Water Heater Electricity Cost: Storage vs Instant Heater
Your household
Instant heater
It heats water only while the shower runs, at its full rated power.
Assumption: 3.3 kW. Check the rating plate. Runs 30 min a day for your household.
Storage heater
It heats a tank, then the thermostat switches it off. Heat leaks from the tank while it stays on.
Assumption: 2.5 kW. Check the rating plate.
Assumption: 45 min. Roughly the time from switching on until the indicator light goes off, plus any top-up heating later.
Monthly running cost compared
- Instant heater 49.5 kWhS$15.43
- Storage heater 56.3 kWhS$17.53
An instant heater draws more power at once but only while you shower; a storage heater uses less power for longer and loses some heat if left on. Switching a storage heater off after use usually saves the most.
Instant heater: cost per month
S$15.43
- Per day
- S$0.51
- Per year
- S$185
- Per person per month
- S$5.14
- Storage heater instead
- S$17.53
Your instant heater is S$2.10 a month cheaper to run.
How this works
An instant (tankless) heater runs at its full rated power only while a shower is on, so its energy is rated kW × total shower time per day. The default 3.3 kW is an assumption; check the rating plate on your unit.
A storage heater heats a tank until its thermostat switches off, so its energy is rated kW × the time it spends heating each day (an assumed 45 minutes at 2.5 kW by default). If it is left on 24 hours, an assumed standby loss of 1 kWh a day is added for the heat that leaks from the tank.
Monthly cost = kWh per day × 30 days × SP Group's regulated tariff of 31.16 cents per kWh including GST (28.59 cents before GST) for 1 October to 31 December 2026.
FAQs
How much electricity does a water heater use in Singapore?
For 3 people taking 10-minute showers, a 3.3 kW instant heater uses about 1.65 kWh a day (49.5 kWh a month), which costs about S$15.43 a month at the October to December 2026 tariff.
Is a storage or instant water heater cheaper to run?
With the defaults here, an instant heater costs about S$15.43 a month and a 2.5 kW storage heater heating for 45 minutes a day about S$17.53. Leaving the storage heater on 24 hours adds an assumed 1 kWh a day of standby loss, taking it to about S$26.88.
Should I switch off my storage water heater?
Usually yes. Keeping the tank hot all day adds standby losses, about S$9.35 a month at an assumed 1 kWh a day and 31.16 cents per kWh. Switching on 30 to 60 minutes before showers avoids most of it.