Heater Electricity Cost Calculator (Hot-Water Mat, Heater, Humidifier)
See how much your monthly electricity bill goes up when you turn on a hot-water mat, carbon mat, electric blanket, electric heater or humidifier. The calculator works out the bill "before" and "after" switching it on, using KEPCO (한국전력) residential low-voltage progressive rates (누진제), and shows the difference.
Show how it is calculated
1. Electricity the device uses: power (W) × hours per day × days of use × share of time on ÷ 1,000 = extra monthly usage (kWh). A 200W carbon mat used 8 hours a day for 30 days is 200 × 8 × 30 ÷ 1,000 = 48kWh.
2. Bill before turning it on: if current usage is 300kWh, base charge 1,600 won (201–400kWh tier) + energy charge (200kWh × 120.0 won + 100kWh × 214.6 won = 45,460 won) + climate and environment charge (기후환경요금) (300kWh × 9.0 won = 2,700 won) = 49,760 won. Adding 10% value-added tax (부가가치세) (4,976 won) and the 2.7% Electric Power Industry Fund (전력산업기반기금) (1,344 won) gives 56,080 won.
3. Bill after turning it on: the same method at 348kWh gives a base charge of 1,600 won + energy charge 55,760.8 won + climate and environment charge 3,132 won = 60,493 won; adding VAT of 6,049 won and the fund of 1,633 won gives 68,175 won.
4. Difference: 68,175 won − 56,080 won = 12,095 won is the extra monthly bill caused by this device. The electricity charge subtotal, VAT and fund are each rounded to the nearest won.
How to use
First choose the device type, and an example value is filled into the power consumption box. This value is not an official standard; it is an example within the range commonly seen on products for sale (hot-water mat 200–400W, carbon mat 150–300W, electric blanket/pad 100–300W, electric heater 1,000–2,000W, heated humidifier 200–500W, ultrasonic humidifier 20–50W). Replacing it with the power consumption written on your own product's label or manual makes the result much more accurate. For a device not on the list, choose "Enter manually" and type its power consumption.
Next, enter how many hours a day and how many days a month you use it. The most important box is "Your home's current monthly electricity use". Residential electricity uses a progressive rate system (누진제) in which the price per kWh rises the more you use, so the same device adds very different amounts depending on how much electricity the home already uses. Enter the "current month usage" on your bill or the usage shown in the KEPCO ON (한전ON) app.
The result shows the extra monthly bill, the extra usage, whether you move into a different tier, and a comparison table of the cost for each device type under the same conditions.
Rates used now
These are the residential (low-voltage) rates posted in the KEPCO Cyber Branch (한국전력 사이버지점) rate table. The posted table's effective date is November 9, 2023 (for residential low-voltage the values are the same as May 16, 2023), and when checked on October 16, 2026 this table was still posted as the current one. A KEPCO announcement reported on September 21, 2026 said the base charge, energy charge and climate and environment charge stay unchanged for the fourth quarter of 2026 (October–December).
| Monthly usage (Jan–Jun, Sep–Dec) | Base charge | Energy charge |
|---|---|---|
| 200kWh or less | 910 won | 120.0 won per kWh |
| 201–400kWh | 1,600 won | 214.6 won per kWh |
| Over 400kWh | 7,300 won | 307.3 won per kWh |
- Winter super-user rate: if you use more than 1,000kWh in a month between December 1 and the end of February, the part above that is 736.2 won per kWh. Choose Dec–Feb in "Month to calculate" to apply it.
- Climate and environment charge (기후환경요금): 9.0 won per kWh used (applied since January 2023, per KEPCO guidance).
- Value-added tax (부가가치세): 10% of the electricity charge subtotal.
- Electric Power Industry Fund (전력산업기반기금): 27/1,000 (2.7%) of the electricity charge subtotal, set by Article 36 of the Enforcement Decree of the Electric Utility Act (전기사업법 시행령).
- Fuel cost adjustment charge (연료비조정요금): not included. We could not confirm the fourth-quarter 2026 rate (reported in the press as a continued +5 won per kWh) on an official KEPCO page, so it is left out. If it applies, about 5.6 won (including VAT and fund) is added for each additional kWh.
- Summer (July–August) has different tier boundaries of 300kWh and 450kWh, so this calculator does not cover it. Welfare discounts, large-family discounts, and the extra reduction for welfare-discount households are not reflected either.
Why the same device costs different amounts in different homes
A 200W carbon mat used 8 hours a day for 30 days adds the same 48kWh in any home. But the extra cost changes with the home's existing usage, as follows.
- Home currently using 150kWh: it becomes 198kWh and stays within tier 1. The extra cost is about 6,978 won.
- Home currently using 300kWh: it becomes 348kWh and the increase stays within tier 2. About 12,095 won.
- Home currently using 380kWh: it becomes 428kWh and moves into tier 3, and the base charge also changes from 1,600 won to 7,300 won. About 21,445 won.
The same 48kWh differs by more than three times. A home whose usage is just under a tier boundary (200kWh, 400kWh) can be pushed into the next tier by even one small heater, so try changing "current usage" in the calculator.
What is the difference between hot-water mats, carbon mats and electric blankets?
A hot-water mat heats water in a main unit and circulates it through hoses inside the mat, while carbon mats (탄소매트) and electric blankets/pads (전기요·전기장판) produce heat directly from heating wires or carbon heating elements inside the mat. The electricity bill depends on power consumption and hours on, not on the type name. The same watts for the same hours cost the same.
However, a hot-water mat has a main unit that heats water, so many products list a higher power consumption than wire-based mats, and with a thermostat the actual power used may be lower than the listed value. So rather than saying one is cheaper, it is more accurate to enter the power consumption on your own product's label and the hours you actually use it. The comparison table under the result uses example power values, so it is for reference only.
How much do electric heaters and humidifiers cost?
Many electric heaters draw more than 1,000W, so they affect the bill far more than mats. A 1,500W heater used 3 hours a day for 30 days adds 135kWh, and for a home currently using 300kWh that moves into tier 3 and adds about 44,100 won a month. It suits short use close to a person rather than heating a whole room.
Humidifiers differ greatly by type. A heated type boils water to release steam and uses several hundred watts, while an ultrasonic type turns water into tiny droplets by vibration and uses a few tens of watts. For the same 8 hours a day for 30 days, a 300W heated type uses 72kWh and a 30W ultrasonic type uses 7.2kWh, a tenfold difference.
Safety rules to read before use
According to a summary by the Ministry of the Interior and Safety (행정안전부) based on National Fire Agency (소방청) National Fire Information System data, electric heater and electric blanket fires over the three years 2021–2023 numbered 1,403, with 21 deaths and 142 injuries. They were most frequent in December and January; 49% of electric heater fires involved flammable items placed close by, and 83% of electric blanket fires were due to careless use of the device.
- Before use, check that the plug, cord and heating wire are not loose or worn.
- Turn the power off when you go out or leave the spot for a long time, and after you finish. Stopping it periodically with a timer also helps.
- Do not leave easily ignited items such as paper, clothes or towels near an electric heater.
- Keep electric blankets from being folded or pressed under heavy objects, and do not use them under layers of bedding.
- Even at a low temperature, long contact with an electric mat can cause low-temperature burns. The government guidance is to put a blanket on top, reduce high-temperature use, and use an automatic shut-off timer when sleeping. When buying, check for the KC certification mark.
Basis of calculation
Reference year: 2026 (rate table checked 2026-10-16)
- KEPCO Cyber Branch (한국전력 사이버지점) Korean electricity rate table (residential power, low voltage, effective November 9, 2023) — checked 2026-10-16
- KEPCO Cyber Branch main electricity rate systems (climate and environment charge 9.0 won/kWh, from January 2023) — checked 2026-10-16
- KEPCO Electricity Supply Terms (한국전력 전기공급약관) Article 67 (the charge is the sum of the base charge, energy charge, climate and environment charge and fuel cost adjustment charge) — checked 2026-10-16
- National Law Information Center (국가법령정보센터) "Enforcement Decree of the Electric Utility Act (전기사업법 시행령)" Article 36 (the contribution is 27/1,000 of the electricity charge) — checked 2026-10-16
- Policy Briefing (정책브리핑) (Ministry of the Interior and Safety, 2024-11-27) electric heater and electric blanket fire statistics (National Fire Information Center and National Fire Agency data), and Policy Briefing (Ministry of Trade, Industry and Energy (산업통상자원부), 2023-11-06) on preventing low-temperature burns from electric mats — checked 2026-10-16
Not included: fuel cost adjustment charge (official rate not confirmed), summer rates, welfare and large-family discounts. We could not find KEPCO's rounding rule for bills on an official page, so we rounded to the nearest won, and the actual bill may differ by a few tens of won. If the rate table changes, we will check it again and update.
Common mistakes
- Entering the usage of the month the heater was on as "current usage": that usage already includes the heater, so it would be added twice. Enter the usage from a month before you turned it on.
- Entering the number from an apartment maintenance-fee bill: in apartments, how the bill is calculated can differ depending on the complex's contract type. This calculator is based on residential low-voltage service contracted directly with KEPCO.
- Calculating only with maximum power consumption: mats and heaters with a thermostat use less once they reach the set temperature. Change "share of time it is actually on" to 70 or 50 to see the range.
Frequently asked questions
Which costs less to run, a hot-water mat or a carbon mat?
Power consumption and hours of use decide it, not the type. At 8 hours a day, 30 days and 300kWh current usage, a 300W hot-water mat adds about 18,143 won and a 200W carbon mat about 12,095 won. The same watts cost the same, so enter the power consumption on your own product's label to compare.
Can the progressive rate suddenly raise the bill a lot?
Yes. For Jan–Jun and Sep–Dec, the price per kWh rises from 120.0 won to 214.6 won to 307.3 won at 200kWh and 400kWh, and above 400kWh the base charge also goes from 1,600 won to 7,300 won. A home that used 380kWh and adds 48kWh pays about 21,445 won more, over three times what a home that used 150kWh pays (about 6,978 won).
Is it OK to fall asleep with an electric heater on?
We do not recommend it. In data from the Ministry of the Interior and Safety and the National Fire Agency, many electric heater fires came from flammable items placed close by or from leaving the device unattended. Turn it off when you leave or sleep, and keep bedding, clothes and paper away from it.
Why is the fuel cost adjustment charge left out?
We could not confirm the fourth-quarter 2026 rate on an official KEPCO page, so it is not in the calculation. If +5 won per kWh continues as the press reported, about 5.6 won (including VAT and fund) is added for each additional kWh of usage.
How much does the electricity cost differ between heated and ultrasonic humidifiers?
An example 300W heated type uses 72kWh in 8 hours a day over 30 days, and a 30W ultrasonic type uses 7.2kWh. For a home currently using 300kWh, that adds about 18,143 won and about 1,814 won respectively.
This is a reference calculation; official guidance from the relevant institution takes precedence. For the exact amount billed, check with KEPCO (dial 123 with no area code) or KEPCO ON (한전ON).
Related pages
- Winter heating picks — selection criteria (KC certification, overheat protection, low-temperature burns) and a list of heating products
- Pyeong calculator — check a room's area in ㎡ and pyeong