Basically how a storage water heater functions is that there are
i. a thermostat internally that automatically turns on and off the heating element to keep the water in the tank at a certain temperature range, on average it should be between 65°C (where below this temperature, the thermostat will turn on the heating) to 75°C (where above the temperature, the thermostat will turn off the heating), and
ii. an insulation layer around the tank to minimize heat loss (hot water from cooling down drastically), just like a ThermoFlask.


In my opinion,
a. keeping it on the whole time - I don't think it is more energy efficient, as logically you are using more energy (electrical supply) than what u consume (for showers).
b. turning it on/off all the time - I don't think it will cause damage to it. Same logic as u turning an electric kettle on and off all the time, it doesn't shorten its lifespan.
c. turning it off when not in use - as per what knwong has mentioned, technically all devices, when switched on for a longer period of time, will shorten its lifespan. But storage water heaters should be built to last, even if it is turned on all the time, at least until their warranty period end.


My suggestion is, if u want it to be more energy efficient, u can turn it off when it is not in use. U just have to bear the hassle of waiting a bit after turning the switch on before shower. But I wouldn't go as far as to say u HAVE to turn it off if it is not in use. Some storage water heaters supply hot water to basins (eg. like restaurant kitchens and hotel lobby bathrooms), where hot water are been used intermittently throughout the day. These storage water heaters don't get turned off at all, yet they don't get spoilt within a year, correct?

Hence, it is really up to u whether u want to turn it on / off or not on a daily basis, or just keeping it on all the time, but of course turn it off when u r away for a long period (eg. holiday).


Lastly, heat insulation in these storage water heaters are not that lousy that will cause your electric bill to skyrocket. If u want to test it out, the easiest way is to monitor your TNB app (provided u have a TNB smart meter), refer to your daily electrical usage, and do a test by monitoring:
a. 1 day without storage water heater usage at all (switch turned off the whole day),
b. another day with storage water heater switch kept on the whole time, and shower with hot water as usual, and
c. another day with storage water heater switch only turned on when u shower, and turn off after shower.

Use other electrical appliances in your house as per usual, and try to keep it consistent these 3 days. See if there is any significant differences in electrical usage these 3 days, and make your conclusion accordingly.



This post has been edited by Selene Yeo: Jul 1 2025, 09:27 PM

My experience with my condo storage tank (Rheem 30L tank) and my smart meter daily electricity consumption monitor:

Turn on 15 mins to heat up in morning than off = able to tahan enough heat in tank, got sufficient hot water for two people to shower at lukewarm temperature water at night. Electricity consumption not significant enough to notice.

One fine day turn on at morning at usual time, then forgot to turn off until return at night = suddenly that day electricity shoot up extra 6kWh of electricity used