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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.