A space heater saves money only when you're heating 1–2 rooms while lowering central heat by 8–15°F in the rest of the house. The break-even point for a gas-heated home is typically 2 rooms — if you need 3 or more rooms heated, running the furnace is cheaper. For all-electric homes, a space heater in one room while reducing central electric heat almost always saves money.
This isn't an opinion piece — it's math. Let's run the numbers for every common scenario.
The Core Economics: Cost Per BTU by Fuel Type
The fundamental question is: how much does each heating method cost to produce the same amount of heat?
The critical insight: Electric resistance heating (space heaters) costs $4.92 per 100,000 BTU. Natural gas costs $1.25–$1.50. That means gas central heat is 3–4× cheaper per BTU than a space heater. A space heater only wins when you're heating a fraction of the house.
The Break-Even Formula
Here's the math for whether a space heater saves money:
Space heater saves money when: Cost of (space heater running) + Cost of (central heat at reduced setting) < Cost of (central heat at normal setting)
Simplified: The space heater's added cost must be less than the savings from lowering the thermostat.
What Lowering the Thermostat Saves
The DOE estimates that you save approximately 1–3% on your heating bill for every 1°F you lower the thermostat over an 8-hour period.
| Thermostat Reduction | Approximate Savings | On $200/mo Gas Bill | On $300/mo Electric Bill |
|---|---|---|---|
| 5°F setback | 5–10% | $10–$20/month | $15–$30/month |
| 8°F setback | 8–15% | $16–$30/month | $24–$45/month |
| 10°F setback | 10–20% | $20–$40/month | $30–$60/month |
| 15°F setback | 15–25% | $30–$50/month | $45–$75/month |
Scenario Analysis: Gas Central Heat vs. Space Heater
Scenario 1: One Room Heated (Home Office)
Home: 2,000 sq ft, gas furnace (96% AFUE), $200/month gas bill. Office: 150 sq ft.
- Option A: Central heat at 72°F, all rooms: $200/month gas
- Option B: Central heat at 62°F + 1,500W heater in office (8 hrs/day, ECO mode ~900W avg):
- Gas savings: ~$20–$40/month (10°F setback)
- Space heater cost: 0.9 kW × 8 hrs × 30 days × $0.168 = $36.29/month
- Total: $160–$180 + $36 = $196–$216/month
Verdict: Roughly break-even to slightly more expensive. The space heater approach saves $0–$4/month at most. In this case, convenience (a warmer office) is the real benefit, not savings.
Scenario 2: Two Rooms Heated (Office + Bedroom)
Same home. Adding a 1,500W oil-filled radiator in the bedroom for 10 hrs overnight (ECO mode, ~800W avg).
- Option A: Central heat at 72°F: $200/month gas
- Option B: Central heat at 60°F + 2 space heaters:
- Gas savings: ~$30–$50/month (12°F setback)
- Office heater: $36/month
- Bedroom heater: 0.8 kW × 10 hrs × 30 × $0.168 = $40.32/month
- Total: $150–$170 + $76.32 = $226–$246/month
Verdict: $26–$46/month MORE expensive. Two space heaters exceed the gas furnace savings. Central heat wins.
Scenario 3: All-Electric Home (Heat Pump Central)
Home: 1,500 sq ft, electric heat pump central heat (COP 2.5), $250/month heating bill. Bedroom: 200 sq ft.
- Option A: Heat pump at 72°F: $250/month
- Option B: Heat pump at 62°F + 1,500W heater in bedroom (10 hrs, ECO ~900W):
- Heat pump savings: ~$25–$50/month (10°F setback)
- Space heater cost: 0.9 × 10 × 30 × $0.168 = $45.36/month
- Total: $200–$225 + $45 = $245–$270/month
Verdict: Roughly break-even. With an efficient heat pump, the savings from setback are proportional to the space heater cost. Marginal benefit at best.
Scenario 4: All-Electric Home (Baseboard/Resistance Central)
Home: 1,200 sq ft apartment with electric baseboard throughout, $350/month heating bill.
- Option A: Baseboards in all rooms: $350/month
- Option B: Turn off baseboards except in 2 rooms, add a 1,500W heater in the living room (6 hrs, ECO ~800W):
- Baseboard savings: Turn off 60% of baseboards → save ~$210/month
- Space heater cost: 0.8 × 6 × 30 × $0.168 = $24.19/month
- Keep 2-room baseboards running: ~$140/month
- Total: $140 + $24 = $164/month
Verdict: Saves $186/month! This is the ideal scenario for space heaters — replacing expensive all-room electric resistance with targeted zone heating.
The Break-Even Table
The golden rule: Space heaters save money primarily in two scenarios: (1) you have expensive electric resistance central heat (baseboard or electric furnace), or (2) you only need one room heated while aggressively lowering the thermostat in the rest of the house. In homes with gas central heat, the savings from space heaters are minimal or non-existent.
The "Occupied Room" Strategy
The most effective space heater strategy isn't about replacing central heat — it's about supplementing it intelligently.
The approach:
- Lower your central thermostat to 62–65°F (instead of the typical 70–72°F)
- Use a space heater only in the room you're actively occupying
- Move the heater with you as you change rooms
- Turn it off when you leave the room
- Use a timer for overnight bedroom use
This works because you're heating 150–300 sq ft (one room) instead of 1,500–2,500 sq ft (the whole house). You reduce central heat by 60–70% of the house volume.
Real-World Example: The "Follow Me" Strategy
The Rodriguez family (Denver, CO): Gas furnace, $190/month gas bill, 2,200 sq ft home. They lower the thermostat from 71°F to 63°F and carry a De'Longhi oil-filled radiator with them:
- Morning: Kitchen (6–8 AM, 2 hours)
- Day: Home office (8 AM–5 PM, 9 hours for one parent)
- Evening: Living room (5–10 PM, 5 hours)
- Night: Master bedroom (10 PM–6 AM, 8 hours, timer)
Math:
- Gas savings (8°F setback, 24/7): ~$25–$38/month
- Heater cost (ECO mode, avg. 850W, effectively 16 hrs/day): 0.85 × 16 × 30 × $0.14 = $57.12/month
- Net increase: $19–$32/month
They're paying $19–$32/month more for the comfort of being warm in the room they're in while the rest of the house stays cooler. It's not a savings strategy — it's a comfort strategy. And that's fine, as long as you know it.
When Space Heaters Absolutely Don't Make Sense
Don't use space heaters as primary heat if:
- You have natural gas central heat and need to heat more than 2 rooms
- You live in a high-electricity-rate state ($0.25+/kWh) — your costs will be extreme
- Your home is open-plan with no doors to close between rooms
- You have a heat pump system — it's already more efficient than any space heater
- You're heating more than 8 hours per day in multiple rooms — the math doesn't work
When Space Heaters Make Perfect Sense
Space heaters are the smart financial choice when:
- All-electric resistance home (baseboard or electric furnace) — zone heating with a space heater saves 30–50%
- One room needs extra warmth while the rest of the house is fine — supplemental use, not primary
- Brief heating needs — a home office for 4–6 hours, not 24/7 whole-house heating
- Rooms far from the furnace that the ductwork can't adequately reach
- Transitional seasons (fall/spring) when it's not cold enough to justify running the furnace but one room is chilly
- Rental apartments where you can't control the central system
Key Takeaways:
- Electric resistance heating (space heaters) costs 3–4× more per BTU than natural gas.
- Space heaters save money only when heating 1–2 rooms while dropping central heat 8–15°F.
- For gas-heated homes: break-even at 1 room, central heat wins at 2+ rooms.
- For electric baseboard homes: space heaters save $30–$80/month by zone heating.
- The "occupied room" strategy is a comfort play, not always a savings play.
- If you have a heat pump, it's already more efficient than any space heater — use it.
- The biggest savings come from insulation, not from switching heating methods.
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