Guides · Hot water
Point-of-use electric water heaters
Small undersink and oversink electric water heaters explained: how they differ from a boiling-water tap or a cylinder immersion, vented and unvented types, where they make sense, and why the electrics need a qualified electrician.
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A point-of-use water heater is a small electric heater that sits right next to the tap it serves, usually in the cupboard under a sink or on the wall above it. It heats water for that one tap, or sometimes two close together, instead of drawing hot water along a long pipe from a boiler or cylinder.
This page is about electric heaters only. It does not cover gas water heaters of any kind. If you have a gas appliance that heats water, any work on it is for a Gas Safe registered engineer, and when to call a Gas Safe engineer explains why.
How it differs from other hot water
A boiling-water tap heats water close to boiling for drinks and cooking, from a tank under the sink, and delivers it through a special tap. A point-of-use heater delivers ordinary hot water for washing. Boiling water taps covers the other kind.
A cylinder immersion heats a large store of water in an airing cupboard for the whole house. A point-of-use heater is far smaller and serves a single spot. Hot water cylinders and immersions explains the whole-house version.
An instantaneous electric heater heats water only as it flows, with no store. These usually need a much larger electrical supply than a small storage heater. Some people use the term point-of-use for both; this page is mainly about the small storage kind.
Where they make sense
- A cloakroom basin, utility sink or garage sink a long way from the boiler, where hot water takes a long time to arrive.
- An outbuilding or office with a cold supply but no hot.
- A kitchen or basin in a home where the main hot water comes from a cylinder that is not always heated.
- Reducing the amount of cold water run off before the hot arrives at a distant tap.
They are not a replacement for a whole-house hot water system. A small store runs out quickly if you fill a bowl or a bath, then needs time to reheat.
Vented and unvented types
Small storage heaters come in two broad types.
Vented, or open-outlet, heaters are not under mains pressure. They usually need a particular kind of tap, supplied or specified by the maker, that controls the cold water going in rather than the hot coming out. As the water heats and expands, it drips from the spout. That is normal for this type.
Unvented heaters work at mains pressure and can feed an ordinary tap. They need safety devices to deal with expansion and pressure, often sold as a kit. Unvented hot water is controlled under the Building Regulations in England; the GOV.UK Approved Document G page covers hot water safety. Makers set out who may fit their units. Unvented cylinder basics explains the principle on the larger scale. Ask your installer which rules apply to the heater you choose and whether it needs to be notified.
Electrics: a job for a qualified electrician
Every point-of-use heater needs a suitable electrical supply. Some plug in; others must be permanently connected, and larger ones may need their own circuit. Which is right depends on the heater and on your existing wiring. That is a job for a qualified electrician. Work on electrics in homes in England is covered by Part P of the Building Regulations; the GOV.UK Approved Document P page is a starting point.
We do not give wiring instructions. Water and electricity are close together in a sink cupboard, so the heater's position, the maker's clearances and protection from drips all matter. Do not remove the heater's cover.
The plumbing side
The heater connects into the cold supply, and its hot outlet goes to the tap. An isolation valve on the cold feed lets the unit be serviced. Unvented units need their safety devices and a discharge route as the maker specifies. Leave room to reach the valves and to read the label. Kitchen sink installs covers how a cupboard is usually laid out, and flexible tap connectors covers the hoses commonly used.
If you already have an under-sink water filter or a boiling-water tap tank, space can be tight. Measure the cupboard before buying, including the depth with the door shut.
Scale and maintenance
Like a kettle, a small heater collects scale in hard water areas, which can slow heating and shorten its life. Some have a replaceable anode or element. The maker's manual will say what can be serviced. Limescale explains how hardness affects appliances.
One undersink heater Wickes lists
We haven't tested this. Figures are as the maker states them (checked 13 November 2026).
Ariston Andris Lux undersink electric water heater, 6L. Wickes lists it as an electric undersink storage heater storing up to 6 litres, with a manual dial for temperature and a maximum operating temperature of 60°C. It says unvented installation kits are available separately. Those are the seller's words. Check whether the version you buy is set up for a vented tap or an unvented kit, and ask your installer about the electrical supply.
Why does my undersink heater drip from the tap?
On a vented, open-outlet heater, water expands as it heats and drips from the spout. That is normal. On an unvented heater, a drip or discharge is not normal and needs an installer to check it.
Can I fit a point-of-use water heater myself?
The electrical supply is a job for a qualified electrician. Unvented units have their own safety rules and the maker will say who may fit them. Check before buying.
Is a point-of-use heater cheaper to run?
It can waste less heat than running hot water along a long pipe, but that depends on how you use it and your tariff. There is no single answer.