meantime I suspect the oil boiler to rarely completely cool off to a cold start. The house is micro zoned for a 109,000btu high mass boiler. That is why I want the dhw circ to come on every time the boiler reaches 140 deg. This should provide some buffer and keep the boiler from short cycling as much. Also there will be fewer calls for dhw if it gets satisfied every time a zone calls for heat.
  • icesailor
    icesailor Member Posts: 7,265
    Electric water heater as storage tank:

    I've installed them for over 35 years. I have one in my own house.

    Feed the water heater like it is a water heater. Cold into the top and hot out of the top, full size. Remove the bottom drain and replace it with a 3/4" brass tee and install a Taco 006 BT threaded brass or stainless steel circulator. Pipe that into the "cold inlet" of the tankless. Pipe the "hot outlet" into the cold inlet at the top of the water heater. The dip tube will send the hot water to the bottom of the tank for mixing. Use the bottom electric thermostat in the water heater to control the circulator. It will act as a single pole switch in series. You can use a cord whip to run the circulator You DO NOT need to wire the circulator into the boiler wiring. Set the low limit circulator to 140/150 degrees and the cooler water being pumped into the coil will start the burner. If there is a heat call, the low limit will still be working. You won't be getting any condensation in the boiler.

    This connection has always worked for me. I recently did one with a 199,000 BTU Noritz as the heat source. I ran into a problem because of the high demand and flow where the circulator couldn't overcome the incoming pressure when the water was running. The elements in an electric water heater, are 1" NPT. I removed the lower element and installed a 1" NPT Brass nipple and piped the tankless outlet into the lower element where there is a no pressure zone. It works well now.

    It works for me.
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,239
    Thanks for all the input guys.

    That's what I love about this site. The knowledge base is incredible.



    Cheers

    Harvey
  • Patchogue Phil_2
    Patchogue Phil_2 Member Posts: 304
    no pump

    ice



    I've been running my afore mentioned setup for 11 years,  with no extra pump.  I send the cold water through the oil boiler's coil first then into the cold inlet of my 50 gal electric tank.  Hot from tank goes to the domestic hot pipes. I did plumb for a bronze circulator off the drain but never installed it. 
  • icesailor
    icesailor Member Posts: 7,265
    Pumps:

    Before I can remember, I tried one without a pump. If you went for a long time without running hot water, and you didn't leave the boiler settings of 200 degree high m\limit and the operator at 180 degrees, you had very little stored hot water. If you went away for a few days, you came home to a cold tank. The pump was and is the solution for that problem.

    Without the pump, controlled by the water heater thermostat, you have very little control of the hot water.

    IMO
  • Patchogue Phil_2
    Patchogue Phil_2 Member Posts: 304
    lucky I guess! :-)

    Must be my family has been lucky with this setup here.  We must use just the right amount of hot water to not run out.  If the tank cooled down from standby loss while I was away for a week,  then the electric coil must have kicked in.  Either that or it is insulated just right and the boiler room is not cold.



    I use a 150* LOW during moderate weather and 160* LOW during Winter.  High limit is always 25* higher with a 20* DIFF.



    My 50 gallon tank is plenty hot.  In fact I have to temper the water at the shower lest I scald people.
  • icesailor
    icesailor Member Posts: 7,265
    Elements connected?

    You have the electric elements connected? Why would you do that? You could be easily running off the electricity and not off the boiler coil.

    The way I do it only uses the very low amperage if a fractional HP of a 006 circulator at 120 volts. Do you have your water heater/storage tank connected to a 240 volt, 30 amp circuit to run a 4500 watt element?
  • Patchogue Phil_2
    Patchogue Phil_2 Member Posts: 304
    240v/30a

    The heating elements are "live",  but they do not come on.  The temp of the water from the boiler coil is MUCH higher than the 125* setting for the heating elements.



    My water heater has indicator lights that glow when an element is getting juice.  Only saw the lower element glow once (after a very hot bathtub filling).  My electric bills are very low BTW.



    To tell you the truth,  at $4.00/gallon for fuel oil I am wondering when the electric elements are cheaper to use than oil for making hot water.
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