Water heating · Electricity units and running cost
A 2000 W geyser uses 2 electricity units during one full hour of active heating. Being switched on for an hour does not always mean it heats for the whole hour.
This guide separates heating time, hot-water demand and storage losses so you can estimate your own cost.
Electric geyser consumption = input watts × active heating hours ÷ 1000. One electricity unit is one kilowatt-hour (kWh). “Geyser,” “electric water heater” and “hot-water system” are regional terms; check the actual heater type before using the calculation.
Start with the element, not the tank size
Litres describe stored water. Watts describe electrical input. A 15-litre and a 30-litre tank can have the same element wattage but require different heating times. Record the model, input watts, storage capacity and your observed heating schedule.
Here the element heats for 45 minutes in total. If that happens every day for 30 days, use is 45 kWh. At an illustrative PKR 50/kWh, the energy charge is PKR 2250. This is a teaching example, not a current Pakistan tariff or a complete utility bill.
| Input | Daily units | 30-day units |
|---|---|---|
| 1500 W | 1.125 | 33.75 |
| 2000 W | 1.5 | 45 |
| 3000 W | 2.25 | 67.5 |
These are schedule comparisons, not proof that a lower-watt model uses less energy to heat the same water. A smaller element may simply run longer.
What happens after the thermostat cuts off?
A storage tank can cool and reheat even when nobody opens a tap. The US Department of Energy's archived storage-water-heater guide explains standby heat losses. Do not multiply the element rating by every hour that the wall switch is on unless it genuinely heats continuously.
For a practical log, record daily hot-water use, start and finish meter readings, heating schedule and unusual demand. A whole-home meter also includes other appliances, so its total difference is not automatically the geyser's consumption. Fixed-wired water heating needs appropriately installed metering, not an improvised plug adapter.
A second check: how much water is being heated?
Approximate heat delivered to the water = litres × temperature rise × 0.001163 kWh.
30 × 35 × 0.001163 = about 1.22 kWh of heat.
Original physics example using water density near 1 kg/litre and specific heat near 4.186 kJ/kg°C. It excludes tank, pipe and distribution losses. This is an energy balance, not an instruction to change a thermostat.
With an ideal 2 kW resistance element, that heat would take about 37 minutes. Real electrical use can be higher because losses occur. A heat-pump water heater needs a different input estimate because it transfers heat; do not apply a resistance-heater assumption to every hot-water system.
Use the wording and price on your own bill
- Pakistan: enter your applicable electricity unit rate; slabs, taxes and adjustments can change the full bill.
- US and Canada: use the local currency per kWh and check the unit's actual input rating and energy label.
- UK: an immersion heater heats water in a cylinder; count active element time and the relevant time-of-use rate.
- Australia: check whether the hot-water circuit uses a controlled-load tariff. Australian government guidance distinguishes storage, continuous-flow and heat-pump systems.
For the same 45 kWh example, a hypothetical USD 0.20/kWh gives USD 9; GBP 0.25 gives GBP 11.25; CAD 0.15 gives CAD 6.75; AUD 0.30 gives AUD 13.50. These are invented arithmetic inputs, not national average prices.
Manufacturer references: local and international
Check Nasgas's Pakistan catalogue and Rheem Australia's electric-water-heater range for model information. Confirm input, tank size, installation requirements and warranty in your market. These are reference links, not affiliate links or a tested ranking of brands.
Use your own electricity rate
Open the electricity bill and device estimator
Read how to calculate appliance electricity units and our methodology and limits. The device estimator calculates electricity; it does not turn LPG kilograms into an electricity bill.
Before buying a replacement
Compare the same hot-water demand, installation cost, energy tariff and expected annual input. First check leaks, unnecessary draw and the unit's maintenance guidance. A lower sticker wattage alone cannot establish a lower annual cost.
Prepared 2 November 2026. All numerical household scenarios are original hypothetical examples. Manufacturer pages support product identification, not independent performance testing. No universal daily consumption or savings percentage is claimed.
Choose the right calculation for your next question
Heating a room with electricity? Use the electric heater running-cost guide for 1000 W, 1500 W and 2000 W settings and thermostat cycling.
Buying LPG by the kilogram? The gas heater consumption guide converts a model's grams per hour into cylinder runtime and fuel cost.
For a household-wide check, use the seven-day energy worksheet before deciding which appliance to replace.
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