Published:  2015-09-14 Views:  1102
Author:  JFK
Published in:  Technical/Tegnies
Show Me The Money! Geyser Electricity Costs Savings?

People understand Rands and cents, and not kWh (kilo-watt-hours). So that’s what I’ll show you here.

The biggest energy hungry vampires in your home are all the appliances that have a heating element; your stove, geyser, kettle, hair dryer, dishwasher, tumble dryer, toaster, and heaters.  

By now, most people know that your geyser is generally the single biggest energy culprit in your house. We also know that we can reduce our hot water costs by lowering the thermostat setting, adding insulation to the geyser and piping, using less hot water and switching the geyser off during the day, right?

Now let me show you something really interesting!

Fun Fact: 65˚C is the optimal water temperature heat setting. Under 55˚C bacteria can grow (bad) and above 65˚C you increase the risk of calcification in your geyser and water pipes (also bad).

For this exercise, let’s assume you pay an average of a R1000 for 625 electricity units. That’s R1.60 per unit (kWh). Starting with a cold geyser at room temperature (ie. 20˚C).

If your (150Liter) geyser is cold (20˚C), its thermostat set to 65˚C for hot water with a standard 3kW (3000Watt) element. To get your water up to 65˚C (when the thermostat switches the geyser off), it takes 2.6 hours and uses 7.86kWh (there is a scientific formula to calculate this).  

That means you pay R12.57 for this 2.6 hours of electricity;

R87.99 for the week

R369.56 for the month and

R4,434.70 for the year…

and that’s just your geyser ON (from cold water to hot water) for ONLY 2.6 hours!

How long is your geyser on every day?

It’s a popular statement that switching your geyser OFF saves electricity, right?

So does it actually make a difference or not? And installing a timer or manually switching off your geyser at the DB board has the same identical result; one method is just automatic and the other manual (a timer is just more convenient because it has its own ‘memory’ so you don’t have to remember).

A geyser thermostat is purely an on/off switch; it’s a dumb device (meaning it has no intelligence). When the water temperature reaches 65˚C, the switch opens up and your geyser is OFF. Now the water slowly starts to cool down (about 10˚ over 24 hours – from previous studies) and eventually the thermostat switches on again.

Remember I said that your thermostat is not intelligent; it does not allow MORE power (volts and amps) through if the water is colder or LESS power (volts and amps) if the water is fairly warm. Every time the thermostat switches ON, it uses the FULL 3000Watt element at FULL power to heat the water. The actual water temperature will determine HOW LONG the element will stay FULLY ON till it reaches 65˚C again.


If you leave your geyser ON all day, the thermostat will switch on and off for about 2 minutes every two hours to keep the water at 65˚C (from previous studies); that’s 24 minutes in 24 hours; equals 0.4 hours.

Cost of R1.92 per day

R56.45 per month

and R677.38 per year


If you switch the geyser OFF for 12 hours a day, the water will cool down and when you switch back on; the duration it takes for the water to reheat from 60˚C to 65˚C is 0.3 hours (from calculation).

Cost of R1.44 per day

R42.34 per month

and R508.03 per year

So you tell me… which option above uses more electricity?

In order to get a baseline, the calculations above are based on a new perfect installation, and no warm water being used during a 24 hour period. In practise these figures would obviously be quite different for each installation.

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