Point of Use Water Heaters: Are They Worth It?

Updated July 2026 · Emergency Plumber Chelsea

The two main types. Stored under-sink heaters hold a small amount of water, typically a few litres up to around 15, and keep it hot, ready at the tap. Instantaneous heaters store nothing and heat the water as it flows through, like a small electric shower. Stored units are the usual choice for a kitchen or cloakroom basin. Instant units are compact and never run out, but their flow of hot water is limited by how much power they draw.

Why instant units give a limited flow. Heating water takes a lot of power. A small instant unit that plugs into an ordinary socket at around 3 kW can only raise about one to one and a half litres a minute from cold mains temperature to comfortably warm, which is fine for washing hands at a basin but frustrating for filling a kitchen sink. Larger instant units give a proper flow but draw much more current and need their own dedicated circuit from the consumer unit, installed by a qualified electrician. If an instant heater is on your list, check the supply first, because the electrics can decide the choice for you.

Where a point of use heater makes sense. The classic case is a cloakroom or kitchen at the far end of a long pipe run from the boiler or cylinder. Every time you open the tap you draw off all the cold water sitting in that pipe before hot arrives, which wastes water and time. A heater at the tap solves both. Other good uses are a new utility sink or basin in a basement or loft conversion where running hot pipework back to the cylinder would mean lifting floors, a garden room, studio or mews office with a cold supply only, and a backup at one kitchen tap for a household that is on an old system prone to breakdowns.

Where it does not make sense. A point of use heater will not run a bath or a shower, and electric showers, which heat water on demand at much higher power, are a separate product covered by our shower repairs service. It is not a practical way to give a whole flat hot water, and in most homes a properly sized boiler or cylinder is cheaper to run than electric heating at several taps. If hot water is slow to arrive everywhere, not just at one tap, the problem is more likely the main system; our guide to hot water not hot enough covers the common causes.

Running costs. Point of use heaters are electric, so each litre they heat costs more than water heated by a gas boiler. Against that, a stored unit only heats a few litres and an instant one only heats what you use, and you stop wasting the cold water and heat lost along a long pipe run. For a single rarely used basin they are cheap to run. For a busy kitchen tap used all day, a stored unit on a timer, or improving the pipework from the main system, may work out better. Our article on immersion heater running costs explains how to estimate the cost of heating water electrically.

Vented or unvented under-sink units. Some stored heaters are open-outlet, or vented, types that must be used with a special tap supplied by the manufacturer, because the heater itself is never under mains pressure. Others are unvented and can feed an ordinary mixer tap at mains pressure. Unvented units have to be fitted with the manufacturer's safety valves and a proper discharge arrangement. Small units of 15 litres or less fall outside the stricter Building Regulations rules that apply to larger unvented cylinders, but they still need to be installed correctly. For the bigger version of the same choice, see vented vs unvented hot water cylinders.

What sets the installation cost. The heater is only part of it. The main factors are the type and size of unit, whether there is room for it in the cupboard under the sink, whether a suitable electrical supply is already there or a new circuit is needed, how the cold feed and hot outlet connect to the existing tap, and for unvented units, the safety valve and discharge pipe. Fitting a stored heater under an existing kitchen sink with a spur already in place is a modest job. Adding a new basin, new pipework and a new circuit in a garden room is a bigger one. We give a clear price once we have seen the space.

Hygiene and temperature. A stored heater should keep its water hot enough to limit the growth of bacteria, and most have a thermostat that is set at the factory for that reason. At a basin used by children or older people, a thermostatic mixing valve can blend the outlet down to a safer temperature; our guide to thermostatic mixing valves explains how they work. If a unit sits unused for a long time, for example in a holiday let or a rarely used guest cloakroom, run the tap through before using it.

Point of use heater or a boiling water tap? They do different jobs. A point of use heater gives normal hot water for washing. A boiling water tap gives near-boiling water for drinks and cooking and is not meant for washing up. Some people fit both. If boiling water is what you are after, read our guide on whether a boiling water tap is worth it.

Getting one fitted in Chelsea. Emergency Plumber Chelsea looks at where the hot water is coming from now, how far it travels, the space under the sink and the electrical supply, and tells you honestly whether a point of use heater is the right fix or whether the main system needs attention. You get a clear price before work starts, and there is no call-out fee on jobs over 3 hours. See our plumbing installation service or call 020 3002 6667 for SW3, SW10, Knightsbridge, Sloane Square, South Kensington and Fulham.

Quick tips

• Time how long hot water takes to arrive at the tap; a long wait at one outlet only is the classic case for a point of use heater.
• Check the electrical supply before choosing an instant unit; bigger models need their own circuit.
• Measure the cupboard under the sink before choosing a stored unit, allowing room for the waste trap.
• Open-outlet heaters need the matching tap from the manufacturer; an ordinary mixer will not do.
• If hot water is slow at every tap, look at the main system before adding heaters.

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