How much electricity do residential oil/propane heating systems draw?
I am on the energy committee in my town. (It’s a volunteer committee that reports to the town government, promoting energy goodness to the municipality and residents.) Our committee recently was contacted by a resident in a rental home with a question about a mysterious spike in electric use.
The renter’s electric use jumped “from 726 kWh in November to a peak of 2,314 kWh in January” (an increase of 1,588 kWh). The December usage was middling between those figures. As the house relies on oil or propane (I’m not sure which) for heating, this was surprising to the renter. Her though was that something funny was happening unrelated to the heating system.
I am vastly ignorant on the intricacies of heating systems. However, I know enough to know that even a combustion boiler or furnace requires electricity to run fuel pumps, and hydronic pumps or duct blowers, etc. When I do back-of-the-envelope math, I get the following:
1,588 mysterious kWh…
744 hours in January…
Then 1,588 kWh / 744 hours = 2.13 kWh/hour
It seems plausible to me that an oil or propane heating system could draw that amount of electricity while running in cold weather, especially for a house that has “tons of windows and we’ve had trouble getting some of them to close with a tight seal.”
However, Google searching has left me empty handed on how much electricity non-electric heating systems draw. So here I am at this Q&A… am I on the right track, or at least a plausible track?
Thanks,
Jonathan
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Replies
Jonathan,
A gas furnace has several electrical components, among them the furnace fan (by far the biggest electrical load), an igniter, a draft inducer, and controls. Oil furnaces include an oil pump, an oil burner motor, perhaps a power vent unit, and a furnace fan. The AFUE gives no clues concerning the power draw required to run these electrical components, which varies from appliance to appliance.
Most furnace fans draw between 500 and 800 watts, with an annual electricity use that averages about 500 kwh per year. Furnace fans account for 80 percent of the electricity used by furnaces, so total furnace electricity use averages about 625 kwh per year. If a homeowner operates the furnace fan continuously — either to improve air mixing or to meet the needs of an electronic air cleaner — annual electricity use is much higher.
Martin, thank you. If it changes things more than a little around the edges, I've learned some more specifics: the system is baseboard hot water distribution heated with oil. You mentioned oil furnaces not having generic AFUE data on power draws. Is that equally true of boilers? (I'm under the impression that "furnace" refers specifically to hot-air units, and that "boiler" refers to either steam or hot-water units.)
Jonathan,
An oil-fired boiler is likely to draw fewer walls than a furnace, because most circulators require less power than a furnace fan.
I don't really know the average power draw for an oil-fired boiler would be, but you could add up the wattage required for the oil burner, the oil pump, and the circulators, and that would give you a pretty good idea.
Jonathon, I just installed a NG hot water baseboard system 42,000 BTU input with 1 circulator that uses 1.5 amps/hour at 120 volts 12 hours/day run time in January.
Electric cost for a month for this apartment;
1.5a
x120v
=watts/1000=.18KW
x12hours/day
x30days
=65KWH
x$.16/KWH
=$10.37 + $20 service
$20.37 For electric/month heat use
Natural Gas cost for a month for this apartment;
42,000 BTU fired
x12hours/day
x30days
divided by 100,000BTU/therm
=151 Therms used per month
x $.90/therm
=$136.08 GAS + $20 service
=$156.08 for gas/month of heat use
Total cost for heat NG and electric use
=$020.37 electric
+$156.08 NG
-------------------
=$176.45 January heat cost total
aj
Oil fired furnace with 2 electric loads circulator and oil burner
Circulator (adjust figures for your apartment)
1.5a
x120v
=watts/1000=.18KW
x12hours/day
x30days
=65KWH
x$.16/KWH
=$10.37 + $20 service
$20.37 For electric/month heat use
Running 24 hours a day would double cost of electricity
$30.74 for 130KWhrs
Oil burner uses 2amps if new effiicient type
add $27.65 for another 173KWhrs
Total 203 KWHra cost $58.39
Oil may have cost 4 times the cost of Natural Gas $156.08x4= $624.32
Total cost for oil heat= $672.34 for 12 hour burn/day for 1 month
Twice that for 24 hour run.... $1300 plus or minus
Martin, thanks again, and AJ two new thanks. The take away seems to be that the heating system is unlikely to be the mystery user of electricity here. Assuming AJ's system is anywhere near the same, his draws 0.18 kW (circulator) + 0.24 kW (boiler) for a total of 0.42 kW when running, while the mystery increase in electrical consumption at the rental house in question averages over the month to a constant draw of 2.13 kW. AJ's system is 1/5th that of the mystery load. Even allowing for a larger and older/less efficient system, and assuming 24-hour run time, 5x the draw seems unlikely. Maybe not impossible, but not an obvious solution.
So much for my amateur sleuthing.
Old worst case set up for a larger apartment
1.2KW/hr
x18hrs/day
x30days
650 KWHrs
x$.25/KWhr (my worst case electric cost this winter)
$160 for electric for this old inefficient oil boiler example
1600KWhrs
running 75%of the day which is a lot is 540 hrs
=
3KW/hr/120V=25amp load... NO WAY....
Someone is using portable 1500 watt electric room heaters..... YES WAY
I find "Amish heaters" in half the homes I enter....
aj
This is my vote. Some sort of resistive heat somewhere.
A "spare" 2 kilowatt load is something that should be pretty easy to spot. Even running 24/7 an oil fired hydronic system isn't going to use that much power even with ridiculously oversized pumps.
Don't rule out the potential of a flaky and misbehaving electric meter as the culprit.
If the domestic hot water is electric and somebody is taking 10 showers per day you could get there.
The spike in electricity could be caused by a sump pump. A heavy rain and a leaky basement will cause the pump to run continuously over days. They consume a lot of electricity.
Deleted
You realize that this thread is close to 6 years old, right?