What is the best instant water heater in Singapore?

Search for the hottest instant heater and you will find brands, not numbers. The number is simple. An instant heater adds a fixed amount of heat per second, so the more water you push through it, the less each litre warms up. Every model in our table below lists 3.3 kW or 3.5 kW where the rating is stated.

Here is how much a heater can raise the water temperature at each flow, before any heat loss. Rheem rates its tank heaters with water coming in at 25°C, so the last two columns use the same starting point.

Two things follow. The gap between a 3.3 kW and a 3.5 kW heater is about 1°C at normal flow. And turning the flow down by one litre a minute changes the temperature more than any brand switch will. Toshiba caps the DSK33ES5SB at 48°C at the outlet, which is the only maximum temperature we found published by a maker.

We checked each model on a brand page or a Singapore retailer's own listing. Prices are the listed price on the day we checked, often a promotion, and they change. Where a spec was not stated anywhere we looked, the table says so.

The Rubine RWH-3388 is also sold as the black RWH-3388BHP at S$400 on Casa's shop. Fujioh's FZ-WH5133 range carries a 5-year element warranty too, but we could not find a Singapore price for it, so it is not in the table.

The Mistral MSH99 is the one we would check most before paying. Its manual shows a rain shower, a DC pump and an ELCB, and at S$359 it is priced with the Ariston, but the Harvey Norman listing gives no warranty period. Ask the seller in writing.

One request we could not fill is a compact heater for a basin or kitchen tap. All eight models are shower units. For a basin, shops sell small under-sink storage tanks instead, such as Rubine's 15-litre Matrix under-sink unit at S$460 on Casa's shop.

A DC pump is worth paying for when water barely trickles out on the top floors of a block or in a landed home's upstairs bathroom. It raises the flow so the heater switches on reliably and the spray feels like a shower.

It does not add heat. Go back to the first table: if the pump lifts your flow from 3 to 5 litres a minute, the outlet temperature drops by about 6°C on the same 3.3 kW element. On a floor where the flow is already fine, a pump model mostly gives you a stronger, cooler shower.

Rain showers have the same limit. A wide head needs more water to feel full, and an instant heater spreads the same 3.3 kW over all of it. If two or more people want a hot rain shower, look at a tank instead: see instant vs storage.

• SAFETY Mark. Water heaters are Controlled Goods in Singapore and must carry it to be sold here. Casa's listing for the RWH-933P prints its Safety Mark number (211065-11). Avoid overseas listings that do not show one.
• Earth-leakage protection. Three of the eight state a built-in cut-off, on the listing or in the manual: Champs Virgo Ultra (double-pole RCD), Mistral MSH99 (ELCB, trips at 15 mA) and Ariston Aures Premium+ (ELCB). The other five may have protection, but the Singapore listings we read do not say so. Ask.
• WELS ticks. PUB's water efficiency labels cover taps, mixers, cisterns, flush valves, washing machines and dishwashers. Water heaters are not on the list, and showerheads are only voluntary, so a heater with no ticks is not breaking any rule.
• Splash rating. The Ariston Aures Easy, Champs Auriga Core and Toshiba list IP25. That is normal for a unit mounted beside a shower.

We wanted to rank these on maximum outlet temperature at a fixed flow. Only Toshiba publishes a maximum (48°C), and no maker gives it at a stated flow, so that ranking is not possible from public data. Two of the eight do not even give a kW figure on the Singapore listings we read: the Champs Virgo Ultra and the Ariston Aures Premium+. The Ariston's model code ends in 3.3, which suggests 3.3 kW, but the page does not say so.

Warranty wording varies too. Rubine and Fujioh split it into 5 years on the heating element and 1 year on everything else. Champs lists 24 months with no split. A long element warranty does not cover the pump, the control board or the shower set, which are the parts more likely to need a call-out.

An instant heater does not need a PUB Licensed Plumber. PUB treats it as simple plumbing work, and that includes the pipe from the stop valve to the heater. The electrical side is different: a new power point or a circuit upgrade must be done by a Licensed Electrical Worker (LEW).

A straight swap on the same wall, reusing the same point, sits at the low end. Moving the heater, drilling hard tiles for a rain shower rail, or a point that cannot take a 3.3 kW load pushes it up.

We install and replace instant heaters island-wide, 24/7. Send a photo of the old unit's label and the wall it sits on through WhatsApp, and the price is agreed before work starts. Workmanship carries a warranty of 1 week to 1 month depending on the job, and the heater keeps its manufacturer's warranty. See instant water heater installation.

An instant heater serves one shower point. If the kitchen sink, a second bathroom or a bathtub needs hot water, you need one heater per point or a tank. Two people showering back to back is fine; two at the same time needs two heaters.

If you are leaning towards a tank, our storage heater comparison covers sizes and models, and the water heater brand overview covers brands across both types. For a tank in a flat, read the HDB storage heater notes first, because a tank needs a PUB Licensed Plumber and an instant heater does not. All types and price bands are on the water heaters page.