Point of use water heater buying guide
Updated: 17.10.2026
You have a cold tap in a cloakroom, a garden room or a kitchenette, and the boxes on amazon.co.uk do not share one job. A point of use water heater buying guide names the outlet before the kilowatt figure, because a basin, a bowl and a shower need different litres and circuits. Listings from 15 October 2026 are on the [point-of-use water heater comparison](/hub/hot-water/point-of-use-water-heater). We used those listings and public UK sources, not a lab. A qualifying purchase can earn a commission at no extra cost to you.
You have a cold tap in a cloakroom, a garden room or a kitchenette, and the boxes on amazon.co.uk do not share one job.
You have a cold tap in a cloakroom, a garden room or a kitchenette, and the boxes on amazon.co.uk do not share one job. A point of use water heater buying guide names the outlet before the kilowatt figure, because a basin, a bowl and a shower need different litres and circuits. Listings from 15 October 2026 are on the point-of-use water heater comparison. We used those listings and public UK sources, not a lab. A qualifying purchase can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Type | Power | Stored water | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  COMFEE' COMFEE' 10 L undersink | Undersink store | 2 kW | 10 litres | 9.6 | about £79.99 | View offer |
| Preis-Tipp |  Triton Showers Triton T30i handwash | Instant handwash | 3 kW | None | 9.0 | about £55.99 | View offer |
| Alternative |  Ariston Ariston Andris R 15 L undersink | Undersink store | 3 kW | 15 litres | 9.0 | about £133.19 | View offer |
On this page
Start with the outlet
The outlet decides the heater. A cloakroom basin is a short draw. Heathfield’s retail rule of thumb, a planning aid rather than a measured test, puts a hand basin at about 3.5–5.7 kW on demand, or about 5 litres stored. The Triton T30i is the 3 kW handwash in this set, at about £55.99, and its 842 reviews describe cloakrooms, workshops and sheds.
A kitchen sink is a bowl: about 10–15 litres stored, or 6–12 kW if the heat is instant. The COMFEE' at about £79.99 and the Ariston Andris R at about £133.19 sit in that band. At 2 litres a minute, 3 kW adds about 21°C; at 8 litres a minute about 5°C. That calculation, not a test, is why a cheap 3 kW listing is not a sink heater. A 3 kW shower head is not a shower, and a bath is outside this category. The room is on the hand basin or kitchen sink page.
Stored litres or an element
Storage gives a proper flow until the tank is empty, then a wait. Instant heat does not run out, but the rise is capped by the element and by how far you open the tap. For one washing-up bowl, the rule of thumb is about 10 litres stored. Ariston’s UK page for the 15 litre undersink 3 kW model quotes about 18 minutes to heat, energy class B and load profile XXS.
A retail rule of thumb is about 12 minutes for 5 litres and about 25 minutes for 10 litres from cold. Use that as a gap between bowls, not as a ranking. The FVSTR title says a UK plug, 2 kW and 2.5 gallons. The specification says 120 V and 1,500 W. Treat that clash as a buying check, not a settled 230 V heater. The storage-or-instant choice is on the undersink or instant page.
The tap and the 15 litre line
An open-outlet store must use the maker’s vented tap, because that outlet is the vent. The spout drips as the water expands, and capping the drip is how people burst a small cylinder. Hyco’s undersink instructions and Heatrae Sadia’s notes treat the drip as normal and warn against over-tightening. Many instantaneous heaters do not need that tap. Filling, and what to do with the drip, is on the install guide.
An unvented store needs the maker’s safety kit and a discharge you can see. In England, Approved Document G says a store of 15 litres or less, with suitable safety devices, generally meets G3(3). Notification often falls away only when the electrics are also non-notifiable. The safety duty remains. England and Wales still want a servicing valve, and an unvented store above 15 litres needs temperature relief. Scotland and Northern Ireland use their own rules. HSE HSG274 asks for 50–60°C on a store of 15 litres or less, or a very high turnover. Mix down at the tap.
Power, plugs and the energy label
At 230 V, 3 kW is about 13 A, 6 kW about 26 A, and 12 kW about 52 A. Those are currents from the wattage, not a cable design. A 6 kW or 10–12 kW heater is not a 13 A plug. The Stiebel Eltron DCE-X 10/12, at about £412.86, is the high-power instant listing here, and reviewers describe a dedicated cable rather than a socket. The IET, in Wiring Matters for September 2025, says a long 3 kW immersion is a poor match for a BS 1363 plug. A handwash that only heats while water flows is a shorter duty, so a blanket ban on every 3 kW plug would overclaim. A new circuit is notifiable in England under Part P.
Energy class A on the COMFEE' and class B on the Andris R follow the load profile in retained regulation 812/2013. The letter is not a monthly bill. Price comes last, after the outlet, the litres or kilowatts, the tap and the amps.
Common questions
How many litres do I need for a cloakroom basin?
A cloakroom basin is a short draw, not a bowl. Heathfield’s rule of thumb is about 5 litres stored, or an on-demand heater around 3.5–5.7 kW. In this set the Triton T30i is the 3 kW handwash aimed at that job. A 10 or 15 litre tank will also wash hands, though you then heat a store you may not need, and you still have to match the tap.
Is 10 litres enough to wash up?
Ten litres is the rule-of-thumb size for one washing-up bowl, if you accept a wait while the tank recovers. The COMFEE' 10 litre, 2 kW store is the listing in this set at that size. UK reviewers describe holiday-home and garden-room sinks. It is not a second bowl straight away, and it is not a shower store.
What kilowatts does a kitchen sink actually need?
On an instant heater, a kitchen sink wants something nearer 6–12 kW, not 3 kW. The calculation is about 21°C of rise at 2 litres a minute from 3 kW, and about 5°C at 8 litres a minute. If you would rather keep a modest circuit, store 10–15 litres instead. The Stiebel at 10/12 kW is the high-power instant listing here, and it needs its own circuit.
Do I need a special tap?
You need the maker’s open-outlet tap on a vented store, because that outlet is the vent and it is meant to drip while the water heats. An unvented store can feed a normal tap if the safety kit is fitted. Many instant heaters do not use a vented tap. Do not put a standard mixer on an open-outlet tank.
Is a heater under 15 litres outside Building Regulations?
No. In England, a store of 15 litres or less with suitable safety devices generally meets G3(3), and notification often falls away only if the electrics are also non-notifiable. The safety devices, the servicing valve and the discharge route still apply. A new circuit, or work in a bathroom zone, can be notifiable even when the tank is small.
Can I use a normal 13 A socket?
A 6 kW or 12 kW heater cannot. At 230 V those loads are about 26 A and about 52 A. A 3 kW handwash that only heats while water flows is a shorter duty than a long immersion, and the IET has warned that a long 3 kW immersion is a poor match for a BS 1363 plug. Treat a UK-plug claim next to 6,000 W as a contradiction.
Does energy class A mean a low bill?
No. The class letter depends on the load profile under retained regulation 812/2013. Class A on the COMFEE' and class B on the Andris R describe those declared profiles. They do not halve the cost of a tank that sits hot all day, and they say nothing useful about a 12 kW heater that only draws power when the tap is open.
Related pages
Sources
Public UK sources used for this comparison. Listing prices, stars, and review counts are from amazon.co.uk extracts dated 15 October 2026.
- Approved Document G, with 2024 amendments (retrieved 15 October 2026)
- Approved Document P, 2013 (retrieved 15 October 2026)
- Water Supply (Water Fittings) Regulations 1999 (retrieved 15 October 2026)
- HSE HSG274 Part 2 (retrieved 15 October 2026)
- IET Wiring Matters, September 2025 — 3 kW and BS 1363 (retrieved 15 October 2026)
- Retained regulation 812/2013, Annex II (retrieved 15 October 2026)
- Ariston Andris Lux, UK (retrieved 15 October 2026)
- Stiebel Eltron — instantaneous versus stored water heaters (retrieved 15 October 2026)