Instant water heater vs storage: side by side
The table draws on NEA's Resource Efficiency Guide for New Home Owners and what the Energy Label shows for each type.
| Point | Instant water heater | Storage water heater |
|---|---|---|
| How it heats | Heats water as it flows through the unit | Heats a stored amount of water and keeps it hot |
| Energy use while idle | Only uses energy while water flows | Keeps using energy to keep water hot while switched on |
| Energy Label shows | Ticks, annual energy cost and consumption, type, rated input power in kW | The same, plus capacity in litres |
| Typical fit to consider | Often weighed for one bathroom; ask a plumber if two showers may run at once | Often weighed for several bathrooms or a bathtub; choose a capacity that meets your needs |
| Installation work | Ask what the quote covers, such as removing the old unit | Ask what the quote covers and where the unit will go |
If your current heater needs fixing or you plan to switch types, look up companies that do water heater repair and installation.
Is an instant or storage water heater cheaper to run?
NEA's Resource Efficiency Guide for New Home Owners gives clear advice: choose an instantaneous water heater over a storage water heater, as it is more energy efficient. If you prefer a storage water heater, NEA says to choose a capacity that meets your needs.
The difference comes from how each type uses power. According to the NEA guide, storage water heaters continue to use energy to heat water when they are left switched on. Instantaneous water heaters only use energy to heat water when it flows through the unit. So storage heater electricity use is not limited to the minutes you spend in the shower.
Reading the Energy Label
NEA's Energy Label rates efficiency in ticks: 1 (Low), 2 (Fair), 3 (Good), 4 (Very Good) and 5 (Excellent). On a water heater, the label also shows:
- the annual energy cost and annual energy consumption
- the type: electric instantaneous, gas instantaneous, electric storage or heat pump
- the rated input power in kW
- the capacity in litres, for storage heaters
The annual figures use fixed assumptions set by NEA: electricity at 27 cents per kWh and 3 showers a day. These assumptions let you compare models. They are not the tariff you pay.
Your real running cost will differ with your usage and the tariff. SP Group publishes the household electricity tariff and revises it every quarter, so check the current rate there. To estimate an appliance's running cost, use the electricity cost calculator.
Power rating and how you use hot water
Instant heater power consumption appears on the Energy Label as the rated input power in kW. A higher kW instant heater draws more power while it is running. But, as the NEA guide notes, an instantaneous heater only uses energy while water flows through it. The energy it uses depends on both that rating and how long hot water is actually running.
According to NEA, a storage heater left switched on keeps using energy to heat water, whether or not anyone needs hot water. The hours it stays on count, as well as how much hot water you draw.
Usage matters for either type. Think about:
- how many people shower each day, and for how long
- whether anyone uses a bathtub
- whether two bathrooms need hot water at the same time
- how many hours a storage heater stays switched on
Heat pump and gas options
NEA's Resource Efficiency Guide says an electric heat pump water heater is more energy efficient than an electric instantaneous or storage water heater. The same guide suggests designing hot water pipes so hot water reaches the taps quickly, which is worth raising with your plumber if you are renovating.
The Energy Label also covers gas instantaneous water heaters, as well as heat pump models. If either is on your shortlist, read its label in the same way: check the type, the ticks and the annual energy cost.
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Compare plumbersWhich one should you choose?
Start from NEA's efficiency advice, then match it to your home:
- One bathroom, showers only. An instant heater fits NEA's advice, since it only uses energy while water flows.
- Several bathrooms or a bathtub. Ask a plumber whether one heater can serve them at once. If you choose storage, NEA says to pick a capacity that meets your needs.
- Limited space. Ask the plumber where each type of unit would go in your flat.
- Efficiency first. NEA says an electric heat pump water heater is more efficient than electric instant or storage heaters.
NEA's buying tips suggest looking at life cycle cost, not just purchase price. Life cycle cost is purchase price + annual energy cost x lifespan in years. Take the annual energy cost from each model's Energy Label. A model that costs more to buy can still have a lower life cycle cost if it uses less energy.
The price of the unit and fitting depends on the model and the job. Read the water heater replacement cost guide before you ask for quotes.
If an instant unit suits your home, you can browse companies that install instant water heaters.
Questions
Does a storage water heater use electricity all the time?
Only while it is switched on, including when nobody needs hot water. NEA says storage water heaters continue to use energy to heat water when they are left switched on. An instantaneous heater only uses energy to heat water while water flows through it.
Should I switch off my storage water heater after use?
NEA says a storage water heater keeps using energy to heat water while it is left switched on. Switching it off when you do not need hot water avoids that standby reheating. Allow time for the water to heat again before you need it.
Where can I see how much a water heater costs to run?
Check the Energy Label. NEA's label shows each model's annual energy cost and consumption, based on assumptions of 27 cents per kWh and 3 showers a day. Your actual cost depends on your usage and the current tariff, which SP Group publishes.
Is a heat pump water heater more efficient?
Yes, according to NEA. Its guide says an electric heat pump water heater is more energy efficient than an electric instantaneous or storage water heater. Heat pump models also carry the Energy Label, so you can compare their annual energy cost.
Does a higher kW instant heater cost more to run?
It draws more power while it is running, but an instant heater only uses energy while water flows. Its running cost depends on that power rating and on how long you use hot water. Compare the annual energy cost on each model's Energy Label, not the kW figure alone.
Which water heater suits a flat with two bathrooms?
It depends on your household. Consider whether both bathrooms need hot water at the same time and whether anyone uses a bathtub. NEA favours instantaneous heaters for efficiency and says to choose a suitable capacity if you prefer storage. Ask a plumber to size the setup, and compare plumbers first.
Practical guidance for planning a home job in Singapore. Company prices come from the HomezyPro directory, each linked to its source; rules and safety points link to the agency or manufacturer that sets them. This is not a site inspection, a quote or professional advice for your home.
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