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Comparing Actual Electric Boiler Operation Costs to Gas

D107 Member Posts: 1,810
Given electricity costs, at least in the NE, electric boilers don't yet seem viable but I so loved the idea of removing indoor combustion from the process that I've looked into it. A 15KW electric boiler (equal to a 51,000 input gas boiler) would appear to use 15kw per hour if not modulated. I gather they are considered 98% efficient--the 2% going to piping and jacket losses. Does that 15kw rating include the electric for the circulators, LWCO, etc? I'm guessing it doesn't, since gas boilers also use circs, etc. which is an additional electric charge to gas costs. We used 775 therms for heat last year, which @$1.50 per therm total, adds up to about $1160. 775 therms is about 77,500mbh divided by 3.4mbh per kwh = 22,794kwh x $.25per kwh = $5700. Plus maybe circ, lwco usage. Sound right? Guess I'll have to wait for those new Emerson-Oak Ridge Labs Air Source Heat Pumps, which could still be quite a few years.


  • Zman
    Zman Member Posts: 7,356
    It doesn't look like you accounted for the inefficiency of the gas boiler.
    Are you really paying $.25 per KWH?
    Check out this spreadsheet.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    EBEBRATT-Ed Member Posts: 12,149
    as @Zman correctly pointed out you didn't take the gas boiler efficiency into consideration.

    775 therms burned at 80% ?? efficiency on gas= net btus of 620 therms at a cost of $1160 for gas. (You have to buy and pay for 775 therms to get 620 therms of heat)

    620 therms (the heat you actually need) x 100000=62,000,000btu/3.41 btu/watt=18,181,818watts/1000=18,181kwh x $.25=
  • D107
    D107 Member Posts: 1,810
    Wow, thanks, great info, take me awhile to digest it. Re: electric charges, I counted supply, delivery, all other taxes and fees. Last month's bill was 441KWH for almost $114; that's almost $.26/kwh. Your table shows less than half that charge--a few years ago, yes--but obviously the area of the country you're in makes a big difference. As far as boiler efficiency, ours is an old WM about 75% AFUE. So to compare correctly do I just subtract 25% from the electric cost? Still not worth it.
  • D107
    D107 Member Posts: 1,810
    OK just saw Ed's explanation, thanks, so yeah even with boiler efficiency factored in, electric still costs 4x as much, at least in our area. So in what area of the country is electric $.06 kwh....

    And here's another example I found online:

    Simple example, if a gallon of oil costs $3 and has 140,000 btu's, that means you bought 46,666 btu's for a dollar (140,000/3). Now assume 82% efficiency, you get to keep 38,266 btu's in your house (46,666 *.82).

    A kilowatt hour of electricity (kwh) has 3,412 btu's. If a kwh costs $.25 , that means you can by 4 of them for a dollar = 13,652 btu's ( 4 * 3,412). To make things simple, lets assume 100% efficiency for the electric boiler.

    Based on this example, oil got us almost 3 times as much heat as electricity. You can go through a similar exercise for gas.
  • hot_rod
    hot_rod Member Posts: 16,557
    Hydro-Quebec has a tiered system that offers low rates. They estimate 50% of the residential customers heat with electricity. probably why there are numerous electric boilers manufactured in the area, Thermo 2000, Thermolec are a few brands we see in the states.

    Some homes I have been in have duel fuel boilers that use electricity to the limit, then automatically switch to gas.

    Industrial customers may be in the 3 cents range up there.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EBEBRATT-Ed Member Posts: 12,149
    Also I forgot to mention both gas and electric boilers need circulators and jacket and standby losses are about the same so they don't need consideration in the comparison
  • Jamie Hall
    Jamie Hall Member Posts: 19,150
    The obvious point is that the relative cost of electric vs. gas vs. oil is going to depend on your rates for each one -- and various areas are wildly different. As @hot rod notes, in Quebec electricity -- even full retail -- is insanely cheap (I won't get into the politics of that, which are messy) while in New England, just over the border, the rates are insanely high. You have to do the math for your specific provider!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Henry
    Henry Member Posts: 995
    Hot rod
    Yes the electric rates are cheap here. But for commercial applications, natural gas is a cheaper way to heat or use in a process system. Hydro Quebec has been mandated by the province to slowly bring the residential rates up. We do NOT do bi-energy with gas boilers. There are many residential oil/electric combination be it hot air or hot water. The consumer gets a better electric rate during non-peak hours or when above -12C. Below -12C, the electricity is billed at a higher rate. It becomes more economical to use oil. It is called the "DT" rates from Hydro Quebec.
  • jumper
    jumper Member Posts: 1,866
    It can get complicated if electric costs are time of day or you pay mostly by your maximum demand (instead of energy). In those cases if you have room for a big enough storage electric can be a bargain.