COMPARISON · HOME · ENERGY
A standard 1500W space heater running 5 hours a day at the U.S. average 18.34¢/kWh costs $41.27/month. If turning the thermostat down while you zone-heat saves 40% of a $160 central bill ($64.00), zone heating wins by $22.73 a month. But plug-in heat is $5.38 per 100,000 BTU vs $1.42 for a 95% gas furnace — so the win comes ONLY from heating less space, never from cheaper heat. Enter your own wattage, rate, and hours below.
The heater path multiplies wattage by hours, days, and your electricity rate. The central path measures how much of your monthly heating bill you shed by setting the thermostat down while you heat only the room you’re in. The verdict names the winner and the monthly dollar gap — and flags the one mistake that turns “saving” into added cost.
Heater cost = watts ÷ 1000 × hours/day × days/month × ¢/kWh ÷ 100 × heaters. Savings = central bill × % saved by turning it down. Net = heater cost − savings. At the defaults: 1500 ÷ 1000 × 5 × 30 × 18.34 ÷ 100 = $41.27/month for the heater; savings = $160 × 40% = $64.00; net = $41.27 − $64.00 = −$22.73 → zone heating wins by $22.73/month. If you don’t touch the thermostat, the heater just adds $41.27 to your bill.
Setup: one 1500W heater, 5 hours a day, 30 days, electricity at 18.34¢/kWh, a $160 central-heat bill, and a 40% setback saving from turning the thermostat down while the heater runs.
The heater’s monthly cost. 1500W = 1.5 kW; 1.5 kW × 5 h = 7.5 kWh per day; 7.5 × 30 = 225 kWh per month; 225 × $0.1834 = $41.27/month. Per hour it’s 27.5¢ — the number to remember if you ever catch yourself running it all day.
The central bill you avoid. Turning the thermostat down while the heater does the work saves 40% of $160 = $64.00. This is the entire win — without it, there is no win, only a bigger bill.
The verdict. $41.27 − $64.00 = −$22.73 — zone heating wins by $22.73/month, about $68 a winter quarter, for heating one room instead of the whole house.
Branch — central unchanged (honest info): savings = $0, so the heater adds $41.27 to the $160 bill. If the thermostat never moves, a space heater is not a saving strategy — it’s comfort spending, and that’s fine as long as you price it.
Branch — electric-furnace central ($350/mo, 40% saved): savings = $140.00; heater = $41.27; zone heating wins by $98.73/month. Electric central heat is expensive per BTU, so the setback pays off dramatically — this is the household type zone heating was made for.
Branch — 24/7 all-winter (12 h × 3 heaters): 1.5 kW × 12 h × 30 d × 3 × $0.1834 = $297.11/month — far more than the $64 you saved turning the central down. Running multiple heaters all day is the way the heater loses; zone heating only works when ONE room gets heat.
Branch — the gas-furnace honesty check: per 100,000 BTU delivered, a plug-in heater costs $5.38 (29.3 kWh at 18.34¢) while a 95%-efficient gas furnace costs $1.42 — gas heat is 3.8× cheaper per BTU. With a gas furnace, the setback still wins, but never tell yourself the heater’s heat is “cheaper” — it isn’t. The savings come from heating less space, full stop.
| Output | Formula | What it means |
|---|---|---|
| Heater monthly cost | W ÷ 1000 × h/day × days × ¢/kWh ÷ 100 × heaters | $41.27 at the defaults — what the plug-in heater adds to the electric bill. |
| Central bill saved | central bill × saved % | $64.00 at the defaults — the part of the central bill the thermostat setback erases. |
| Verdict & monthly gap | heater cost − central saved | Zone heating wins by $22.73 at the defaults — the number to decide on. Negative means zone heating wins. |
| Cost per hour | W ÷ 1000 × ¢/kWh ÷ 100 | 27.5¢/hour at the defaults — the quick mental number for “should I turn this on?” |
| Per-BTU honesty check | $5.38 vs $1.42 per 100,000 BTU | Plug-in electric heat costs 3.8× what 95%-efficient gas heat costs per BTU — the win is from heating less space, never cheaper heat. |
The math assumes the heater runs at full rated power the whole time — real heaters with thermostats cycle on and off, so a cycling heater costs less than this page says; treat the number as the honest upper bound. The 40% setback saving is a behavioral input, not a measurement — it only happens if you actually set the thermostat back 7–10° (the DOE’s guidance, worth roughly 10% per 8 hours) and keep it there; if you don’t touch the thermostat, tick the checkbox and read the added-cost branch instead. The purchase price of the heater isn’t counted — a $60 heater amortized over three winters is ~$7/month of first-year cost, worth subtracting once. Electric rates vary by state and season — the 18.34¢ default is the national average; New England and California run much higher, the South much lower. Demand charges and tiered rates can make the last kWh cost more than the average your bill shows.
Bright Side Kit. "Space Heater vs Central Heat: 2026 Winter Cost Verdict." https://brightoolbox.com/space-heater-vs-central-heat/ Accessed October 23, 2026.Data sourcesUsually only if you turn the central thermostat down. At the defaults, one 1500W heater for 5 hours a day costs $41.27/month; turning central heat down so 40% of a $160 bill ($64.00) disappears makes zone heating win by $22.73. Without the setback, the heater just adds $41.27 to the bill. Heat is heat — the win is heating less space.
Yes, when you actually commit to the setback. The U.S. DOE’s guidance: setting the thermostat back 7–10° for 8 hours a day cuts heating roughly 10%; dedicated zone-heaters who drop daytime heat in unused rooms report 30–50%. The calculator’s 40% default is optimistic — dial it to what you’ll honestly do, or the “win” is fiction.
About 27.5¢ per hour at 18.34¢/kWh (1.5 kW × $0.1834). That’s the number to keep in your head: an hour of heat is a quarter, five evening hours is ~$1.38 a day, and a full 8-hour workday is ~$2.20. At 8 hours a day for 30 days, the month prices out to about $66.38.
Because they’re measuring different things. Per 100,000 BTU of heat delivered, a plug-in heater costs $5.38 while a 95%-efficient gas furnace costs $1.42 — gas heat is 3.8× cheaper per unit of warmth. Zone heating wins only because you’re buying far fewer BTUs: heating one room instead of a whole house. Never claim the heater’s heat is “cheaper” — the savings are from less space, not better math.
No — never run one unattended or while sleeping. Keep the DOE’s 3-foot rule: three feet of clear space around the heater on all sides, plugged directly into the wall (never a power strip or extension cord), and buy a model with tip-over protection that shuts off when it falls. Half of home heating fires start with space heaters, per the NFPA.
1500W is the standard U.S. maximum for a plug-in heater — that’s the most a normal 15-amp household circuit handles comfortably. Smaller rooms do fine on 750–900W models, which cost proportionally less to run. Oil-filled radiators cycle more and feel steadier; fan-forced models heat the air fastest.
That’s where it shines. All-electric homes pay the electric rate for everything, so the setback against a $300–$400 central bill is huge — our branch shows a $98.73/month win against a $350 bill. In a gas-heated home the win is smaller but still real, because you’re buying fewer of those expensive-per-unit electric BTUs.