Room Heater Electricity Consumption: Units Per Hour and Monthly Bill in India

Short answer: A room heater uses its wattage divided by 1,000 in units (kWh) every hour it runs at full power. An 800W quartz heater uses 0.8 units an hour, a 1200W fan heater 1.2 units, and a 2000W heater 2 units. At an example tariff of ₹8 per unit, a 2000W heater running 4 hours a night costs about ₹16 an hour, or about ₹1,920 a month. A thermostat that cuts power once the room is warm can bring that close to half. The type of heater (oil, fan, quartz, carbon) matters far less than its wattage, how many hours it runs and your state's slab tariff.

Every winter, the first electricity bill after the heater comes out is a shock for a lot of households. The good news is that you can predict that bill to within a few rupees before you switch the heater on. This guide shows the formula, gives ready-made tables for the common wattages sold in India, and covers the habits that actually cut the units.

The formula: how to calculate room heater units

One "unit" on an Indian electricity bill is one kilowatt-hour (kWh). That means 1,000 watts running for one hour.

Units used = (heater watts ÷ 1,000) × hours run

Cost = units used × your per-unit tariff

For example, a 1200W heater running for 3 hours uses 1.2 × 3 = 3.6 units. At ₹8 a unit that is ₹28.80.

Your tariff is printed on your bill. Most DISCOMs (BSES, Tata Power, MSEDCL, BESCOM, TANGEDCO and others) charge in slabs, so the rate per unit goes up as your monthly total goes up. Use the rate of the slab your bill usually falls into. The ₹8 figure in this article is only an example to make the maths easy. Replace it with your own rate.

Units per hour by heater wattage

These figures are at full power. They are pure arithmetic, so they hold for any brand.

Heater wattage	Typical type	Units per hour	Cost per hour at ₹8/unit
400W (one rod on)	Quartz/halogen, low setting	0.4	₹3.20
800W	2-rod quartz	0.8	₹6.40
950W	Carbon	0.95	₹7.60
1200W	Ceramic/fan heater	1.2	₹9.60
1500W	Fan heater, mid setting	1.5	₹12.00
2000W	Fan heater or oil-filled radiator	2.0	₹16.00
2500W	Large oil-filled radiator	2.5	₹20.00

The wattage is on the rating sticker on the back or base of the heater. It is also in the product listing. If the heater has two settings (for example 1000W/2000W), the units depend on which setting you use, not on the bigger number on the box.

Monthly room heater bill: worked examples

Most people run a heater for 3-6 hours a day in December and January. Here is the monthly bill for 30 days at 4 hours a day, still at an example ₹8 per unit.

Heater	Units per month (4 h/day)	Monthly cost at ₹8/unit
800W quartz	96	₹768
950W carbon	114	₹912
1200W fan heater	144	₹1,152
2000W fan or oil heater (full power)	240	₹1,920
2000W with thermostat cutting out half the time	about 120	about ₹960

Two things push the real number up or down.

1. The thermostat. Many fan and oil-filled heaters switch off once the room reaches the set temperature, then back on when it cools. In a small, closed room that cycling can cut the hours of real power draw a lot. In a big room with a draughty door, the heater may never cut out.
2. Your slab. 240 extra units in a month can move your whole bill into a higher slab. On some tariffs that raises the rate on every unit, not only the extra ones. Check the slab table on your DISCOM's website before you assume ₹8.

Does an oil heater use less electricity than a fan heater?

Not per hour. A 2000W oil-filled radiator and a 2000W fan heater both draw 2 units an hour while their element is on. The oil does not create extra heat.

The difference is in how they behave over a night:

• Oil-filled radiators warm the oil, which keeps giving off heat after the element switches off. With the thermostat set sensibly, the element can spend more of the night switched off. They are quiet and suit long, steady use in a bedroom.
• Fan heaters blow hot air fast. They warm a small room in minutes, but the room cools quickly once they stop. They suit short bursts, like 30 minutes before bed or while getting ready in the morning.
• Quartz, halogen and carbon heaters heat the person in front of them, not the air of the whole room. Their wattage is low (400-1000W), so they are the cheapest per hour if you sit close to them.

If you want the full trade-offs between radiant types, see our quartz vs halogen vs carbon heater comparison.

Which heater is cheapest to run for your room?

Your situation	Lowest-bill choice	Why
One person, sitting at a desk or on a sofa	800-950W quartz or carbon	Heats you directly, low watts
Small bedroom, 20-30 minutes before sleeping	1000-1200W fan heater	Warms the air fast, then you switch off
Bedroom running all night, closed room	Oil-filled radiator with thermostat	Holds heat, element cycles off
Large living room	2000W fan or oil heater on thermostat	Lower watts will just run non-stop

A low-watt heater that runs all night in a big room can cost more than a bigger heater that heats the room and then cuts out. Match the wattage to the room, not only to the price tag.

7 habits that cut the room heater's units

1. Close the door and windows. Heating a closed room is the single biggest saving.
2. Use the thermostat or the low setting. Running at 1000W instead of 2000W halves the units straight away.
3. Pre-heat, then switch off. Run a fan heater for 20-30 minutes before bed, then switch it off and use a blanket.
4. Sit close to radiant heaters. Quartz and carbon heaters lose most of their effect beyond a couple of metres.
5. Use a timer. Some heaters have one built in. A smart plug also works, and many show the real units used.
6. Don't run two heaters in one room. Rather close the room off properly.
7. Check your meter. Note the reading before and after one night of use. That is the true figure for your heater, your room and your weather.

Live room heater deals

These are live deals on RichDeals. We checked them at the time of writing, so confirm the price on the store page before you buy.

• Longway Blaze 800W quartz room heater with 2 heating rods: 0.8 units/hour at full power, 0.4 on one rod. A good fit for a single person.
• Venus Sun carbon room heater CH900, 950W, with tip-over switch: 0.95 units/hour, a radiant heater with a safety cut-off.
• Techking 1200W 2-in-1 ceramic heater fan: 1.2 units/hour, for quickly warming a small bedroom.
• Orient Electric Areva 2000W room heater: 2 units/hour at full power, for bigger rooms on a thermostat.

For more picks by room size and type, read our best room heaters in India winter guide, or browse every live discount on the offers page.