Geyser electricity cost calculator: units, heating time • The Science 360

By Shounak Das · Updated November 2026 · 7 min read

How much electricity does a geyser use?

Most of it goes into the bath water itself. Warming a 20 litre bucket from 15 °C to 40 °C takes 0.58 units of heat. For a family of four taking one such bath each a day, a 25 litre, 2 kW geyser left on all day uses about 86 units a month, ₹604 at ₹7 a unit, and heats its tank from cold in about 40 minutes. About 16% of that is standing loss, the heat the tank leaks while it waits.

Choose the kind of heater, the baths a day, the litres and temperature of each, the cold water temperature, the geyser setting, and your tariff. The stage heats the tank and fills a bucket; the card compares a month on a storage geyser, an instant geyser, a heat pump and a solar heater. Defaults are examples as of November 2026 with sources below. For the longer explanation, read how much electricity a geyser uses.

Key results from the calculator

Four 20 litre bucket baths a day in winter (15 °C water in, 40 °C baths): 86 units and ₹604 a month on a 25 litre storage geyser, about ₹4.96 a bath.
Four 40 litre showers instead: 158 units and ₹1,109 a month. The litres matter more than anything else.
Switching the geyser on for 2 hours a day instead of leaving it on: 73 units, ₹91 a month less.
Same baths on a heat pump (COP 2.5) or a solar heater giving 70% of the heat: ₹238 and ₹181 a month.

Six examples, worked

Each example uses a 25 litre, 2 kW storage geyser set to 60 °C, cold water at 15 °C, baths at 40 °C, a standing loss of 0.465 kWh a day and ₹7 a unit unless it says otherwise. The button loads it.

A family of four, one bucket bath each

4 × 20 litres at 40 °C, geyser left on

Each bucket takes 20 × 4.184 × (40 − 15) = 2,092 kJ, or 0.581 units. Four a day, divided by 98% efficiency, is 2.37 units.

Keeping the tank at 60 °C all day loses 0.465 units more, so the day comes to 2.84 units: 86.3 a month and ₹604 at ₹7.

Units a month 86.3 Cost a month ₹604 A bath ₹4.96 Heat-up 40 minutes

Four showers of 40 litres each

twice the water of a bucket

A 40 litre shower holds twice the heat of a 20 litre bucket, 1.16 units. The standing loss stays the same.

The month rises to 158 units and ₹1,109. Each shower uses 22.2 litres of 60 °C water, so the 25 litre tank manages 1.1 showers before it must reheat.

Units a month 158 Cost a month ₹1,109 A shower ₹9.12 Showers per tank 1.1

Switching the geyser on only before baths

kept hot 2 hours a day

The heat in the baths does not change. The standing loss falls from 0.465 to 0.039 units a day.

That saves 13 units, ₹91 a month: worth doing, but smaller than cutting the litres.

Units a month 73.3 Cost a month ₹513 Saved a month ₹91 Standing loss 0.039 kWh a day

A 3 litre, 3 kW instant geyser

no tank to keep hot

With no standing loss, the same four buckets take 72.1 units, ₹505 a month.

But 3 kW warms only about 1.7 litres a minute by 25 °C, so each 20 litre bucket takes 11.9 minutes. That suits a bucket bath better than a shower.

Units a month 72.1 Cost a month ₹505 Bucket takes 11.9 min Flow at 40 °C 1.7 L/min

A heat pump water heater

COP 2.5, 0.5 kW input

A heat pump moves heat from the room air into the water. At a COP of 2.5, each unit of electricity puts 2.5 units of heat in the tank.

The same baths and standing loss take 33.9 units, ₹238 a month. The purchase price is not counted.

Units a month 33.9 Cost a month ₹238 Saved vs storage ₹366 Heat-up 63 minutes

A solar water heater with electric backup

the sun gives 70% of the heat (example)

If the sun supplies 70% of the heat over the month, the backup element supplies the rest: 25.9 units, ₹181.

The share is an example. It is higher in a sunny south Indian winter and lower in foggy north Indian weeks; type your own.

Units a month 25.9 Cost a month ₹181 Saved vs storage ₹423 Sun’s share 70%

Heat in one bath, and a month of four a day on a 25 litre storage geyser

Water per bath	Heat at 40 °C from 15 °C	Cost a bath at ₹7	A month, 4 a day	Same in summer (25 °C in)
10 litres	0.29 kWh	₹2.08	50 units, ₹352	33 units, ₹229
15 litres	0.44 kWh	₹3.11	68 units, ₹478	43 units, ₹304
20 litres	0.58 kWh	₹4.15	86 units, ₹604	54 units, ₹380
30 litres	0.87 kWh	₹6.23	122 units, ₹857	76 units, ₹532
40 litres	1.16 kWh	₹8.30	158 units, ₹1,109	98 units, ₹683
60 litres	1.74 kWh	₹12.45	231 units, ₹1,614	141 units, ₹986

Includes a standing loss of 0.465 kWh a day at a 45 °C difference, scaled to the difference between the 60 °C setting and the cold water, with the geyser left on. Multiply units by your price per unit.

How the calculator works

The heat in each bath is litres × 4.184 kJ per kg per °C × (bath temperature − cold water temperature), divided by 3,600 to give units (kWh). A litre of water is taken as 1 kg. Mixing hot and cold water does not change the total, so the geyser setting does not change this part.

The geyser setting decides how many litres of tank water each bath uses: bath litres × (bath − cold) ÷ (setting − cold). It also sets the standing loss, the heat lost through the insulation. BEE’s star label gives this loss over 24 hours with the tank 45 °C above the room; the calculator scales it to your setting (taking the room as the cold water temperature) and the hours the geyser is kept hot.

Electricity a day: storage geyser = bath heat ÷ efficiency + standing loss; instant = bath heat ÷ efficiency; heat pump = (bath heat + standing loss) ÷ COP; solar = (1 − solar share) × the storage figure. A month is a day × 365 ÷ 12. Heating time is the heat for a full tank divided by the heater kW (times efficiency, or times COP for a heat pump).

What the model leaves out

Pipe losses: hot water left in the pipe after a bath cools there; long pipe runs add to the bill.
Cooling while switched off: a tank switched off still loses some heat as it cools, which the reheat then replaces; the calculator counts loss only while it is kept hot.
Purchase and fitting: prices of heat pumps and solar heaters, and their life, are not included.
Fixed charges and taxes: only the energy charge per unit is counted.

Common misconceptions

"A higher wattage geyser uses more electricity." It heats faster, but the heat the water needs is the same. A 3 kW heater does the job in two thirds of the time a 2 kW one takes.

"Setting the geyser hotter costs much more." Hotter tank water is mixed with more cold water for the same bath. Only the standing loss rises, a small part of the bill.

"Leaving the geyser on all day doubles the bill." For a well insulated 4-star 25 litre tank, a whole day of standing loss is under half a unit, less than one bucket bath.

Frequently asked questions

How much electricity does a geyser use per day?

For four 20 litre bucket baths at 40 °C from 15 °C water, a 25 litre, 2 kW geyser left on all day uses about 2.8 units a day: 2.4 for the water and 0.47 of standing loss. That is about 86 units, ₹604 a month at ₹7.

How long does a 25 litre geyser take to heat?

About 40 minutes for a 2 kW geyser heating 25 litres from 15 °C to 60 °C. The water needs 25 × 4.184 × 45 = 4,707 kJ, 1.31 units, and 2 kW delivers that in about two thirds of an hour.

Should I switch off the geyser after use?

It helps a little. A 4-star 25 litre geyser kept at 60 °C all day loses about 0.47 units a day; switching it on only 2 hours a day saves about ₹91 a month at ₹7. Using fewer litres saves more.

Is an instant geyser cheaper than a storage geyser?

It saves the standing loss, about ₹99 a month in our example, because it has no tank to keep hot. But a 3 kW instant geyser warms only about 1.7 litres a minute to 40 °C, so it suits bucket baths more than showers.

How much does a solar water heater save?

MNRE says a 100 litre a day solar water heater may save about 1,500 units of electricity a year. The real saving depends on how much hot water you use and how sunny your winters are.