How much electricity does your geyser use?
Heating water is the biggest single use of electricity in most South African homes. Work out what your geyser costs each month, how long it takes to heat, and which changes actually save money.
Geyser electricity and cost calculator
For a standard electric geyser. Hot water use follows Eskom's household assumptions, and heat loss follows the South African standard for your geyser's age.
- About 272 litres of hot water a day for your household, needing 12,7 kWh to heat.
- Standing heat loss from the tank: about 1,4 kWh a day, 10% of the total. This is what a geyser blanket, pipe lagging or a timer can reduce.
- Your household uses more than one tankful a day, so the element reheats during the day. Staggering showers, or a larger geyser, avoids running out.
How long a geyser takes to heat up
Hours to heat a full tank from 20°C to 60°C. In practice the element rarely heats a whole tank from cold, but this is the worst case after heavy use or a long outage.
| Geyser | 2 kW element | 3 kW element | 4 kW element |
|---|---|---|---|
| 100 litres | 2,3 h | 1,6 h | 1,2 h |
| 150 litres | 3,5 h | 2,3 h | 1,7 h |
| 200 litres | 4,7 h | 3,1 h | 2,3 h |
| 250 litres | 5,8 h | 3,9 h | 2,9 h |
How the numbers are worked out
Heating one litre of water by 1°C takes 0.001163 kWh. The calculator multiplies that by your household's daily hot water, using Eskom's assumption of 80 litres per adult and 70% of that per child, and by the rise from 20°C incoming water to your thermostat setting.
It then adds the tank's standing loss: the heat that leaks away even when nobody uses hot water. South Africa's standard has limited this to 1.40 kWh a day for a 150 litre geyser since 2016, against 2.59 kWh before. Figures for other sizes are scaled from the 150 litre limit by tank surface area, which is our estimate.
Real use varies with shower length, winter inlet temperatures, pipe runs and the geyser's condition. Use your own tariff: municipal and Eskom prices differ, and many tariffs are stepped.
Geyser questions
How long does a 150 litre geyser take to heat up?
About 2,3 hours for a 3 kW element heating a full tank from 20°C to 60°C, and about 1,7 hours with a 4 kW element. A 200 litre geyser with a 3 kW element takes about 3,1 hours. Colder incoming water in winter takes longer.
How much electricity does a geyser use per day?
It depends mostly on how much hot water you use. Heating each litre from 20°C to 60°C takes about 0.047 kWh, so 200 litres a day needs about 9.3 kWh, plus the tank's standing heat loss. A 150 litre geyser made since 2016 may lose no more than 1.4 kWh a day under South Africa's efficiency standard.
Does switching off the geyser save electricity?
Only a little. While it is off, the tank still loses heat, just slightly more slowly because the water cools, and the element has to replace the heat once it is switched back on. The saving is limited to part of the daily standing loss, not the energy to heat the water you use. Eskom advises switching off when you are away for more than three days.
Is a geyser blanket worth it?
For older geysers, often yes. Eskom suggests an insulation blanket if the geyser is rated below R-24, together with lagging on the hot water pipes. Geysers installed since 2016 must meet a much stricter heat-loss limit, so the benefit is smaller.
What temperature should my geyser be set to?
Eskom recommends 60°C and says each 10°C reduction saves 3 to 5%. The World Health Organization recommends storing hot water at 60°C or above to control Legionella, so 60°C is a sensible setting for most homes.