The short answer
A 400 W engine block heater costs about 7 cents an hour at the U.S. average electricity rate of 18.16¢ per kWh (August 2026). Plugged in 10 hours a night, 20 nights a month, that's $14.53 a month; on a timer that switches it on 2 hours before you leave, $2.91, saving about $46.49 over a 4-month winter.
The same heater in every state
A 400 W block heater 20 days a month for 4 months: 10 hours plugged in vs a 2-hour timer, at each state's average residential rate (August 2026).
| Alabama | $52.26 | $10.45 | 16.33¢ |
|---|---|---|---|
| Alaska | $94.11 | $18.82 | 29.41¢ |
| Arizona | $48.16 | $9.63 | 15.05¢ |
| Arkansas | $45.98 | $9.20 | 14.37¢ |
| California | $95.20 | $19.04 | 29.75¢ |
| Colorado | $54.94 | $10.99 | 17.17¢ |
| Connecticut | $78.43 | $15.69 | 24.51¢ |
| Delaware | $59.84 | $11.97 | 18.70¢ |
| District of Columbia | $83.14 | $16.63 | 25.98¢ |
| Florida | $47.97 | $9.59 | 14.99¢ |
| Georgia | $50.88 | $10.18 | 15.90¢ |
| Hawaii | $150.98 | $30.20 | 47.18¢ |
| Idaho | $42.78 | $8.56 | 13.37¢ |
| Illinois | $61.82 | $12.36 | 19.32¢ |
| Indiana | $54.46 | $10.89 | 17.02¢ |
| Iowa | $54.59 | $10.92 | 17.06¢ |
| Kansas | $49.50 | $9.90 | 15.47¢ |
| Kentucky | $44.16 | $8.83 | 13.80¢ |
| Louisiana | $41.18 | $8.24 | 12.87¢ |
| Maine | $102.75 | $20.55 | 32.11¢ |
| Maryland | $68.48 | $13.70 | 21.40¢ |
| Massachusetts | $97.54 | $19.51 | 30.48¢ |
| Michigan | $73.57 | $14.71 | 22.99¢ |
| Minnesota | $55.04 | $11.01 | 17.20¢ |
| Mississippi | $46.18 | $9.24 | 14.43¢ |
| Missouri | $51.26 | $10.25 | 16.02¢ |
| Montana | $49.82 | $9.96 | 15.57¢ |
| Nebraska | $43.33 | $8.67 | 13.54¢ |
| Nevada | $40.70 | $8.14 | 12.72¢ |
| New Hampshire | $88.45 | $17.69 | 27.64¢ |
| New Jersey | $78.75 | $15.75 | 24.61¢ |
| New Mexico | $52.83 | $10.57 | 16.51¢ |
| New York | $91.68 | $18.34 | 28.65¢ |
| North Carolina | $47.84 | $9.57 | 14.95¢ |
| North Dakota | $42.59 | $8.52 | 13.31¢ |
| Ohio | $62.02 | $12.40 | 19.38¢ |
| Oklahoma | $47.42 | $9.48 | 14.82¢ |
| Oregon | $50.94 | $10.19 | 15.92¢ |
| Pennsylvania | $69.66 | $13.93 | 21.77¢ |
| Rhode Island | $90.18 | $18.04 | 28.18¢ |
| South Carolina | $50.43 | $10.09 | 15.76¢ |
| South Dakota | $48.48 | $9.70 | 15.15¢ |
| Tennessee | $42.94 | $8.59 | 13.42¢ |
| Texas | $50.91 | $10.18 | 15.91¢ |
| Utah | $42.59 | $8.52 | 13.31¢ |
| Vermont | $76.29 | $15.26 | 23.84¢ |
| Virginia | $56.45 | $11.29 | 17.64¢ |
| Washington | $46.82 | $9.36 | 14.63¢ |
| West Virginia | $52.19 | $10.44 | 16.31¢ |
| Wisconsin | $62.11 | $12.42 | 19.41¢ |
| Wyoming | $46.18 | $9.24 | 14.43¢ |
How it works
The formula
cost = kWh × rate
saved = (all-night cost − timer cost) × months
Assumptions
- Full power while plugged in: most plain block heaters have no thermostat, so they draw their rating the whole time. Some heaters and kits have a thermostat that cycles the power; for those, enter the hours it's actually on, which a plug-in energy meter shows.
- Watts: about 400 W for a car frost-plug heater, 750 W for many pickups and diesels and 1,000 W for larger diesels (Zerostart ratings). Yours is printed on the cord.
- Timer: 2 hours, from Natural Resources Canada's advice that two hours is more than enough to warm the engine. SaskPower suggests about 4 hours on the coldest days.
Worked example: a car through a 4-month winter
400 W heater, 20 cold mornings a month, 4 months
- All night: 0.4 kW × 10 h × 20 = 80 kWh = $14.53 a month
- Timer: 0.4 kW × 2 h × 20 = 16 kWh = $2.91 a month
- Saved: ($14.53 − $2.91) × 4 = $46.49 a winter
Ways to cut the cost
- Use an outdoor-rated timer set to come on 2 hours before you leave; 4 on the coldest mornings.
- Plug in only when it's cold enough to need it; check your owner's manual for the temperature.
- Use a heavy outdoor extension cord rated for the heater's amps, and check the heater cord for cracks each fall.
- Unplug before you drive off. A cord-wrap reminder on the steering wheel helps.
Questions people ask
How much does it cost to run a block heater overnight?
A 400 W car block heater plugged in for 10 hours uses 4 kWh, about $0.73 a night at the U.S. average of 18.16¢ per kWh (EIA, August 2026). A 1,000 W diesel heater costs $1.82 a night.
How long should I plug in my block heater?
About two hours before you start the engine. Natural Resources Canada says two hours is more than enough to warm the engine and suggests a timer to switch it on; SaskPower suggests about four hours on the coldest days. Leaving it on all night uses far more power for little extra warmth.
How much does a block heater timer save?
For a 400 W heater used 20 mornings a month over a 4-month winter, switching from 10 hours a night to a 2-hour timer saves about $46.49 at the U.S. average rate: $32.56 in Nevada and $120.78 in Hawaii. SaskPower put the saving at about $65 a winter for an average household.
How many watts is a block heater?
Car frost-plug heaters are usually about 400 W; pickup and diesel heaters 750 to 1,000 W or more. The wattage is printed on the cord or the box. Most have no thermostat, so they draw their full rating all the time they're plugged in; a heater with a thermostat cycles and uses less.
At what temperature should I plug in my block heater?
A common rule in Canada is to plug in when it's about −15°C (5°F) or colder, and many diesel makers recommend it at higher temperatures. Check your owner's manual.