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Geyser timers and smart geyser controllers: do they save electricity?

In most South African homes, the geyser is the biggest single user of electricity. Heating water from cold and keeping it hot all day can easily use a third to half of a home's electricity. Measure first, then schedule the geyser.

Understand your units

Your bill or prepaid slip is in kilowatt-hours (kWh), also called units.

• 1 kWh is 1 000 W for one hour.
• A 3 000 W geyser element uses 1 kWh in 20 minutes.
• Energy (kWh) = power (kW) × hours.
• Cost = energy × price per kWh.

To find your price per unit, divide what you paid for electricity by the units you bought. Many tariffs are stepped, so later units in the month cost more.

Measure before you change anything

A smart plug with energy monitoring measures one plug-in appliance at a time. Leave it for a few days on:

• the fridge and freezer (does it run almost all the time?);
• the TV corner on standby;
• a second fridge in the garage.

Also look at what the home uses overnight. Small loads that never stop add up.

A whole-home monitor clamps onto the cables in the distribution board. Fitting it is a job for a registered electrician. Some prepaid meters and inverters already measure whole-home use, so check before you buy.

Geyser habits first

• Have a plumber or electrician set the thermostat to about 60 °C. That is hot enough to control bacteria without wasting heat.
• Fit a geyser blanket and insulate the first metre or two of hot pipe.
• Use less hot water: shorter showers and a low-flow shower head.

Timers and smart controllers

A geyser timer lets the geyser heat only before you need hot water, for example from 04:30 to 06:30 and from 16:00 to 18:00. A smart geyser controller does the same from an app, and many also show the water temperature and how much electricity the geyser used.

Both are wired into the geyser's 230 V supply. Fitting one is electrical installation work for a registered electrician, who issues a certificate of compliance. After that, the schedule is yours to set and adjust.

Never put a geyser on a smart plug, an extension lead or a plug-in timer. A geyser is not plugged in, and its current is far too high.

If you have solar

Heat the geyser in the middle of the day, when the panels produce the most. Run the pool pump, dishwasher and washing machine then too.

Your inverter's app shows the battery level, solar production and home use, and lets you set when the battery charges and how much reserve it keeps for an outage. Do not change settings that the installer has locked, and do not run extension leads from the inverter's output.

Other loads worth scheduling

• Pool pump: on a timer, with shorter hours in winter.
• Electric blankets and heaters: short warm-up runs with a fixed switch-off time.
• TV corner and home office: off at night.

When the power comes back

After an outage, everything starts at once, which can trip breakers, and surges can damage electronics.

• Switch off heaters, the oven and the kettle during an outage.
• Set each smart plug's "power-on behaviour" in the app: off for heaters, on for the fridge.
• Stagger heavy loads. For example, have the pool pump wait ten minutes.
• Put sensitive electronics on surge-protected plugs.

This guide is based on Chapter 5 of Automating Your Home.