Heat Pump Efficiency UK: What’s Normal and How to Check

Heat Pump Efficiency UK: What’s Normal, What’s Poor, and How to Check Yours

You’ve probably heard that heat pumps are “300% efficient”. Then the electricity bill arrives and it doesn’t feel that way. Both things can be true. A heat pump really can deliver three or four times more heat than the electricity it uses, but only when the system around it is designed and set up properly.

This guide explains what heat pump efficiency means, what a good figure looks like in a UK home, what drags it down, and how to check your own.

The Short Answer

A well designed and properly tuned air source heat pump in a UK home typically delivers around 3 to 4 units of heat for every unit of electricity over a year. Many real installations do worse, usually because of settings and system design rather than the heat pump itself. If your seasonal figure is well below 3, there’s normally something to find.

What “Efficiency” Means for a Heat Pump

A heat pump doesn’t create heat from electricity the way a heater does. It moves heat from the outside air into your home, which is why it can deliver more heat than the electricity it consumes.

Two numbers describe this:

• COP (coefficient of performance) is a snapshot. A COP of 3 means 3 kWh of heat for every 1 kWh of electricity at that moment.

• SCOP or SPF (seasonal performance) is the average across a whole heating season. This is the figure that really decides your bills.

Our guide on what COP and SCOP mean goes deeper on the terms. That’s where “300% efficient” comes from: a COP of 3 is 300% when written as a percentage.

What’s a Good Efficiency Figure?

Manufacturers publish rated efficiency figures, but they’re measured in lab conditions, usually at mild outdoor temperatures and low flow temperatures. Real homes tend to do worse. UK field trials have reported average seasonal performance for air source heat pumps a little under 3, with a wide spread between the best and worst installations.

As a rough guide, not an official standard:

What Affects Heat Pump Efficiency?

These are roughly in order of how much difference they make.

1. Flow temperature. This is the single biggest lever. The lower the water temperature the heat pump has to produce, the less work it does. A commonly quoted rule is that each degree you can lower the flow temperature improves efficiency by around 2% to 3%. In one of our cases, a family’s bills doubled because the heat pump was running at 55°C in mild weather. The unit was fine. The setting wasn’t.

2. Weather compensation. This automatically lowers the flow temperature as the weather gets milder. If it’s off or badly set, the system runs hotter than it needs to. Our guide on how to set weather compensation shows how to check it.

3. Zoning and stop-start running. Heat pumps do best when they run steadily. Too many zones, or schedules that keep switching the system on and off, push efficiency down. A new build in Essex with nine underfloor zones was running at a COP of 1.2 until the zones were cut to two and the flow temperature lowered.

4. Sizing. An oversized unit cycles on and off, and an undersized one leans on backup heating. Both cost efficiency. See what happens if a heat pump is oversized and the signs of an undersized one.

5. Hot water. Heating water to a usable temperature takes a higher flow temperature than heating radiators, so hot water is generally less efficient. A boost setting or frequent high temperature cycles can quietly add a lot of electricity. Our guide on what temperature your hot water should be set to covers it.

6. Electric backup and immersion heaters. Electric heating gives 1 unit of heat per unit of electricity, against 3 or 4 from the heat pump. If a backup heater or immersion is running more than it should, efficiency drops fast.

7. Radiator and emitter size. If radiators are too small, the system has to run a higher flow temperature to heat the room, which lowers efficiency across the board.

8. Installation quality and maintenance. Poorly insulated external pipework, a blocked strainer or filter, and low flow rates all cost efficiency without showing up as a fault.

How Efficient Is a Heat Pump in Winter?

Efficiency falls as the outdoor temperature drops, because the heat pump has to extract heat from colder air and sometimes spends energy on defrost cycles. In freezing weather the COP may drop towards 2 or 3. That’s normal, and it’s already built into the seasonal figure.

What matters is that the system runs steadily at the lowest flow temperature that keeps the house comfortable. If it’s running constantly in cold weather, that’s often fine. Our guide on why a heat pump runs constantly explains when it’s normal and when it isn’t.

Is a Heat Pump Cheaper to Run Than a Gas Boiler?

Efficiency isn’t the same as cost. The question is how much each unit of heat costs.

• Gas boiler: gas price divided by boiler efficiency (say, 90%)

• Heat pump: electricity price divided by COP

That means the more electricity costs compared with gas, the higher your COP has to be to break even. For example, if electricity costs about 3.5 times as much as gas per unit, a heat pump needs a seasonal COP of around 3.2 to match a 90% efficient gas boiler. Below that, it costs more. Above it, it costs less. This is why a poorly tuned heat pump can cost more to run than the boiler it replaced, and a well tuned one can cost less. Our article on running costs against fossil fuels has the full comparison.

How to Check Your Own Heat Pump’s Efficiency

Measuring true COP needs two numbers: heat delivered and electricity used.

1. Check your app or controller. Many modern heat pumps show energy in and heat out, or a COP or efficiency figure.

2. Use a long enough window. A single day can be misleading. Look at a week at least, and ideally a full month.

3. Divide heat delivered by electricity used. The result is your COP for that period.

4. Be cautious with app figures. They’re often estimates, and they can differ from your meter. If you’ve noticed this, see our article on why the app and meter don’t match.

5. If your system doesn’t report heat output, you can’t know the true COP. A heat meter is the only accurate way. In the meantime, watch the signs: steady running, a sensible flow temperature, and electricity use that matches the weather.

What to Do If Your Efficiency Is Poor

In most cases the fix is settings or design, not hardware:

• Check weather compensation is on and set sensibly

• Lower the flow temperature gradually, giving the house a few days to respond

• Check that the hot water boost and any backup heater aren’t running more than needed

• Check the schedules, zones and thermostats aren’t forcing stop-start running

• Clean the filter or strainer, and check insulation on external pipework

If you’ve tried these and the bills are still high, it’s worth having someone look at the whole system. Our Fix My Heat Pump service does this on a one-to-one video call, fully remote. If the design looks like the problem, a Heat Loss & Plumbing Survey gives you the room-by-room numbers.

Frequently Asked Questions

What is a good efficiency for a heat pump?
A seasonal COP of 3 or more is generally good for an air source heat pump in the UK, and 3.5 or more is excellent. Below about 2.5 usually points to a setting or design problem.

Are heat pumps really 300% efficient?
A COP of 3 can be written as 300%, because the heat pump delivers 3 units of heat for every 1 unit of electricity. It’s possible because it moves heat from outside rather than creating it. Real-world figures vary with the system and the weather.

How efficient is a heat pump in winter?
Efficiency drops as it gets colder. In freezing weather, COP can fall towards 2 or 3, which is normal. A well designed system still performs well over the full season.

Is a heat pump more efficient than a gas boiler?
Yes, in terms of heat delivered per unit of energy. Whether it’s cheaper depends on the electricity and gas prices and on your seasonal COP.

Does flow temperature affect efficiency?
Yes, it’s one of the biggest factors. A lower flow temperature means better efficiency, as long as the house stays comfortable.

How can I improve my heat pump’s efficiency?
Start with weather compensation and flow temperature, then check zoning and schedules, hot water settings and any backup heating. If it’s still poor, a system review will usually find the cause.