Heating Cost Calculator
Enter the space you heat, how well it holds heat, and your climate. The calculator sizes the heater you need in watts or BTU, then prices a heating day and a heating month on electric resistance, a heat pump, and natural gas so you can compare.
How the math works
The sizing layer uses the standard rule of about 10 W of electric heat per square foot for average insulation in a moderate climate, scaled by insulation (poor 12, average 10, good 8, very tight 6.5 W/sq ft) and by climate (mild ×0.75, moderate ×1.0, cold ×1.25). That design load is what the room needs on the coldest stretch, expressed in watts or BTU/hr (1 W ≈ 3.41 BTU/hr).
Real bills come from cycling, not from running flat-out. During your heated hours the equipment runs a duty cycle - roughly 45% for an average room in a moderate winter, more for drafty rooms and cold snaps, less for tight ones. Daily energy is load × hours × duty; the calculator prices that energy three ways: straight electric resistance at your $/kWh, a heat pump at the same heat for 1/2 to 1/3 the electricity (COP 2.0-3.0 by climate), and a gas furnace at your $/therm with 80% AFUE.
Reading the results: why heat pumps win the comparison
All three rows deliver the same heat into the same room - the differences are conversion efficiency and fuel price. Electric resistance is 100% efficient but every kWh of heat costs a full kWh of electricity. A heat pump moves heat instead of making it, so one kWh of electricity delivers 2-3 kWh of heat. Gas sits between: cheap per therm, but a furnace wastes 15-20% of it up the flue. If your comparison shows gas far cheaper than resistance and a heat pump close to gas, that is the normal shape of the answer.
The cheapest kilowatt is the one you never need
Insulation moves every number in this calculator. Sealing drafty windows and adding attic insulation can move a space one full category (poor → average), which cuts the design load about 17% and the duty cycle with it - together often 30-40% off the bill, permanently. A programmable setback (8-10°F overnight) saves roughly 1-3% per degree for the hours it holds. Neither costs more than a month of the heating bill they erase.
FAQ
- How much does a 1500 W space heater cost per hour?
- 1500 W for one hour is 1.5 kWh - about $0.26 at $0.17/kWh, or $0.11 at $0.075/kWh. A 10-hour evening costs $1.10-2.60 depending on your rate. Note that a 1500 W heater is a room appliance: it cannot heat 600+ sq ft to room temperature in a cold climate, no matter how long it runs, because that space needs 4-6 kW of design load.
- What temperature should I set in winter?
- 68°F (20°C) awake, 60-62°F asleep or away is the standard efficiency guidance. Each degree of permanent setback saves roughly 1-3% of heating energy depending on climate. Programmable or smart thermostats automate this; manual setbacks work just as well if you actually remember them.
- Why does my heater cycle on and off?
- The thermostat cycles the unit to hold temperature, and the calculator's duty cycle models exactly this. Short-cycling (on-off every few minutes) signals an oversized unit or a dying thermostat; running nearly continuously during your heated hours means the design load exceeds the unit - the room will lag on the coldest days.
- Is it cheaper to leave the heat on all day at low, or off and reheat?
- For a few hours away, setback wins - heat loss scales with indoor-outdoor temperature difference, so a cooler house loses heat more slowly. For long absences (days), drop to 55°F to protect pipes. The old myth that reheating "costs more than it saves" is only true for very short absences of an hour or two.
- How do I convert between BTU, watts and therms?
- 1 W of heat = 3.41 BTU/hr, so a 5,000 W (5 kW) heater is about 17,000 BTU/hr. One therm of gas = 29.3 kWh of heat = 100,000 BTU. The calculator does these conversions internally; use them to compare a gas furnace quote against an electric one on equal terms.
This tool provides general estimates using rule-of-thumb sizing, not a Manual J load calculation or energy audit. Actual bills vary with weather, thermostat settings, and building specifics. Fuel-burning equipment must be vented properly and checked for carbon monoxide safety.