Heat pump hot water: how it works and what to expect

This article was last reviewed on 1 July 2026. Energy rates are updated in line with Ofgem's quarterly price cap reviews.

If you're thinking about getting an air source heat pump, one of the first questions is usually about hot water. Can a heat pump heat your water as well as your home? The short answer is yes. Here's how it works and what to expect in a typical UK home.

How does a heat pump provide hot water?

An air source heat pump works by extracting heat from the outside air and using it to heat water. That water then circulates around your home through radiators or underfloor heating, and it also fills a hot water cylinder for your taps, showers and baths.

The key difference from a gas boiler is temperature. A boiler heats water to around 65 to 70°C. A heat pump typically heats water to 45 to 55°C, which is enough for space heating and hot water in most homes. Your installer will set the right flow temperature for your system during set-up.

Do you need a hot water cylinder with a heat pump?

Yes. Unlike a combi-boiler, which heats water on demand, a heat pump works best when it heats water gradually and stores it. A hot water cylinder is an essential part of a heat pump system.

Most heat pump installations use a dedicated heat pump cylinder, which is designed to work efficiently at the lower flow temperatures a heat pump produces. Standard cylinders designed for boilers can work but are less efficient. OVO's installation team will specify the right cylinder for your home as part of the system design.

Cylinder sizes vary depending on how many people live in the home. A typical three bedroom home with two to four people needs a cylinder of around 200 to 250 litres. Your OVO surveyor will confirm the right size for you.

How long does it take a heat pump to heat water?

Rather than heating water quickly on demand, the heat pump runs at a lower output for longer periods, keeping the cylinder topped up throughout the day.

In practice, most homeowners don't notice the difference. The cylinder stores enough hot water for typical household use and the heat pump keeps it at a continuous temperature. Running out of hot water is rare with a correctly sized system.

What temperature does a heat pump heat water to?

Heat pumps typically heat the cylinder to 50 to 55°C. This is warm enough for comfortable showers and baths and hot enough to prevent legionella bacteria from developing in the cylinder.

Most heat pump systems run an automatic legionella cycle once a week, briefly heating the cylinder to 60°C as a safety measure. This happens automatically and you don't need to do anything.

Can a heat pump provide enough hot water for a family?

Yes, for the vast majority of UK homes. A correctly sized heat pump and cylinder combination will comfortably meet the hot water demands of a typical family. The system runs continuously in the background, keeping the cylinder at temperature so hot water is always available.

Homes with unusually high hot water demand, such as multiple bathrooms in heavy use at the same time, may need a larger cylinder. Your OVO surveyor will ask about your habits as part of the free survey.

Does a heat pump work with an existing cylinder?

Sometimes. If your cylinder is a well insulated, unvented cylinder in good condition, it may be possible to keep it. However, many older cylinders are designed for the higher flow temperatures a boiler produces and don't work as efficiently with a heat pump.

OVO's installation team will assess your cylinder as part of the free survey and let you know whether it's compatible or whether a replacement is needed.

How much does it cost to run a heat pump for hot water?

Running costs for heat pump hot water depend on your cylinder size, how much hot water your household uses, and your electricity tariff. But the key figure to understand is the Coefficient of Performance (COP).

A heat pump typically achieves a COP of 2.5 to 3.5 for hot water heating. This means for every unit of electricity it uses, it produces 2.5 to 3.5 units of heat. A gas boiler operates at around 0.9. So a heat pump produces roughly three times as much heat from the same energy input.

Estimates based on a COP of 3.0 for hot water and typical cylinder reheat losses. Electricity at OVO's standard variable rate of 26.11p/kWh and gas at approximately 7.3p/kWh, both correct at 1 July 2026 following Ofgem's revised Typical Domestic Consumption Values and Q3 price cap. The gap between heat pump electricity costs and gas boiler costs has narrowed further as gas prices have risen more steeply than electricity in recent quarters, strengthening the running cost case for heat pumps. Actual costs vary by usage, tariff, and heat pump model.

Does a heat pump cylinder have an immersion heater backup?

Yes. Most heat pump cylinders include an electric immersion heater as a backup. This is there for two reasons: as a safety net if the heat pump needs servicing or is temporarily unavailable, and to run the weekly legionella safety cycle if needed.

The immersion heater uses more electricity than the heat pump itself, so it shouldn't be left on as the primary heat source. But knowing it's there provides peace of mind that you won't be without hot water if something needs attention.

OVO's heat pump installations always include a cylinder with immersion heater backup as standard.

What about solar panels and hot water?

If you have solar panels or are planning to install them alongside a heat pump, the two work well together. During the day, surplus electricity from your solar panels can be used to run the heat pump and top up the hot water cylinder, reducing how much electricity you draw from the grid. This is one of the reasons why solar and heat pump installations are increasingly common in the same home.

OVO installs both solar panels and heat pumps, so if you're considering both it's worth getting a combined survey to see how the two systems can work together for your home.

If you're thinking about switching from a gas boiler, you could get £7,500 off the cost of your heat pump through the Boiler Upgrade Scheme or £9,000 if you're currently on oil or LPG heating. OVO handles the application for you as part of the installation.

Can you schedule heat pump hot water to save money?

Yes, and this is one of the most effective ways to reduce running costs. Most modern heat pump controllers let you set a schedule for when the cylinder heats up. If you're on a time of use tariff with cheaper overnight electricity, you can set the heat pump to heat your water at night and store it for the day.

This works particularly well if you have solar panels. During the day, surplus solar electricity can be directed to run the heat pump and top up the cylinder, reducing grid imports further. OVO installs both solar panels and heat pumps, so if you're considering both it's worth asking about how the two systems can work together.

What about solar panels and hot water?

If you're thinking about switching from a gas boiler, you could get £7,500 off the cost of your heat pump through the Boiler Upgrade Scheme. If you're currently on oil or LPG heating, you can claim £9,000 — a temporary uplift available until 31 March 2027, so it's worth acting before that window closes. OVO handles the application for you as part of the installation.

OVO installs both solar panels and heat pumps, so if you're considering both it's worth getting a combined survey to see how the two systems can work together for your home.

FAQ

Do heat pumps provide hot water as well as heating?

Yes. An air source heat pump heats both your home and your hot water. The heated water is stored in a cylinder and drawn on as needed, in the same way as a standard hot water system.

Do I need a new cylinder when I get a heat pump?

In most cases, yes. Heat pumps work best with a cylinder designed for lower flow temperatures. Your OVO installer will assess your cylinder during the free survey and confirm whether it needs replacing.

Can a heat pump heat water to the same temperature as a boiler?

A heat pump typically heats water to 45 to 55°C, compared to 65 to 70°C for a gas boiler. This is sufficient for comfortable hot water and space heating in most UK homes. The system runs a weekly legionella safety cycle that briefly raises the temperature to 60°C automatically.

Will I run out of hot water with a heat pump?

Not with a correctly sized system. Your OVO surveyor will specify the right cylinder size for your household to make sure you have enough hot water for your typical daily use.

Every home is different, so the best way to get an accurate cost is to talk to us directly. OVO's heat pump experts are on hand to help — just get in touch for a free quote