Is a heat pump water heater worth it in the UK

It is usually worth it where hot water is currently heated by an immersion element and there is a room with enough air, such as a utility room or garage. Where a healthy gas boiler already heats a good cylinder, the saving is small and rarely pays back the higher purchase cost.

Can a heat pump water heater go in an airing cupboard

Rarely without ducting. The unit needs a minimum volume of air to draw heat from, and an ordinary airing cupboard is too small. With ducting to bring air in and take cooled air out, some models can be fitted in smaller spaces. Check the maker's minimum room size first.

Do heat pump water heaters work in winter

Yes, because most are indoors and draw on room air, which stays warmer than outside air. In an unheated garage or outbuilding the efficiency drops in cold weather and the backup immersion element does more of the work.

Does a heat pump water heater need a G3 qualified installer

If it is an unvented unit, which most are, yes. It falls under Part G3 like any unvented cylinder, needs notifying when installed, and its safety valves should be checked every year by someone qualified for unvented work.

Is a heat pump water heater the same as a heat pump cylinder

No. A heat pump water heater has its own small heat pump built in and heats only your hot water. A heat pump cylinder is a cylinder with a large coil, designed to be heated by a separate outdoor air source heat pump that also runs the central heating.

Can I get a grant for a heat pump water heater

The Boiler Upgrade Scheme is aimed at heat pumps that provide both heating and hot water, and as its rules have stood a hot water only unit does not qualify. Scheme terms change, so check the current rules on the government website.

Heat Pump Water Heater: Is It Worth It in a UK Home?

A heat pump water heater is worth it mainly in homes that heat their water with electricity today, through an immersion heater or an electric cylinder, and that have a room where the unit can breathe: a utility room, a garage or a large cupboard with ducting. In that situation it produces the same hot water for a fraction of the electricity an immersion element uses. In a home with a working gas boiler and a good cylinder, the saving is much smaller and rarely pays back the cost of the unit. This guide explains what these all in one units are, how they differ from the cylinder that goes with a full heat pump system, and the questions that decide whether one suits your property.

What a heat pump water heater is

A heat pump water heater is a hot water cylinder with a small air source heat pump built into the top. The heat pump draws air across a cold coil, extracts heat from it, raises that heat to a useful temperature and passes it into the stored water. You will also see it called a hot water heat pump, an air source heat pump water heater or an all in one heat pump cylinder. Ariston's Nuos range is one of the better known examples in the UK, and several cylinder makers sell their own.

Most units also have an ordinary immersion element as a backup, for very cold spells, for a fast boost when the household needs a lot of water at once, and for the periodic higher temperature cycle used to keep the stored water safe.

It is not the same thing as the cylinder you get with a whole house air source heat pump. That system has a large outdoor unit heating the radiators and a separate cylinder with an oversized coil. We cover that setup in our guide to the heat pump cylinder. An all in one water heater heats only your hot water, and the heat pump sits indoors on the cylinder itself.

Why it uses less electricity than an immersion heater

An immersion element turns each unit of electricity into one unit of heat. A heat pump uses electricity to move heat that is already in the air, so it delivers several units of heat for each unit it consumes. How many depends on the temperature of the air it draws in and how hot it has to make the water: warm air and a moderate target give the best results, a cold garage in January gives the worst.

That is why the saving is largest for homes currently paying for immersion heated water at a standard rate. If that describes you, our guide to immersion heater running cost shows what the element is costing now, which is the figure a heat pump water heater would be reducing.

Against a gas boiler the picture is different. Gas usually costs less per unit of heat than electricity, so a heat pump water heater saves far less, and in some homes nothing at all, compared with a well controlled boiler heating a well insulated cylinder.

The room matters more than the unit

A heat pump water heater takes heat out of the room it stands in, so the room gets cooler and drier while it runs. In a warm utility room with a tumble dryer, that is a bonus. In a small airing cupboard it simply will not work, because the unit soon cools the air it relies on.

Space and air volume. Each maker states the minimum room size, or requires ducting to bring air in and send the cooled air out. A standard airing cupboard is almost always too small without ducting.
Height and weight. The heat pump sits on top of the cylinder, so these units are taller than a conventional cylinder of the same capacity, and heavy when full.
Noise. There is a fan and a compressor, similar to a dehumidifier. Next to a bedroom it may be noticed at night.
Condensate. Cooling the air produces water, which needs a drain.
Cold spaces. In an unheated garage in winter the unit works harder and leans more on its backup element, which cuts the saving.

Unvented rules, safety and servicing

Most heat pump water heaters sold in the UK are unvented, so they run at mains pressure and fall under Part G3 of the Building Regulations like any other unvented cylinder. That means an installer qualified for unvented work, notification of the installation, and the usual safety kit: expansion vessel, pressure reducing valve, temperature and pressure relief valve and a tundish with a properly run discharge pipe. The annual check of those safety devices is the same job as on any unvented cylinder.

Heat pumps are at their most efficient heating water to a moderate temperature. Stored water should still be held hot enough to control Legionella, which is why these units run a regular higher temperature cycle, often using the backup element. Our guide to Legionella hot water temperature explains the figures that matter.

The refrigerant side of the unit is sealed. Faults inside it are a job for the maker's approved engineers, while the water side, valves, leaks, the element and the pipework, is ordinary cylinder work.

Are there grants for a heat pump water heater?

The government Boiler Upgrade Scheme in England and Wales is aimed at heat pumps that replace a fossil fuel boiler and provide both heating and hot water. As the scheme rules have stood, a heat pump that heats hot water only does not qualify. The terms do change, so check the current rules on the government website before you rely on it either way, and be wary of anyone promising a grant for a water only unit without showing you the scheme terms.

Heat pump water heater vs the alternatives

The honest comparison depends on what heats your water now and what you are trying to fix: the running cost, the space, or a system that has failed.

Against an electric cylinder with immersion elements on an off peak tariff: the heat pump uses much less electricity for the same water, but costs more to buy and needs a suitable room. Our guide to the electric hot water cylinder covers the simpler option.
Against a solar diverter on an existing immersion: if you have solar panels, a diverter uses your surplus for free and costs little to fit, though it only helps when the sun is out.
Against a heat battery: a heat battery saves space rather than energy, and suits small flats where a tall cylinder cannot go. We compare those in our heat battery vs hot water cylinder guide.
Against a gas boiler and cylinder: if the boiler is healthy, keeping it usually makes more financial sense for now.
Against an instant electric heater: only sensible for a single outlet, as explained in our guide to choosing an instant water heater or hot water cylinder.

Who a heat pump water heater suits

It suits an all electric house with a utility room, garage or basement where the unit has the air it needs, a household that currently relies on an immersion heater for all its hot water, and homes with solar panels that want to make more use of daytime generation. It also suits people planning to remove a gas boiler later who want the hot water side sorted first.

It does not suit a flat whose only option is a small airing cupboard, a home with a healthy gas boiler and nothing to gain, or anyone who needs a very fast recovery for several showers back to back, unless the cylinder is sized generously and the backup element is accepted as part of the running cost.

Getting the right advice

We fit, service and repair unvented cylinders, and the water side of a heat pump water heater is the same work. We will tell you if a straightforward replacement or an off peak electric cylinder would serve you better. If your cylinder has failed and you are weighing up options, our hot water cylinder replacement service covers the whole job, and our unvented cylinder installation work always starts with a mains pressure and flow test.

Call 020 4652 5111 to talk it through or book a survey. Our rates are on the pricing page and are agreed before we attend.

Questions we get asked

Is a heat pump water heater worth it in the UK: It is usually worth it where hot water is currently heated by an immersion element and there is a room with enough air, such as a utility room or garage. Where a healthy gas boiler already heats a good cylinder, the saving is small and rarely pays back the higher purchase cost.
Can a heat pump water heater go in an airing cupboard: Rarely without ducting. The unit needs a minimum volume of air to draw heat from, and an ordinary airing cupboard is too small. With ducting to bring air in and take cooled air out, some models can be fitted in smaller spaces. Check the maker's minimum room size first.
Do heat pump water heaters work in winter: Yes, because most are indoors and draw on room air, which stays warmer than outside air. In an unheated garage or outbuilding the efficiency drops in cold weather and the backup immersion element does more of the work.
Does a heat pump water heater need a G3 qualified installer: If it is an unvented unit, which most are, yes. It falls under Part G3 like any unvented cylinder, needs notifying when installed, and its safety valves should be checked every year by someone qualified for unvented work.
Is a heat pump water heater the same as a heat pump cylinder: No. A heat pump water heater has its own small heat pump built in and heats only your hot water. A heat pump cylinder is a cylinder with a large coil, designed to be heated by a separate outdoor air source heat pump that also runs the central heating.
Can I get a grant for a heat pump water heater: The Boiler Upgrade Scheme is aimed at heat pumps that provide both heating and hot water, and as its rules have stood a hot water only unit does not qualify. Scheme terms change, so check the current rules on the government website.