Outside a 100-year-old house on the edge of the Peak District in northern England, a heat pump’s fan blades are swiftly spinning. They’re drawing outdoor air over coils of refrigerant, harvesting warmth from that air. All air-source heat pumps do this—and they can glean heat even on cold days. But this heat pump is special. It is one of the most efficient installations of its kind in the country.
“I’m number two on there,” fizzes owner Rob Ritchie, a retired chemistry teacher, referring to the system’s position on HeatPumpMonitor.org, a kind of online leaderboard for heat pumps around the UK and beyond. “I should say it isn’t important—but it is. It’s nice being there.”
At the time of writing, real-time data suggests that for every kilowatt-hour of electricity Ritchie’s heat pump consumes, it delivers 5.5 kilowatt-hours of heat—a coefficient of performance, or COP, of 5.5. Achieving a COP of 5 or above is “absolutely incredible,” says Emma-Louise Bennett, active transition support lead at Viessmann, the company that made Ritchie’s heat pump. In the UK, average heat pump COPs tend to be between 2 and 3.
For social-media-savvy plumbers and environmentally conscious home renovators who are increasingly sharing videos of their heating systems online, heat pumps are in vogue. In the race to decarbonize and curtail the devastating effects of climate change, switching home heating systems away from fossil-fuel-burning boilers and furnaces is essential. Heat pumps will be a key weapon in that fight, says the International Energy Agency. It estimates that, globally, heat pumps could reduce CO2 emissions by 500 million metric tons—equivalent to taking every car in Europe off the road.
A new generation of heating engineers has realized that they can push heat pumps to the limit. These installers are reaching astounding levels of efficiency by taking extra care to design low-temperature heating systems that warm rooms without using excess energy.
Heat pumps can offer multiple kilowatt-hours of heat per kilowatt-hour of electricity, thanks to physics. The refrigerant sealed inside the device evaporates readily when it is warmed even slightly, say by the outdoor air, and a compressor then pressurizes the warmed gas, which has the effect of heating it further. It only takes a little electricity to power this process, which can raise the refrigerant’s temperature by many degrees Celsius.
Since moving to his detached house near Sheffield about 10 years ago, Ritchie has installed loft insulation and solar panels, but the fabric of the building is not necessarily ideal for keeping the place toasty in an efficient way. The property has thin-cavity walls without much insulation in them, and Ritchie lives at 800 feet above sea level, meaning outdoor temperatures are generally relatively low. Thanks to his heat pump and solar panels, though, he estimates he’s now saving £2,700 ($3,420) on his utility bills annually. It goes to show that heat pumps can work well in older properties in challenging locations, he says.
The system was designed by local installer Damon Blakemore, who also checks HeatPumpMonitor.org regularly to see how his work stands up against that of his competitors. Ritchie’s heat pump is not quite in pole position at present, but it is noteworthy, emphasizes Blakemore, because once a year’s worth of data has accumulated this September, it could be the first air-source device on the leaderboard to achieve a 365-day seasonal COP, or SCOP, of 5. This is an average that reveals how well a heat pump has performed over an entire year. Weather changes between summer and winter, which shift demand for heating, tend to affect overall system efficiency, among other factors.
Blakemore is one of the “SCOP-chasers,” as Bennett puts it, driven to maximize the efficiency of the systems he installs. There is a small but highly visible group of such people in the UK who follow each other on Facebook and X, drop in on each other’s podcasts, and jostle for high rankings on HeatPumpMonitor.org. Among the stakeholders in this race for efficiency is Heat Geek, an organization that has trained multiple high-performing installers—including Blakemore.
“It’s not really something we particularly anticipated,” says Glyn Hudson, cofounder of Open Energy Monitor (OEM), which runs HeatPumpMonitor.org, referring to the casual competition emerging in the heating industry. “But installers are proud of their work. They do enjoy showing off photos of their installations on social media. The pipework layout is very important to them.”
There are now more than 170 heat pumps connected to the leaderboard. Most are in the UK. A high ranking can help installers sell their services to customers, adds Hudson. This is crucial because a badly installed heat pump can leave homeowners shivering or facing massive energy bills.
If you want to add your own heat pump to the online leaderboard, you need to attach a small array of temperature and electricity meters to your heating system. These record electrical input and heat output data in real time, with measurements transmitted automatically to OEM every 10 seconds. It’s possible to track your heat pump’s COP over months or even years, but the kit required isn’t exactly cheap. A typical monitoring setup could cost between £500 and £700, says Hudson, all on top of the price of the heat pump system itself.
Still, getting an idea, albeit not peer-reviewed analysis, of how well heat pumps can work in the UK is valuable, suggests Hudson—in the aggregate, the dataset could help researchers and policymakers study heat pump performance on a larger scale than before. Having access to live data also means installers can quickly spot when the devices develop faults. Tracking performance is also just fun. “It’s bonkers,” Hudson says of Ritchie’s high COP. “It’s hard to comprehend that.”
HeatPumpMonitor.org is a unique resource at present. It can be difficult to locate data on live heat pump performance. WIRED spent weeks scouring the web and speaking to experts to find examples of heat pump systems that could beat Rob Ritchie’s current SCOP and found only a handful of possible contenders.
“There are a couple of organizations that are trying to get more real-world performance data on heat pumps, but it’s tough to find,” says Kevin Kircher, who studies heat pump efficiency at Purdue University in the US.
Rewiring America, a nonprofit focused on electrifying homes and businesses, says it is working on 100 heat pump installations that it hopes, eventually, to study in terms of their efficiency. There are additional challenges in measuring heat pump performance in the US. Most US home heating systems rely on forced-air distribution, rather than the water-filled radiators common in Europe. It is easier to attach a temperature monitor to a water pipe.
Back in the UK, the independent research body Energy Systems Catapult has published data on a sample of heat pump installations, with the best ones achieving a 365-day SCOP of around 4.4.
“If you can set that standard across the whole of the UK, you’re laughing. That’s where you should be aiming,” says Harland Guscott, a plumber in the southeast of England who became vegan and switched to installing heat pumps instead of gas boilers in order to protect the environment. He says his own heat pump installations tend to reach SCOPs above 4.
Some of the key elements in achieving a high SCOP include keeping the flow temperature low; enabling weather compensation, so you don’t heat too much when it’s mild outside; adding large radiators that distribute heat efficiently into rooms; or using technology to intelligently defrost heat pumps during cold, damp weather, since that tends to make them ice up.
“We developed some algorithms that can anticipate when frost is going to go up,” says Kircher, who explains that small, proactive defrost cycles can boost overall efficiency. Bennett at Viessmann adds that the heat pump in Ritchie’s installation includes a buffer that allows it to defrost itself without interrupting indoor heating, therefore helping it to maintain room temperatures while running at a continuous, gentle pace.
Lambda, an Austria-based heat pump manufacturer, says its latest air-source models, soon to be released, could achieve SCOPs of 6 so long as they are used in properties with relatively low heating demand—a house with underfloor heating, for example, which can run on a modest flow temperature of 35 degrees Celsius.
But Lambda’s heat pumps are “not the cheapest” admits Manuel Krall, product manager: “If somebody’s not really into the topic or doesn’t know what COP means, then they will not buy us, usually.”
Lambda’s heat pumps use R290, or propane, as a refrigerant, which is considered both more efficient and more environmentally friendly than some older refrigerants on the market. R290 may also be helpful in buildings where low-temperature heating isn’t an option, since it could enable heating of radiators to say, 50 degrees Celsius, while still retaining reasonably good SCOPs.
According to Lambda’s data, one customer has been using their air-source heat pump to supply an underfloor heating system with water at 35 degrees Celsius, achieving a SCOP of 5.87 across a two-year period, though this has not been independently verified.
There are different kinds of heat pumps that are in principle even more efficient than air-source devices. Instead of absorbing warmth from the air, you can opt to harvest heat from the ground or even from bodies of water instead. Such systems tend to cost more, though.
Patrick Wheeler, director of Vito Energy, describes a recent installation that required drilling a borehole in a customer’s driveway. A fluid-filled pipe runs from the borehole up to the roof where it passes beneath solar panels to gather yet more heat—all in “one big loop,” he says.
“The end result is the most efficient heat pump system we’ve ever installed,” he adds. “We’re hoping that it’s going to finish at an annual coefficient of around 6.” Time will tell—the system has only been fully operational for about a month. And this approach is not for the cash-strapped. The installation cost £60,000, not including a new underfloor heating system.
Using water as the heat source can be especially efficient, points out Star Refrigeration, a supplier of industrial heating systems in Scotland. In one proposed design, recalls Dave Pearson, group sustainable development director, a heat pump would have used 60 degree Celsius wastewater to help it raise the temperature of fluid in a heating loop from 60 to 70 degrees. The mooted system had a theoretical COP of more than 10. “But it hasn’t been built,” says Pearson.
There is a fundamental limit on heat pump COP known as the Carnot limit, says Kircher. In short, it means that the theoretical maximum COP will always be constrained in proportion to the difference between your outdoor source of heat and your indoor temperature. The greater that difference, the lower the highest possible COP is—and then there are the inevitable efficiency losses in the system itself. The heat pump’s compressor is never going to be 100 percent efficient, for example.
Gunning for towering SCOPs and reaching towards the Carnot limit is all well and good—but obsessing over this could become distracting, stresses Wheeler. “It’s something that’s been bugging me—everyone talks about SCOP,” he says. “What we should be referencing is, what’s the cost, per square meter, for certain types of homes?”
HeatPumpMonitor.org allows users to sort the listed installations by running cost, based on various available electricity tariffs, and this changes the picture slightly, bumping Ritchie’s system down a few places, depending on what options you select.
Michael de Podesta, a retired physicist in England, has a house with solar panels, external wall insulation, and a heat pump running at a SCOP of 3.5. Although that’s not nearly as high as Ritchie’s and others’, it doesn’t really matter, because the running costs for de Podesta’s system are tiny—his annual electricity bill, for his heat pump and all other appliances, is a mere £250. That’s possible even while keeping his property at an internal temperature of 20 degrees Celsius.
Last year, de Podesta wrote a blog post entitled “COP Envy Is Pointless,” in which he explained that when a house is extremely well insulated—as his is—the heat pump’s SCOP will actually fall, because it is largely being used to heat hot water, especially in the spring and summer. Since people tend to heat their hot water to 50 degrees Celsius or more, the heat pump has to work relatively hard, albeit briefly, and its efficiency can appear stymied.
“You get this funny effect,” says de Podesta. “If you reduce the amount of space heating, which gets the better average SCOP, then the overall SCOP comes down.” Wheeler refers to this as the “summer drag” effect, and it’s one reason why fixating on SCOP values can be misleading.
But the rivalry between installers over SCOPs is not a waste of time, says de Podesta: “It’s healthy, good competition.”
Ritchie, for one, is enjoying the attention his high-performing heat pump has generated. He has fielded queries from many interested parties, including publications besides WIRED. “I don’t really want to be a celebrity on this,” he insists, but he’s glad to raise the profile of these systems. “I certainly would wave the flag for heat pumps. I think they’re brilliant.”