Hi all.

I need some clarification on the electricity consumption for water heater at my condo. Of recent, I noticed from the TNB app, my daily usage bill seems to keep increasing everyday. It is worrying, eventho my usage is pretty much the same. I have little appliances in the house.

One of the possible culprit that I suspect is the water heater. I don't know how to describe the type but my unit uses (I believe) the central water heating - where I have to turn on the switch outside of the toilet to get the hot water.

Now, my question is:

1. Do I turn ON only when I'm using it? Turn off after OR it is fine to leave it on (only turn off when away from home very long). Because I read somewhere, I can just leave it ON, because it only consume electricity when the shower is ON - when the water run thru the heating rod or something.

2. How do I figure out which type the condo is using? How do I check?

3. If turn off and on, will it use more electricity since it requires the water to be heated first?


I strongly believe other usage not effecting the bill - cause I only use 1 aircond with 1 hp at night for 7 hours. The rest is just fan, charging gadget, LED lights and fridge. Kitchen appliances rarely use.


Please help for those who knows this matter. Thanks a lot!

Check first what type of water heater you are using. Instant water heater or tank type.

How do I check that? I'm not exactly sure.

This type is it? The one that hide above your ceiling

https://www.joven-electric.com/my/products/...jsh-series.html

climb up open the ceiling panel, see what brand and model the tank

turn off when not using. Turn on 5 min before shower will do. Check the seal of your refrigerator, water heater won't suddenly consume large amount of electricity. Maybe be is also due to weather is hot, so AC work extra to cool down the room.

The tank type has a cutoff, if you leave it on all the time it only turns on the heating when the temperature drops below the set point.

I have a screenshot of mine from Home Assistant that should illustrate what I mean, I leave mine on all the time.

BTW mine uses a lot of energy because its a 90L tank, which is way overkill ... last time listened to the contractor who recommended this size but I think for my double storey with 3 baths even 30L would have been enough.

I have to check first and climb the ceiling.

Ok I will do that when I'm home

But mine is a condo. So I'm not exactly sure. Shouldn't mine uses the condo's tank?

If you got a switch it should mean you have a small tank in the ceiling of the bath.

Same principle just smaller size.

Based on your reply, meaning mine is tankless heater? And this suggest that I have to turn off when not in use to save electricity consumption?

Let me know if my understanding is wrong.

Just take a photo of your shower area. It will show whether you have a instant heater or a tank type. Funny that you cannot differentiate between the two.

Sorry that I don’t know. Not well versed in this matter. Here’s the photo of shower area. There’s no water heater unit


Attached thumbnail(s)

I have checked and confirmed that it is this type as per your link. What’s your advice?

Tank water heater will consume more. It heats up the water when the temp is below the threshold.

Instant only consume during first 10 mins. After that, very little.

After my WH died, I gave up replacing it. Now just bath using cold water. Nice and cooling. Of course, don't use the AC immediately. Wait like 30 mins then only turn on the AC.

You need to turn the switch OFF when not using

As the unit aged it will spoil fast so to prolong its lifetime best to switch off

Mine last more than 15 years and when I told the shop they say it’s impressive dy. Most start to spoilt at 6th year onwards

Ok got it. Thanks

Ok understand now. I should turn on only when showering. The reason why I turn on all the time was because someone told me it is more energy efficient and turn on/off all the time would spoil it.

I guess I got a wrong advice. Thanks for your input

Perhaps you can use the tank type until it finally konk out and change to instant water heater which to me is more practical, uses electricity only when water goes through the magnetic switch and hot water flows almost instantly. I guess the tank type is more when you need hot water for whole house such as kitchen also.

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