Water heater size calculator

How to use this water heater size calculator

Pick the heater type, then enter the hot water outlets this heater supplies at the same time. Working as a storage heater litres calculator, it matches your combination to a row in Joven's sizing table and shows that capacity and row.

Inputs: what runs at the same time

The tool asks about outlets in use together because Joven's table lists each capacity against the showers, sinks and baths running at once. It gives no litres per person, so household size is not an input.

• Heater type: storage or instant. Instant shows a note that this table does not size instant heaters.
• Normal showers: 0 to 3.
• Rain showers: by size, 6, 8, 10 or 12 inches (15cm, 20cm, 25cm or 30cm).
• Sinks: 0 or 1.
• Long bath: yes or no.

Count only the outlets on this heater that often run together.

Result: instant or storage, and litres

For a storage heater, you get the smallest capacity in Joven's table whose listed use covers your combination (25, 35 or 38, 50 or 56, 68, or 91 litres), with the matching row. Combinations not in the table show "Outside Joven's table: ask the supplier."

The result also carries a reminder from NEA's guide for new home owners: an instantaneous heater is more energy efficient, and if you prefer storage, choose a capacity that meets your needs. NEA's energy saving tips add that switching a storage heater on 10 to 30 minutes before showering is enough. Compare instant water heaters and the instant vs storage running cost.

The calculator reads this table from Joven's help article:

How the calculation works (method and sources)

The calculator returns the smallest capacity whose row in Joven's table covers your combination. A row covers it if your outlets match one of its listed uses or are part of one, with fewer outlets of the same kinds and sizes. So a 6-inch rain shower alone gets 35 or 38 litres, the smaller of the rows that cover it.

Rain shower sizes are matched exactly: a 10-inch rain shower matches the 68 litre row and is never rounded to 8 or 12 inches.

The tool never extrapolates beyond Joven's table. For example, 3 normal showers and 1 sink appear in no row, so that combination gets "Outside Joven's table: ask the supplier." The energy reminder is NEA's advice and is not part of the sizing.

Limits of this calculator

The sizing comes from one manufacturer, so keep these limits in mind:

• Joven's table is guidance for its own storage heaters; other brands may differ.
• It does not size instant heaters and gives no litres per person.
• Water pressure, pipe runs and how long showers last are not modelled.

On pipe runs, NEA's guide suggests designing hot water pipes so hot water reaches the taps quickly. Ask companies offering water heater services where the heater will sit.

Before you buy or replace a heater

The Consumer Product Safety Office (CPSO) says electric storage and instantaneous water heaters are Controlled Goods and must carry the SAFETY Mark before they can be sold in Singapore. CPSO also says to hire a Licensed Electrical Worker (LEW) to wire the heater directly to the mains through a double pole switch, not to a 3-pin socket outlet, with no extension cords or multi-way outlets.

The Energy Market Authority (EMA) says wiring work at home should be carried out or supervised by an LEW, and to check the worker's licence card before any electrical work starts. EMA says electrical work in an HDB flat needs a Licensed Electrician, the class of LEW approved for loads of up to 45kVA.

On the water side, PUB's simple plumbing works list, which handymen may do, includes replacing or removing any pipe between a stop valve and an instantaneous water heater. Pipework for a storage water heater is not on that list, so it needs a PUB Licensed Plumber. Since 2018 it has been an offence to engage a plumber not licensed by PUB for regulated works. Our guide to water heater installation steps covers the job itself.

When you compare models, NEA's Energy Label on a water heater shows its type, its rated input power or nominal heat input in kilowatts (kW) and, for a storage heater, its capacity in litres, so you can match it to your result.

What you pay depends on the heater and the job. See water heater replacement cost, plumbing costs and, if you are open on fuel, gas or electric water heater.

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