Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Electric & Propane domestic water heaters as master-slave

Hey guys, I was hoping for some help on domestic water heating from those with infinitely more experience than me on the matter, however I am brand new here, so please go easy on me.

I am in the process of installing a well water system from scratch and have one propane and one electric water heater, both 50 gallon and I am hoping to utilize them both to cope with high demand in the most efficient manner possible.
My thought was to connect them in series, with the electric heater as master, and the propane as a ready and willing slave - on account that I read that electric heaters are more efficient, and propane heaters can heat up water quicker (both things I am not certain about - but it sound like they could be true).
I am all good on the mechanical set up of all of this, but I have zero knowledge of the electrical set up, nor whether this is indeed even a good idea.

Therefore this is the part where I ask for help.
Is this recommended? And if not, what would be a better set up?
And if it is a practicable idea, how do I do that, and is this something I can perhaps do myself as a non-electrician?


  • Hot_water_fan
    Hot_water_fan Member Posts: 1,788
    edited January 24
    Hmmm. You already have both? 

    Likely the propane will be both cheaper and quicker to recover. So just use that, or go bigger and propane if it’ll fit. 

    To double check, because prices vary: 

    electric resistance $/mmbtu = $/kwh *293
    electric heat pump $/mmbtu = $/kwh *293/COP
    propane $/mmtbu = $/gallon * (1,000,000/91500) / COP 

    Surely the manuals have moved to different terminology? 
  • hot_rod
    hot_rod Member Posts: 21,813
    an intermittent high demand, when you have guests? If so just power on the more expensive to operate one at that time.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • PRR
    PRR Member Posts: 91
    > "I read that electric heaters are more efficient, and propane heaters can heat up water quicker (both things I am not certain about - but it sound like they could be true)."

    Think about it.
    If fuel/energy were free, we might not care about efficiency. Flushing a pint of pee with gallons of water is not real "efficient", but water has been too cheap to matter.
    Heating with fire usually leads to hot smoke we throw-away. Electric heat has no smoke (does have wire-loss). So there is that improved efficiency. Maybe 50% vs 95%.
    BUT electric is about the MOST EXPENSIVE heat you can get. Often twice the $/BTU of street gas. Even 3X the cost of coal (who heats bathwater with coal today??).
    This has some numbers but they all look old: https://www.amsenergy.com/fuel-cost-calculator/
    But that's after you buy the system. How much efficiency do you want to PAY for? Once you buy the tank, electric is under $100 of resistor, simple gas maybe $100 burner, and Heat Pumps (twice as efficient as simple electric, if you can dump the cold) used to be over $999 (but have come down, and get subsidies now).
    How fast? Anything "can" heat fast IF the pipe or wire is big enough. I have 4KW electric and it dims the lights on my 500 foot power wire. I sure could add a dozen more of those, or a 50KW beast, but my "120V" would sag to 40V (probably blow a main fuse). A bigger power line is $10,000 and up and up. OTOH street gas can be supplied in almost any quantity, and
    Guy's Gas's truck will come to the house and fill a tank 20 feet from a propane water heater. Or fuel oil or coal, though less popular. Refill every week, or more likely a 1,000gal tank or three so he doesn't have to deliver in the dark deep days of February.
    You really need to pencil trial numbers. I figured that two retired people don't use much hot water, or very fast, and that the standing-pilot in our existing on-demand gas heater was a large part of our gas consumption; and the dang thing ran cool and HOT (old valve). I brought in the cheapest electric storage heater, don't notice the increased electric bill, and the temperature is steady (until it runs out). A commercial laundry would have very different goals.

  • Jamie Hall
    Jamie Hall Member Posts: 22,889
    At the risk of upsetting certain of our members, may I humbly point out that electricity is NOT 95% efficient in today's settings, based on overall system efficiency. There are very very few places which have electricity supplied significantly by non-fuel fired sources (the fraction over time varies). The fuel fired sources are usually on the order of 30 to 40% overall efficiency, to which must be added grid losses.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • PRR
    PRR Member Posts: 91
    edited February 17

    ...electricity is NOT 95% efficient in today's settings,...

    You are correct at high level. Homeowner does not care. 95+% of the meter reading arrives as heat in the house or water. Fires, some or much of the bill goes up the stack.
    Of course THE reason electricity is more expensive per BTU is that the other 60%-70% losses have to be paid before the juice gets to the meter.
    I can burn gas in my cellar. Or I can have gas burned down by the river and the energy "piped" in a long chain of boiler (with smokestack), turbine, alternator, and miles of zigzagged cables. There is some economy in scale, but TANSTAAFL.