Electric or gas, instant or storage: Which water heater is right for your home?

SINGAPORE - Since April, household water heaters have been included in the National Environment Agency’s (NEA) Mandatory Energy Labelling Scheme, where ticks are used to indicate an appliance’s energy efficiency.

After a one-year grace period, from April 2026, water heaters on sale here must be registered with NEA and meet the requirements of the scheme. Models that fail to get at least a one-tick energy rating cannot be sold.

This is especially pertinent as water heaters are the third-most energy-intensive appliances used in households here after air-conditioners and refrigerators, accounting for some 10 per cent of an average household’s energy consumption. 

But among the different kinds of water heaters on the market here, which one should environmentally-minded home owners choose?

Experts told Simply Science that people should consider their usage patterns, the size of their homes, and other practical factors.

According to the NEA website, there are currently 203 types of water heaters in the market across four categories: electric instantaneous, electric storage, gas instantaneous and heat pump.

For energy efficiency, NEA recommends instantaneous water heaters over storage alternatives.

The agency also suggests that users with access to a gas network install a gas water heater instead of an electric storage heater.

Mr Alvin Ee, a research fellow at the National University of Singapore’s (NUS) Energy Studies Institute, explained that storage heaters inevitably lose heat to the environment due to the temperature difference between the heated water and its surroundings – a phenomenon known as standby heat loss.

“While insulation is typically installed to reduce heat loss, it does not eliminate it,” he said.

“By contrast, instantaneous gas water heaters avoid standby heat loss entirely, as water is heated only at the point of use rather than stored for prolonged periods.”

Additionally, while consumers prefer showers at 35 deg C to 40 deg C, electric storage water heaters are typically set to about 50 deg C or higher to prevent bacterial growth, Mr Ee said.

Maintaining stored water at such temperatures requires a significant amount of energy. To reach the desired temperature of around 35 deg C to 40 deg C, the hot water usually has to be mixed with unheated water.

“In practical terms, this means the system heats the water well above what is needed for comfort, incurs standby heat losses throughout the day, and then mixes the overheated water back down to a lower temperature,” said Mr Ee.

“This mismatch between required bathing temperature and required storage temperature contributes to the higher energy consumption associated with electric storage heaters,” he said.

By contrast, instantaneous systems – whether gas or electric – heat water only at the time of use, and only to the temperature needed, Mr Ee added.

A study commissioned by piped town gas provider City Energy

found that gas water heaters emit 0.19kg of carbon dioxide per kilowatt-hour, about half the amount produced by electric water heaters.

Conducted by Associate Professor Lee Siew Eang from the NUS College of Design and Engineering, the study found that annually, gas water heaters produce just 80kg of carbon per user, compared with the 400kg emitted by electric storage models. Piped town gas is a man-made fuel composed mainly of hydrogen and methane.

Mr Ee said that the high proportion of hydrogen in piped town gas lowers its carbon intensity – the amount of greenhouse gases emitted per unit of electricity produced – compared with electricity generated from natural gas.

This results in gas water heaters producing lower operational emissions than electric ones, he added

Instantaneous gas water heaters are now used in more than 210,000 households, or 14.3 per cent of all homes here, said City Energy.

While electric heat pump and solar thermal heaters have their advantages, they may not be suitable for most home owners here.

Electric heat pump water heaters – which work by transferring heat from the surrounding air rather than generating heat directly – can achieve significantly higher energy efficiencies unlike conventional electric gas heaters. However, they are usually bulkier and require larger, well-ventilated spaces, which limits their use in Housing Board flats or condominiums, said Mr Ee, noting that they also tend to have higher installation costs.

Solar thermal heaters, on the other hand, produce the lowest operational emissions as they rely primarily on sunlight.

However, their effectiveness is dependent on having roof space with adequate solar exposure, making them more suitable for landed properties, said Mr Ee.

When choosing a water heater, he advised households to consider criteria such as usage patterns – including the number of people using the heater and their bathing schedules – as well as long-term operating expenses, rather than just the upfront purchase price.

For most, instant electric heaters may be the most feasible option as they require less space than gas heaters, Mr Ee said.

But they may produce higher emissions due to the use of natural gas in Singapore’s electricity grid.

“Over time, the difference in emissions between gas and electric systems may narrow as manufacturers introduce more efficient heating technologies and improved insulation for electric storage heaters,” he said.

“Even so, under present grid conditions and typical usage patterns, gas water heaters continue to show comparatively lower carbon emissions than conventional electric storage models.”