Brave the cold weather with a Cosy heat pump
Do heat pumps work in cold weather?
When the temperature plummets (along with our motivation to venture outside), most of us just want to be tucked up on the sofa – cup of tea in hand, telly on, and a bottomless supply of biscuits nearby. Thankfully, unlike us, heat pumps are perfectly happy in the cold.
Contrary to myth, modern heat pumps can still extract heat from the air and work brilliantly in temperatures as low as -20°C. And while it’s rare for the UK to dip that low, it’s reassuring to know your new heating system won’t get frostbite.
Don’t believe us? We’re glad in a way. Because, in a moment of madness, our Social Media Manager decided to jump into a freezing chamber to prove it to you. And he’s really hoping this video wasn’t a total waste of time.
The heat pump experiment
Meet Xander, our Social Media Manager turned mad scientist.
His mission? To test the limits of our Cosy heat pump by stepping into a freezing chamber alongside it. He even bet his moustache on how long he could last. Bundled in more layers than an onion (and armed with questionable optimism), he’s now officially the human benchmark for cold-weather comfort. Don’t try this at home kids …
(or open it on YouTube)
A few takeaways
❄️ Our heat pump extracts heat even from freezing air
❄️ Cosy consistently maintains a warm environment
❄️ It gives any gas boiler a run for its money in extreme conditions - it’s cheaper to run too!
Now for a bit of smart tech science
We cornered TJ, one of our renewable heating experts, to pick his brain on all things heat pumps – from how they work and how efficient they are, to how they handle the cold (and what those mysterious defrost cycles actually do).
How does a heat pump work in winter?
How do air source heat pumps like Cosy keep your home warm in winter?
TJ: Heat pumps work the same way a refrigerator does. Most of us think of our refrigerators as something that makes things cold, which is the ultimate result of their work. But a refrigerator is actually just a heat pump–one that extracts the heat from the air inside and pumps it out into our homes (that’s why the back of your refrigerator is warm).
Air-source heat pumps for your home do the same thing. They extract heat from the air outside and pump it inside through your radiators. The key is the refrigerant: a special chemical that can boil even at very low temperatures. That means even when it feels cold outside to you and me, (say -20°C) the air temperature is still hot enough to boil the refrigerant in your heat pump.
That boiling action soaks up a bunch of heat energy. Then through the magic of valves and a compressor, the refrigerant temperature soars up to 65°C and gives up its heat to your radiator water. Then the cycle repeats. It’s not magic, but at times it seems pretty close!
What about the heat pump efficiency in cold weather?
Does the cop of a heat pump decrease as the weather gets colder, and the heat pump has to work harder?
TJ: True. The reason is because of that compressor I mentioned earlier. It has to work harder to cool the refrigerant below that outdoor temperature and then to compress it back to a much higher temperature. So the COP drops. But it’s worth nothing that the COP is still 2-3 times higher than a gas boiler in the same conditions. And COP is also an instantaneous measure. What matters is your SCOP–your seasonal COP–which reflects your heat pump’s awesome efficiency over the whole year.
🧠 Did you know ...
Scandinavia is one of the coldest regions in Europe, yet Norway, Sweden, and Finland have some of the highest adoption rates of air source heat pumps. If they’re trusted in -20°C winters, you can be confident they’ll work here in the UK.
PRO TIP: If you're curious about smart tech like Cosy, here's a link to more air source heat pump science.
What about built-in winter features?What's the deal with the defrost cycle?
TJ: Great question. Why does a heat pump need to defrost? Sounds odd. Recall the part about boiling the refrigerant even when the air is cold. As the outside air approaches 0°C, the refrigerant entering the evaporator (that big metal-finned radiator at the back) will be below the freezing point of water. That’s because it needs to pick up all that heat from the outside air that’s just above freezing and boil off. Since the refrigerant is below 0°C, so is the surface of the evaporator. That means little water droplets will start to freeze on the surface. Fortunately, heat pumps solve this problem easily by occasionally stopping the heating cycle for about 5 minutes and running in reverse, using hot refrigerant to melt the ice on the evaporator (it makes a satisfying hiss and steams a bit). Then it’s back to heating the home, or making hot water.
How do you keep the water in the heat pump from freezing if it’s not running?
TJ: Our Cosy has built-in frost protection. When the outside temperature falls below 7°C, our heat pump will periodically run its circulating pump to cycle a bit of warmer water from the home through the internal pipework. This only happens if your heat pump is in standby or off. If your heat pump is producing heat for your home, this protection feature doesn’t come into play. However, if it’s cold enough to risk your heat pump freezing you should definitely have your heating set to a safe temperature (we recommend 15°C minimum) to ensure nothing in your home freezes or is otherwise damaged.
🧠 Did you know ...
Even in colder months, air source heat pumps remain more efficient than traditional boilers. With efficiencies ranging from 200% to 400%, they produce two to four times more heat than the electricity they use.
PRO TIP: Check out how you can get the best out of a heat pump during the winter months.
Can an air source heat pump keep my whole home warm?
TJ: Yes, when sized and installed correctly, an air source heat pump provides steady, reliable heating for your entire home, even in the coldest UK weather. The key is to remember that your heat pump is just one component of the total heating system. Heating your home effectively requires properly sized radiators that can put enough heat into your home to overcome the heat loss in each room. Underfloor heating is especially effective in this respect because there’s so much radiative surface area. The simple answer is yes, but the better question is whether your home’s heating system is designed to.
What impact does cold weather have on a heat pump running costs?
TJ: Just like a boiler, heating your home will cost more when the weather is very cold. Your heat pump will work harder to make hotter water at a higher total output and run for longer to compensate for your home’s increased heat losses when the air is particularly frosty.
Cosy comfort, even on Britain’s frostiest days
Safe to say our Cosy heat pump is ready for whatever the UK weather throws at it! The best bit? It’s packed with smart features – updating regularly just like your phone, and when paired with the right tariff, it can lower your heating costs! Cosy heat pump customers on the Cosy Octopus tariff saved an average of £200 last year compared to using a gas boiler running at 85% efficiency on our standard variable tariff.
Cold weather energy saving tips
It's that time of the year again...
Meet Cosy: the star of the show
Our very own air source heat pump.
Hear it straight from customers
Our customers reviewed their experience with Cosy.
Cosy heat pump customers on the Cosy Octopus tariff saved an average of £200 last year compared to using a gas boiler running at 85% efficiency on our standard variable tariff
This figure is based on the actual energy consumption of all Cosy heat pump customers on a Cosy Octopus tariff between 1 July 2025 and 1 July 2026, using tariff rates at the time.
We compared this to the cost of producing the same amount of heat with a gas boiler operating at 85% efficiency, priced using our Flexible Octopus (standard variable) tariff at the same time.
Savings from gas standing charges were included only for customers who had fully removed their gas supply (less than 3% of customers). Actual savings vary depending on system design, tariff choice, home insulation, and energy use.
Our typical heat pump price is £4,459, which is lower than the national average of £5,600
This is the median post-survey price from all of our heat pump quotes after the £7,500 Boiler Upgrade Scheme has been applied, between 01/09/2025 and 28/02/2026. The national average is taken from the Boiler Upgrade Scheme statistics: April 2026 – median cost of installation Q4 2025.
Cut carbon emissions by 82% with a heat pump
This is the typical reduction in heating carbon emissions using an electric powered heat pump compared to a gas boiler.
The carbon breakdown
Gas CO2 (tonnes per year) - 2.42
Electricity CO2 (tonnes per year) - 0.43
Carbon saving (tonnes per year) - 1.99
Data sources and assumptions
Gas Energy Usage (kWh) 11500 (Ofgem medium use gas usage (Jun 2026))
Heat Pump Efficiency 312% (typical seasonal coefficient of performance from a fleet of Octopus high temperature heat pumps)
Gas Boiler Efficiency 85% (The typical gas boiler efficiency from a BEIS study)
Gas fuel emissions of (gCO2/kWh) 210 (SAP 10.2)
Electricity fuel emissions of (gCO2/kWh) 136 (SAP 10.2)
Based on these sources, heat pumps typically produce lower operational emissions when heating the home than gas boilers.
For more information, explore our Octopus Cosy heat pump fleet performance dashboard.
We're the largest heat pump installer on the Boiler Upgrade Scheme
Based on Octopus benchmarking against Ofgem reports from 2024, and we've continued to grow since.
Our customers love their heat pumps!
- 93% of people say it's the same or more comfortable than their previous boiler
- 87% say it costs the same to run or less
- 83% say it's the same noise or less than the previous boiler
- 90% say it's just as easy or easier to maintain
We survey all our heat pump customers 3 months post-installation to see how they find their heat pump compared to their previous gas boiler. Survey results are taken from a sample of 2,837 customers:
Comfort: 93% of people say it is the same or more comfortable than their previous boiler.
Running Costs: 87% say it costs the same to run or less.
Noise: 83% say it is the same noise or less than the previous boiler.
Maintenance: 90% say it is just as easy or easier to maintain.
A heat pump is around 4x more efficient than a gas boiler
Heat pumps don't generate heat by burning fuel. Instead, they transfer existing heat into your home. This means they can deliver multiple units of heat for each unit of electricity used.
Based on performance data from a fleet of installed Octopus Cosy heat pumps, typical real-world seasonal performance (SPF or SCOP) is around 3.6. This means around 3–4 kWh of heat is delivered for every 1 kWh of electricity used (an effective efficiency of 300–400%). By comparison, typical UK domestic gas boilers operate at around 85% efficiency, delivering approximately 0.85 kWh of heat per 1 kWh of gas used. On this basis, a heat pump can be around 4× more efficient than a typical gas boiler.
All our heat pumps are independently tested by the Building Research Establishment (BRE), with SCOP values published on the Microgeneration Certification Scheme (MCS) product database. Actual efficiency will vary depending on the property, system design, and usage. For more information, explore our Octopus Cosy heat pump fleet performance dashboard.
The UK's most awarded energy supplier
We've won more awards for customer service than anyone else.
Heat pumps give reliable, consistent heating and hot water
The heat pump user survey report by Nesta from May 2023 summarises that "users are highly satisfied with their heat pumps". It states: "People living in England, Scotland and Wales who own their home and use a heat pump to heat it are satisfied that heat pumps are safe, reliable, quiet heat sources that are effective for space heating and producing hot water." Find the full report here.
The Cosy heat pump is quiet
Heat pump sound power levels are verified by an independent, third-party laboratory as part of the testing process for inclusion on the MCS product database. The laboratory verifies the sound power on the A-weighted decibel curve, as A-weighting closely aligns to how humans perceive "loudness".
All heat pumps are measured using EN14511 standards to ensure uniformity across manufacturers and models. Our Cosy 6 heat pump has a verified sound power level lower than many other heat pumps of the same capacity.
Heat pump heating makes the air healthier in your home
Homes with a heat pump emit far less harmful nitrous oxide (NOx) emissions than those with gas boilers and cookers, significantly reducing asthma and other respiratory illnesses. According to the Sustainable Markets Initiative Cleantech Homes report.
A heat pump can add thousands to your property value
Analysis by the Department of Land Economy at the University of Cambridge suggests a 16% value uplift for new-build homes with enough solar and battery storage to eliminate energy bills. A further study of over five million existing properties indicates a 2-3% value increase for existing homes with solar panels or heat pumps (versus like-for-like gas-heated homes), according to the Sustainable Markets Initiative: Cleantech Homes report, 2024.
As of April 2025, the average house price in the UK is £265,497 according to the Land Registry. Therefore, a 2-3% value increase for an average house priced at £265,497 would be between £5,310 and £7,965.
Heat pumps typically last longer than gas boilers
The expected lifespan of a typical gas boiler is 10–15 years. A heat pump typically has a lifespan of 15–20 years, with UK government research indicating an average of around 20 years. Manufacturer Daikin reports similar ranges. Actual lifespan depends on factors such as installation quality, maintenance, usage patterns, and operating conditions.
Published on 29th September 2025 by:
Laura Iancu
SEO for Clean Energy