Most plug-in space heaters top out at 1,500 watts on high. Run one on high for six hours a night and it uses 9 kilowatt-hours. At last January’s national average of 17.45 cents per kWh, according to the Energy Information Administration, that’s about $1.57 a night, or roughly $47 over a 30-day month.
Whether $47 is a bargain or a waste depends almost entirely on what heats the rest of your house and what you do with that thermostat while the space heater runs. The same goes for a smart thermostat: it can pay for itself in a couple of winters in one home and barely move the bill in another.
So skip the product pages for a minute and start with your heating system. The math below uses EIA’s January 2026 averages, since that’s when heating bills peak. Your own bill shows your actual rates, and they can be far from the average.
What a million BTU of heat costs, by source
Heat is sold in different units depending on the fuel, which makes it hard to compare. Converting everything to the cost of one million BTU of heat delivered to the room makes it simple.
| Heat source | Price used (Jan. 2026 US average) | Cost per million BTU of heat |
|---|---|---|
| Electric space heater or baseboard | 17.45 cents per kWh | About $51 |
| Gas furnace, 95% efficient | $13.96 per thousand cubic feet | About $14 |
| Gas furnace, 80% efficient | $13.96 per thousand cubic feet | About $17 |
| Heat pump in mild weather | 17.45 cents per kWh | As low as about $17 |
The space heater row is the one that surprises people. Electric resistance heat turns almost all of its electricity into heat, so there’s nothing wasteful about the heater itself. The problem is that electricity is an expensive way to buy heat. With gas at January’s average price, a gas furnace delivers the same warmth for a quarter to a third of the cost, even after allowing for its efficiency rating. A heat pump narrows the gap because it moves heat instead of making it. ENERGY STAR says an air-source heat pump can deliver up to three times more heat than the electricity it uses, though that advantage shrinks as outdoor temperatures drop.
This also settles the marketing question. Any 1,500-watt electric heater, whether it’s ceramic, oil-filled or “infrared,” turns 1,500 watts into the same amount of heat. Design changes how the heat feels and how fast a room warms up. It doesn’t change the cost per hour at a given setting.
When a space heater actually saves money
A space heater saves money only when it lets you heat less of the house. Three situations where it usually works:
- One person, one room, many hours. If you work from a home office all day, turning the central thermostat down several degrees and heating only the office can cost less than warming every room for one person.
- Bedrooms at night, in a house that’s already electric. If your home heats with electric baseboards, a portable heater costs the same per BTU as the baseboards. Heating one room with it while the others drop costs less than running all of them.
- A cold corner. A room over a garage or a drafty addition that never gets warm can make people crank the whole-house thermostat. A small heater for that room is cheaper than heating everything else to compensate.
And when it backfires: running a space heater while the central thermostat stays where it was. Then you’re paying for heat twice. In a gas-heated home, using a space heater to warm a large living room for a family is also a losing trade, because you’re replacing roughly $14 heat with roughly $51 heat for most of the people in the house.
A quick test before buying: write down how many degrees you’d lower the central thermostat and for how many hours. If the honest answer is “not really,” the heater will add to your bill.
Shopping for a space heater that won’t start a fire
The Consumer Product Safety Commission estimates that portable heaters, including electric space heaters, were involved in an average of 1,600 fires a year from 2020 to 2022, with about 70 deaths and 150 injuries a year. Most of the safety work happens at the store shelf, before the heater ever gets plugged in. Look for:
- A testing lab mark. UL, ETL (from Intertek) or CSA on the box or the label means the model was tested to a safety standard by a recognized lab. Listings on big marketplaces don’t always show this clearly, so check the product photos or the manual.
- A tip-over switch that cuts power if the heater falls, and overheat protection that shuts it off if it gets too hot inside.
- A built-in thermostat. A heater that cycles off once the room is warm costs less per hour than one that runs flat out. It’s the cheapest efficiency feature there is.
- A cord long enough to reach a wall outlet. CPSC says to always plug an electric heater directly into the wall, never into a power strip, and never to run the cord under a rug.
Placement follows the same logic. CPSC’s winter guidance says to keep all sides of the heater at least 3 feet from beds, curtains, sofas, clothes and papers, set it on a stable, level surface, and never leave it running unattended in a closed space.
What a smart thermostat can realistically do
ENERGY STAR puts the average savings from a certified smart thermostat at about 8% of heating and cooling bills, or $50 a year, and says some homes do better depending on climate and habits. The Department of Energy’s long-standing estimate is that turning a thermostat back 7 to 10 degrees for 8 hours a day can save as much as 10% a year on heating and cooling.
Those two numbers point to where the savings come from: setbacks while you sleep or are out. A smart thermostat makes setbacks automatic and easier to stick with. If you already lower the heat every night with a programmable thermostat, there’s less left for a smart model to find.
The payback math is simple. If a thermostat costs you $100 after rebates and your house hits the $50 average, it pays for itself in about two years. If your heating bill is small, or you already set back by hand, it takes longer. If you heat with expensive electric resistance, it can go faster.
Compatibility traps to check before you buy
- Electric baseboards. Most popular smart thermostats are low-voltage models built for central systems. Baseboard heaters run on 120 or 240 volts and need a line-voltage thermostat made for them. Some areas require an electrician for that install, so check before you buy.
- The C-wire. Many smart thermostats want a common wire for steady power. Some include an adapter. Take a photo of your current wiring before you shop, since most makers’ online compatibility checkers ask what’s connected to which terminal.
- Heat pumps. Pick a model that supports your specific heat pump setup, including auxiliary heat. A deep setback on a heat pump can lead to expensive backup heat when the system tries to recover in the morning.
- Cheap used units. Google ended support for first- and second-generation Nest Learning Thermostats on Oct. 25, 2025. They still work from the device itself, but app control, remote changes and updates are gone. A bargain listing for one isn’t a smart thermostat anymore.
Where the rebates are this year
Start with the ENERGY STAR Rebate Finder, which searches offers by ZIP code and has a smart thermostat category. Then look at your utility’s site directly. ENERGY STAR notes that most thermostat rebate programs are “bring your own thermostat” deals, where the utility pays you to enroll a device you already own in a demand response program. Read the terms: those programs let the utility nudge your temperature a few degrees during peak hours.
Don’t plan around a federal tax credit. The IRS page for the Energy Efficient Home Improvement Credit lists an end date of Dec. 31, 2025, so equipment installed this year doesn’t qualify.
If I were choosing one purchase for a typical gas-heated house, it would be the thermostat, programmed with real overnight setbacks, with a small certified heater only for a room someone uses alone for long hours. In a house heated by electric baseboards, the portable heater makes more sense, since it costs the same per BTU as the baseboards and lets the other rooms cool off. A line-voltage smart thermostat for the rooms you use most is the upgrade worth pricing there.
