Heat pump efficiency explained: Everything you need to know before you switch

Key takeaways

• Heat pumps use smart tech to deliver 3-4 times more heat for every bit of electricity you use. That means lower bills and a smaller carbon footprint.
• COP and SCOP numbers aren’t just tech talk, they show how well your heat pump will keep you cosy and save you money. COP gives you a snapshot of efficiency, while SCOP gives a seasonal average that helps predict year-round savings and performance.
• Getting your heat pump installed right, with good insulation and the right setup, makes all the difference. Plus, adding solar panels means even bigger savings and greener heating.

Thinking about ditching your gas boiler? You’ve probably heard that heat pumps are more energy efficient. And better for the planet. But what does that really mean day-to-day? And how do you know if those efficiency stats like COP and SCOP will actually translate into lower bills and reliable heating in your home?

Let’s break it down. No jargon, just the stuff that matters.

What does “efficiency” mean for heat pumps?

Heat pump efficiency isn’t just about lower energy bills (though that’s a major benefit). It’s about how well your system turns electricity into heat energy. And, unlike boilers, which burn fuel to create heat, heat pumps use a little bit of electricity to move it from one place to another, making them incredibly efficient.

For every unit of electricity used, a heat pump can typically deliver three to four units of heat. You’ll often see that described as 300-400% efficiency.

It doesn’t mean the heat pump has created energy from nowhere. It means most of the energy warming your home has been collected from the outside air rather than bought as electricity.

How efficient are heat pumps?

A heat pump delivering three units of heat for every unit of electricity has an efficiency of 300%. Deliver four units, and that rises to 400%.

Those figures aren’t guaranteed for every minute of the year. A heat pump’s performance changes as outdoor temperatures rise and fall, while producing hot water will usually require more energy than gently warming your rooms.

The design matters too. A heat pump connected to suitable radiators and set up to run steadily with lower-temperature water will usually perform more efficiently than the same model in a poorly designed system.

COP and SCOP explained

Heat pump efficiency is usually described using two figures: COP and SCOP.

What is COP?

COP stands for Coefficient of Performance. It tells you how efficiently your heat pump is working at any given moment.

Say your heat pump has a COP of 4. That means for every 1 unit of electricity it uses, you get 4 units of heat.

COP changes depending on things like the outdoor temperature, your heating system's flow temperature, and how well your outdoor unit is performing. Lower flow temperatures (the temperature of the water your heat pump sends to your radiators or underfloor heating) usually mean better efficiency.

Why does COP matter? Because it shows you how your heat pump turns electricity into heat. And where you might be able to get more out of your system.

What is SCOP?

While COP shows efficiency at a moment in time, the SCOP (Seasonal Coefficient of Performance) takes a step back and looks at the bigger picture. It accounts for seasonal temperature differences and gives you an average performance score across the entire year.

SCOP is particularly helpful when comparing the performance of different types of heat pumps – from air source heat pumps (like the Aira Heat Pump) to ground source heat pumps – under real-world conditions. If you live in a colder climate or have a longer heating season, SCOP provides a more accurate idea of year-round efficiency.

The higher the SCOP, the more efficient your heat pump is year-round. And with the right setup, like underfloor heating or larger radiators, you can get even more out of it by running at lower flow temperatures.

Let’s talk about a real-world measure of efficiency: SPF 

COP and SCOP are useful comparison tools, but neither shows exactly how a complete heat pump system has performed in someone’s home. COP is a snapshot, while SCOP is a standardised estimate of a heating season.

SPF, or Seasonal Performance Factor, looks at measured performance over time. It compares the heat the system has delivered with the electricity it has actually used:

Total heat delivered ÷ total electricity used = SPF

An SPF of 4 means the system delivered four units of heat for every unit of electricity over the measured period.

Why we use SPFₕ4

More precisely, for our Aira Heat Pump performance, which you can see live on our dashboard, we use SPFₕ4. The little “h” stands for heating, while the “4” describes what’s included in the measurement – not the efficiency score.

SPFₕ4 counts the heat delivered for space heating and hot water, then compares it with the electricity used by the heat pump and wider system, including:

• Defrost cycles
• Built-in circulation pumps and controls
• Standby and idle operation
• Integrated backup heating, if it’s used

This gives us a more realistic efficiency figure because it counts the electricity used by the whole heating system – including the less obvious bits like defrosting, standby and circulation pumps.

SPF is normally measured across a heating season or full year. At Aira, we apply the same SPFₕ4 boundary to monthly data across the wider Aira Heat Pump fleet – not a handful of best-performing homes. This shows how our systems perform as real UK weather and heating demand change.

When is a heat pump most efficient?

Heat pumps are happiest when they don’t have to make a big jump in temperature. The milder it is outside, and the less hot the water needs to be, the less electricity the system uses to keep your home warm.

While you can’t do much about the British weather, a well-designed system can keep the water temperature lower while still keeping every room comfortable – helping your heat pump run smoothly and efficiently.

1. When the water temperature is lower

The water travelling from your heat pump to your radiators or underfloor heating has a rather unexciting name: the flow temperature. With a heat pump, cooler is generally better—as long as every room stays warm.

Many boiler systems blast very hot water around the home in short bursts. A heat pump takes a gentler approach, sending warm water around for longer so it can steadily replace the heat your home loses.

This isn’t about settling for a colder home. It’s about designing the radiators, pipework and controls so the water doesn’t need to be piping hot to keep every room comfortable.

2. When it can run steadily

Heat pumps don’t love stop-start heating. They’d rather tick along steadily, maintaining a comfortable temperature instead of reheating a cold home from scratch.

Modern controls make that easy. As the weather becomes milder, they lower the water temperature. When it gets colder, they raise it enough to keep your home warm—all without you constantly fiddling with the settings.

3. When it’s the right size for the home

Bigger isn’t automatically better. If a heat pump is too large, even its lowest setting may produce more warmth than the home needs, forcing it to keep switching on and off. This is called short cycling, and it can reduce efficiency and place unnecessary strain on the system.

Go too small and the heat pump may struggle when the weather turns cold, relying more heavily on extra electric heating. A room-by-room heat loss calculation takes away the guesswork and shows your installer which size fits the home.

Read our guide to heat loss calculations to see how we work that out.

What affects heat pump efficiency?

The weather and the temperature of the water have the biggest direct effect on efficiency. But a heat pump doesn’t work alone—the rest of the heating system can make its job easier or much harder.

• Your radiators or underfloor heating: The more heat they can release into a room, the less hot the water needs to be. That means less work for the heat pump.
• How well your home holds on to heat: Good insulation and windows slow down heat loss, so the system has less warmth to replace.
• The system settings: Smart controls can turn the water temperature up or down with the weather, instead of running hotter than needed all year.
• Your hot water use: A cylinder needs hotter water than your radiators usually do, so the heat pump works harder while preparing hot water. That’s completely normal.
• How the system is installed and looked after: Water needs to move freely, radiators need to be balanced and the outdoor unit needs room to breathe. Get those details right and the whole system runs more smoothly.

The heat pump is only one part of the picture. Bring the heat pump, radiators, pipework and controls together as one system designed around the home, and every part can do its job properly.

Are heat pumps efficient in cold weather?

Yes. Cold air still contains usable heat. Even when the temperature drops below zero.

The colder it gets, the harder the heat pump has to work to bring that warmth into your home. From time to time, it will also run a short defrost cycle to clear ice from the outdoor unit. That’s completely normal.

All that extra work means its COP will usually be lower on a freezing day than on a mild one. But lower efficiency doesn’t mean no efficiency – or no heating. A correctly sized system is designed to keep your home warm through the cold UK weather.

Good installers will also use local winter weather data when designing the system, rather than one average temperature for the whole UK. So the British cold isn’t a surprise. It’s already part of the maths.

Read more about how heat pumps work in cold weather.

Heat pump efficiency compared with a gas boiler

This is where heat pumps really pull away from boilers. Put one unit of bought energy in and look at how much useful heat comes out:

A boiler burns gas to create warmth, losing some energy along the way. A heat pump uses electricity to move warmth that’s already outside, which is why it can deliver three or four units of heat from one unit of electricity.

No magic. Just a much more efficient way to heat a home.

How efficiency translates to cost savings

It's simple. The better the efficiency, the lower your energy bills.

Heat pumps use less electricity to deliver the same or more units of heat compared to gas boilers, especially when running at optimal flow temperatures.

Yes, the upfront costs can be higher than traditional heating systems. But when you factor in the long-term savings and government grants (like the £7,500 Boiler Upgrade Scheme), the additional cost pays off.

Let's break it down:

So, higher efficiency means the heat pump needs less electricity to produce the same amount of warmth. That’s good news for running costs, but it isn’t the only part of your bill.

Your final energy bill also depends on:

• Your electricity tariff

• The heating system you’re replacing

• How much heat your home loses

• The temperature you keep your rooms at

• How much heating and hot water you use

• How well the system has been designed and set up

That’s why savings differ from home to home. A good installer should base any estimate on your property, tariff and expected use – not one headline figure for everyone.

Do solar panels make a heat pump more efficient?

The short answer is no. The better answer is that they can still make a brilliant team.

Solar panels won’t change your heat pump’s COP or make it produce more warmth from each unit of electricity. What they can change is where some of that electricity comes from.

When the sun is shining and your heat pump is running, it can use electricity generated on your own roof instead of buying all of it from the grid. Add a home battery and you can store spare solar electricity during the day, then use more of it later.

That can reduce your grid use and energy bills, but the result will depend on the size of the system, the weather, your tariff and when your home uses energy.

What are the benefits of combining heat pumps with solar panels?

1. Slash your running costs: Solar panels power your heat pump during the day, cutting your electricity bills and keeping your home cosy for less.
2. Boost your efficiency: Solar energy feeds your system clean power when you need it most. That means less pulling from the grid and more smart saving.
3. Shrink your carbon footprint: Clean solar energy plus a heat pump equals heating with zero emissions. Better for your home, better for the planet.

How Aira keeps your heat pump performing efficiently

Efficiency isn’t something you add after installation. It has to be designed in from the start.

That starts with your free home energy assessment, where one of our Clean Energy Experts looks at your home and talks through your heating needs. Before installation, we carry out a detailed technical survey and use our bespoke software to design the system room by room.

We use that information to choose the right heat pump output, check which radiators can stay and work out the water temperature needed to keep every room warm. Our Aira technicians then install, commission and test the complete system before handing it over.

And we don’t disappear once the installation is finished. Aira Intelligence quietly adjusts your heating and hot water around the weather and your comfort settings. With a compatible electricity tariff, it can also respond as prices change.

Through the Aira all-inclusive plan, your heat pump is also monitored in the background. If something doesn’t look quite right, we can often spot it early and fine-tune the system remotely. If we need to visit, repairs, parts and labour are covered by the plan.

Better still? The first year is included with every Aira Heat Pump.

Designed properly. Installed properly. Quietly looked after. Just the way heating should be.