Comparison · Cost
The answer is not the same for every house, and any article that gives you one number is guessing. Here is the comparison done per delivered BTU.
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A space heater beats central heat only when you turn the main system down and heat one room instead of the whole house. Per unit of heat, natural gas is usually cheaper than electric resistance; the saving comes from heating less space, not from the appliance being efficient.
Before any arithmetic: a space heater saves money only if it lets you heat less. If your furnace thermostat stays at 70°F and a heater runs in the study on top of it, you have added a 1,500 W load to a house that is already being held at temperature. That is strictly more expensive than not owning the heater.
The saving comes from dropping the house to 62–64°F and heating only the room you are in. Everything below assumes you actually do that, because if you do not, no comparison is needed — the heater loses.
You cannot compare a furnace to a heater by looking at the appliances. The only common ground is cost per delivered BTU, which needs the fuel price and the appliance's efficiency.
For electric resistance heating the arithmetic is simple, because efficiency is 100%. One kWh is 3,412 BTU. At our published rate of 18.34¢/kWh, that is $0.0537 per thousand BTU delivered.
For a gas furnace, one therm is 100,000 BTU of fuel, and a modern condensing furnace converts perhaps 90–95% of it into delivered heat while an older unit might manage 80%. So the delivered cost is the price per therm divided by (100 × efficiency). The table below shows how that lands at several gas prices — look up your own price per therm on your gas bill and use the matching row.
| Gas price per therm | At 80% efficient | At 95% efficient | Electric at 18.34¢/kWh |
|---|---|---|---|
| $0.80 | $0.0100 / kBTU | $0.0084 / kBTU | $0.0537 / kBTU |
| $1.20 | $0.0150 / kBTU | $0.0126 / kBTU | $0.0537 / kBTU |
| $1.60 | $0.0200 / kBTU | $0.0168 / kBTU | $0.0537 / kBTU |
| $2.00 | $0.0250 / kBTU | $0.0211 / kBTU | $0.0537 / kBTU |
| $2.40 | $0.0300 / kBTU | $0.0253 / kBTU | $0.0537 / kBTU |
Delivered cost per thousand BTU = (price per therm ÷ (100 × efficiency)) for gas; (rate ÷ 3.412) for electric resistance. Electricity at 18.34¢/kWh (EIA, June 2026). Substitute your own gas price and your furnace's efficiency rating.
The pattern is consistent and worth saying plainly: per unit of heat, natural gas is typically two to five times cheaper than electric resistance. Even at $2.40 a therm on an old 80%-efficient furnace, gas heat costs about $0.030 per thousand BTU against electricity's $0.054.
If the house is heated by electric baseboard or an electric furnace, the fuel penalty disappears entirely — both are electric resistance at 100%, so a kWh delivers the same heat either way. In that case zone heating with a space heater wins as soon as you are heating less space, with no crossover to worry about. The baseboard comparison goes into this.
If your central heat is a heat pump, the arithmetic reverses hard and the space heater loses badly, because a heat pump delivers several units of heat per unit of electricity. That comparison is the one to read.
Ranked for fit, not for hype. Coverage and current draw are computed from each unit’s published wattage. Tap a row for the full write-up, or go straight to the listing.
| # | Product | Best for | Covers | Draw | Price |
|---|---|---|---|---|---|
| 1 | DreoNo photo Dreo Solaris 718The rare heater whose published coverage claim survives the arithmetic: 1,500 W is a genuine 300 sq ft at 10 W/sq ft, and Dreo publishes that number rather than implying more. | A whole living room | 150 sq ft | 12.5 A | Check price on Amazon |
| 2 | De'LonghiNo photo De'Longhi TRD40615TNo fan, so no noise and no moving dust — and the sealed oil keeps radiating after the element cuts out, which is why an oil-filled unit feels steadier than a ceramic one at the same wattage. | Silence, and a bedroom | 150 sq ft | 12.5 A | Check price on Amazon |
Coverage computed at 10 W/sq ft, average insulation, 8 ft ceiling. Draw computed as watts ÷ volts. Neither figure is a manufacturer claim.
Top pick · A whole living room
The rare heater whose published coverage claim survives the arithmetic: 1,500 W is a genuine 300 sq ft at 10 W/sq ft, and Dreo publishes that number rather than implying more.
| Published specification | |
|---|---|
| Rated power | 1,500 W at 120 V |
| Maker's coverage claim | 300 sq ft |
| Thermostat | 41–95°F digital, 1°F increments |
| Oscillation | 30° / 60° / 90° / 120° |
| Dimensions | 7.9" D x 7.9" W x 29.7" H, 8 lb |
| Safety | Tip-over cutoff, overheat cutoff, child lock, thermal cutoff |
| Heat type | Ceramic (PTC) |
| Maker’s coverage claim | 300 sq ft |
| Safety listing | ETL listed (stated by Dreo on the product page) |
Who it is for
A living room, bedroom or den at or under 300 sq ft with average insulation and an 8-foot ceiling, where you want to set a temperature and stop thinking about it.
What it is not for
A garage, an uninsulated basement, or anything over about 300 sq ft. It is not under-powered — 1,500 W is the plug-in ceiling — the room is simply too big for one outlet.
2 · Silence, and a bedroom
No fan, so no noise and no moving dust — and the sealed oil keeps radiating after the element cuts out, which is why an oil-filled unit feels steadier than a ceramic one at the same wattage.
| Published specification | |
|---|---|
| Rated power | 1,500 W at 120 V |
| Controls | Mechanical, with a programmable 24-hour timer |
| Fluid | Permanently sealed diathermic oil — never needs refilling |
| Maker's claim | Up to 75% more radiant surface area |
| Mobility | Front and rear handles, snap-on wheels |
| Heat type | Oil-filled |
| Maker’s coverage claim | None published — the coverage figure above is ours |
| Safety listing | No listing mark published in the listing text; verify the UL or ETL mark on the rating plate. |
Who it is for
A bedroom, a nursery at a safe distance, or anywhere the fan noise of a ceramic heater is the actual problem you are trying to solve.
What it is not for
Fast heat, and not a room you only occupy for twenty minutes. It also should never be tucked beside a bed or curtain — hot surface, 3-foot rule.
Cheaper to use a space heater only if you turn the central system down and heat one room. Per unit of heat, natural gas typically costs two to five times less than electric resistance, so the saving comes entirely from heating less space.
Roughly two rooms is the break-even against a gas furnace, and three rooms is clearly worse. Against electric baseboard or an electric furnace, zone heating stays ahead for longer because there is no fuel penalty.
Yes, when you heat one room instead of the house. The mechanism is volume, not efficiency — you are paying more per BTU but buying far fewer BTUs.
Not per unit of heat. Gas is usually two to five times cheaper per delivered BTU. A space heater wins only by heating a small fraction of the space the furnace would heat.
The only comparison where a space heater loses on physics: 1 unit of heat per unit of power versus 2–4.
Same physics, same cost per kWh — so the comparison is zoning, control and wattage.
The monthly figure at 4, 8, 12 and 24 hours a day — including the 24/7 case, computed.
The four units that get closest to a 300 sq ft room — and the two-heater arithmetic nobody publishes.
Room dimensions in, wattage and BTU out — with both corrections applied and the formula visible.
A correction, not a product pick: equal wattage means equal cost, and here is what actually varies.