Most homes get their hot water from one place: a combi boiler or a cylinder heated by a boiler or heat pump. That works well until you need hot water somewhere the pipework doesn’t reach easily, such as a kitchen in a new extension, a utility room at the far end of the house, or a sink in a garden office. A point-of-use electric water heater fixes that by heating water right where it’s used.
This guide covers the two main types, what they cost to buy and run in the UK, the rules for fitting them, and when one is (and isn’t) the right answer. If you’re looking at hot water for the whole house, start with our guide to hot water cylinders instead. If you want near-boiling water for drinks, that’s a different product: see our guide to instant hot water taps.
The short version
- Two types: small storage heaters (usually 5 to 15 litres, under or over the sink) and instantaneous heaters that heat water as it flows.
- Storage heaters are the easy option: 1 to 3 kW, usually wired to a fused spur, and from around £140 for the unit.
- Instantaneous heaters never run out, but a kitchen sink model is typically 11 kW or more and needs its own circuit from the consumer unit.
- Running costs for a busy kitchen sink are roughly £100 to £140 a year at the October 2026 price cap.
- They are a fix for distance, not a cheaper way to heat water. If your main hot water comes from a heat pump, keep using it wherever the pipework allows.
When a point-of-use heater makes sense
The usual reason is distance. Every time you open a hot tap, the cold water sitting in the pipe has to run out before hot water arrives. A 10 metre run of 15 mm pipe holds about one and a half litres, so a sink a long way from the cylinder wastes water, wastes the heat left in the pipe afterwards, and keeps you waiting.
Common situations where a point-of-use heater is the sensible choice:
- A kitchen or utility room in an extension, a long way from the cylinder or boiler
- A sink in a garage, workshop or garden office with only a cold supply
- A cloakroom basin where running a hot pipe would mean lifting floors
- Hot water for washing up during the summer, when you’d rather not heat a whole cylinder (more relevant to oil and LPG homes than heat pump homes)
Where it usually isn’t the answer: replacing your main hot water. Heating water directly with electricity uses one unit of electricity for every unit of heat. A heat pump heating a cylinder typically delivers two to three units of heat for each unit of electricity, so if you have one, a point-of-use heater only earns its place where the pipe run is genuinely long. Our guide to how air source heat pumps work explains why.
Storage or instantaneous: the two types
Storage (small tank) heaters
These hold a small amount of water, usually 5 to 15 litres, and keep it hot with a 1 to 3 kW element, much like a mini cylinder. Under-sink models tuck into the cupboard; over-sink models hang on the wall above the tap. Because the element is small, most can run from a 13 amp fused spur rather than needing a new circuit.
There are two kinds, and the difference matters when you choose a tap:
- Vented (open outlet): the tank isn’t under mains pressure, so it needs a special vented tap or spout. You can’t use an ordinary mixer tap. They’re usually cheaper and simpler.
- Unvented: the tank runs at mains pressure through a pressure-reducing valve and expansion vessel, so it works with a normal mixer tap. More plumbing, more cost, better flow.
The catch with storage heaters is that they run out. A 10 litre tank is plenty for handwashing and a sink of washing up, but if you fill a bowl, rinse a few pans and then go back for more, you’ll be waiting for it to reheat.
Instantaneous (tankless) heaters
These heat water as it passes through, so they never run out and there’s no stored water losing heat between uses. The trade-off is power. Heating flowing water instantly needs a big element, and the flow rate you get depends on it.
- Small units (roughly 3.5 to 6.5 kW) suit a single handwash basin. Stiebel Eltron rates its smallest models at about 2 to 3 litres a minute.
- Larger single-phase units (roughly 7 to 14 kW) can supply a kitchen sink, at about 3.5 to 7 litres a minute depending on the model and how cold the incoming water is.
Even the larger units can feel slow when filling a washing-up bowl in winter, when the incoming mains water is coldest. Stiebel Eltron’s own guidance says a 12 kW single-phase heater can supply a kitchen sink where an endless supply matters more than fast flow, which is a fair summary.
Which type suits which job
| Storage (vented) | Storage (unvented) | Instantaneous | |
|---|---|---|---|
| Size or output | 5 to 15 litres | 5 to 15 litres | 3.5 to 14 kW single-phase |
| Electrical supply | Usually a 13 amp fused spur | Usually a 13 amp fused spur | Kitchen models need a dedicated circuit, often 50 amp or more |
| Tap | Special vented tap or spout | Normal mixer tap | Normal tap (some small units need a specific spout) |
| Runs out? | Yes, then reheats | Yes, then reheats | No, but flow is limited |
| Standing heat loss | Small, all day | Small, all day | None |
| Unit price | Around £400 for a 10 litre Heatrae Sadia Streamline | From around £140; up to around £880 for premium models | Around £310 to £430 for kitchen-sink sizes |
| Best for | Basins, cloakrooms, occasional use | Kitchen and utility sinks with a normal mixer | Sinks used often, where running out would annoy |
Prices are for the unit only, including VAT, and vary between merchants. Fitting is extra.
What they cost to buy and run
Buying. A basic 15 litre under-sink storage heater such as the Ariston Andris Lux can be had for around £140. A 10 litre Heatrae Sadia Streamline over-sink model is around £400, and premium unvented units such as the Heatrae Sadia Multipoint 10 list at up to around £880. Instantaneous heaters big enough for a kitchen sink, such as Stiebel Eltron’s DCE range, run from around £310 to £430.
Fitting. A storage heater going on to existing pipework with a fused spur nearby is usually a half-day job for a plumber, with an electrician for the spur if needed; expect roughly £150 to £350. An instantaneous kitchen heater costs more to fit, typically £350 to £700, because it needs a new cable from the consumer unit and sometimes a consumer unit upgrade. Get the electrician to check your supply before you buy.
Running. Heating 10 litres of water from about 10°C to 55°C takes roughly half a kilowatt-hour. A busy kitchen sink using around 20 litres of hot water a day therefore needs about 1 kWh a day for the water itself. Storage heaters add a little on top for heat lost from the tank, typically a few tenths of a kWh a day (check the product’s energy label).
At the October 2026 price cap average of about 26p per kWh, that works out at roughly £100 a year for an instantaneous heater and £130 to £140 for a storage heater at a busy kitchen sink. A cloakroom basin used for handwashing costs a fraction of that. If you’re on a time-of-use tariff, a storage heater with a timer can reheat on cheaper off-peak electricity; an instantaneous heater can’t, because it heats only when you open the tap.
Fitting one: the rules that apply
Unvented storage heaters (Building Regulations Part G3). Units holding 15 litres or less don’t need to be notified to building control and don’t need a G3 certificate, unless the electrical work is itself notifiable. They must still have the right safety controls, and the manufacturer will insist on a competent installer. Anything over 15 litres counts as an unvented hot water system and must be fitted by a G3-qualified installer and notified.
Electrical work (Part P). In England, adding a fused spur to an existing circuit outside a bathroom is not usually notifiable. A new circuit from the consumer unit, which most instantaneous kitchen heaters need, is notifiable, so use an electrician registered with a competent person scheme who can self-certify the work. The rules are slightly different in Wales; your electrician will know which apply.
Safe temperatures. Most units let you limit the outlet temperature. Around 50°C to 55°C is hot enough for washing up and reduces the risk of scalding, which matters with children or older people in the house. Storage heaters should still reach at least 60°C periodically to keep bacteria in check; the manufacturer’s instructions will say how.
Brands worth looking at
Amazon links are affiliate links: if you buy, I may earn a small commission at no extra cost to you. Check the model suits your electrical supply and tap before ordering, and see the fitting rules above.
- Heatrae Sadia: long-established UK brand. Streamline (vented, under or over sink) and Multipoint (unvented) cover most storage needs. Check on Amazon
- Ariston: the Andris range is the budget-friendly choice for small under-sink storage. Check on Amazon
- Stiebel Eltron: the specialist for instantaneous heaters, from small DEM basin units to the DCE range for kitchen sinks. Check on Amazon
- Redring: another UK name with a range of under-sink and over-sink storage heaters. Check on Amazon
Whichever brand you choose, check the warranty, whether parts such as elements and thermostats are easy to get, and that the unit physically fits the cupboard or wall space with room to service it.
Common problems and maintenance
- Water not hot enough: check the thermostat setting first. On a storage heater, the tank may simply have run out; on an instantaneous heater, try opening the tap less so the water spends longer passing the element.
- Slow flow: usually limescale in the tap aerator or the heater’s inlet filter. Cleaning both often fixes it.
- Noises: crackling or hissing from a storage heater usually means scale on the element. In hard water areas, descaling every year or two extends its life.
- Drips from an unvented unit: a small discharge from the relief valve while heating can mean the expansion vessel has lost its charge. Get it checked rather than ignoring it.
With basic care, most point-of-use heaters last around 8 to 12 years. Hard water shortens that, so a scale reducer on the supply is worth considering in hard water areas.
Frequently asked questions
Can I plug an under-sink water heater into a normal socket?
Some small storage units come with a plug, but most installers wire them to a fused spur so they can’t be unplugged by accident and the spur can be switched off for servicing. Instantaneous kitchen heaters can’t use a plug at all; they need their own circuit.
Do I need a G3-qualified installer for an under-sink heater?
Not for unvented units of 15 litres or less, which aren’t notifiable under Part G3. Over 15 litres, yes. Vented units aren’t covered by G3 at all. You should still use someone competent, as the manufacturer’s warranty will usually require it.
How much does a point-of-use water heater cost to run?
For a busy kitchen sink, roughly £100 to £140 a year at the October 2026 price cap. A cloakroom basin used only for handwashing costs much less.
Is an instantaneous or storage heater better for a kitchen?
A storage heater is cheaper and easier to fit, and suits light use. An instantaneous heater suits a sink used heavily, where running out would be a nuisance, but it needs a large dedicated circuit and gives a modest flow rate in winter.
Is it worth fitting one if I have a heat pump?
Only where a sink is a long way from the cylinder. A heat pump heats water more cheaply than direct electric heating, so for nearby taps it’s better to keep using the cylinder.
How long do they last?
Around 8 to 12 years with basic maintenance. Descaling in hard water areas makes the biggest difference.
Sources: electricity price from Ofgem’s price cap for October to December 2026; Part G3 notification from the government’s Part G FAQ; instantaneous heater outputs and flow rates from Stiebel Eltron UK; unit prices from UK merchants (Monster Plumb, Electrical Deals Direct, City Plumbing, Heatershop, Quality Heating), checked 7 October 2026.