Background
There seems to be a lot of confusion surrounding the practise of switching off your geyser on a daily basis. Some people claim huge savings, while others warn that you might even consume more electricity, but the general consensus seems to be that you won’t really notice a saving.
Despite the fact that saving electricity is a big issue in South Africa at the moment, nobody seems to have data to back up their claims. Experts try to convince other by doing “thought experiments” or just ridiculing others ideas because they “know better.”
I’ve always been someone who believes the proof is in the pudding, thus I decided to do a real-life experiment to see if you can save electricity by switching your geyser on/off during the day.
Our Setup
We live in a house roughly 3 years old (ditto for the geyser); the geyser doesn’t have a blanket – probably the same setup as most modern houses. We’re a family of two (me and my wife) and shower/bath in the morning before going to work.
Experimental setup
To make sure I get an accurate reading of the energy consumption of the geyser, I connected an energy meter only to the geyser supply. I then measured the energy consumption on a weekly basis. On some weeks I left the geyser permanently on, while on other weeks I switched the geyser only on during the night. At first I manually switched the geyser off around midnight and switched it on again around 8:00 (just before going to work.) This wasn’t very practical, and on the second on/off week I forgot to switch it off for a day or two. On my current setup I’ve connected a timer switch that switches the geyser on at 3:30 AM and switches off at 6:45. The idea is to only heat the water for the morning shower, but I’ve also showered in the evening (around 18:00) and the water was still hot.
Results
I’m still busy gathering more data, but it’s already clear that you will save electricity by switching your geyser off for extended periods during the day.
| Week | On Duration | Energy used (KWh ) |
| 1 | Permanently on | 47.2 |
| 2 | On/off (on +-0:00 to 8:00) | 34.3 |
| 3 | Permanently on | 45.3 |
| 4 | *On/off (on +-23:00 to 8:00, skipped some days) | 41.2 |
| 5 | Permanently on | 47.3 |
| 6 | Permanently on | 51.7 |
| 7 | On/off (timer on 3:30 to 6:45) | 34.8 |
| 8 | On/off (timer on 3:30 to 6:45) | 37.3 |
* I’ve included week 4 to show the reduction in energy use, but I’m excluding it for the calculations below, as the geyser was neither permanently on, nor on/off on a daily basis.
| Permanently on | On/off | |
| Average energy consumption per week | 47.9 KWh | 35.5 KWh |
| Saving when switching geyser on/off | 25.9 % | |
| Cost per week (R0.44/KWh) | R21.07 | R15.61 |
| Cost per month (R0.44/KWh) | R90.85 | R67.10 |
Conclusion
If you use your geyser like a kettle (only boil water when you need it) instead of using it as an urn (always hot water available), you can save around a quarter of the energy used by your geyser. Of course you’ll have to take the needs of your family into account and it might not be plausible for big families that shower in the mornings and at night.
Also note that the geyser was switched off for extended periods every day – I doubt that you would gain much if you only switch the geyser off for an hour or two every day (alhough I’ll have to gather some data to back this statement… )