Suffolk home achieves exceptional 4.5+ SCOP
From heating muddle to award-winning efficiency: Suffolk home achieves exceptional 4.5+ SCOP
Overview
When Anwar and Victoria, relocated from London to rural Suffolk in early 2024, they found their new 1930s house was heated by an electric boiler that was very expensive to run. To keep costs down, they avoided using the heating altogether, relying instead on multiple layers to get through the winter.
Working with Jon Miles, from Viessmann ViPartner installer Sun-Lite Group, a Viessmann Vitocal 150-A Compact 10 kW air source heat pump (ASHP) with integral domestic hot water (DHW) cylinder was installed. The installation transformed both running costs and comfort, resulting in the property consistently achieving a measured seasonal efficiency (SPF) or Heat Pump Monitor platform Seasonal Coefficient of Performance (SCOP) of 4.55. This places the property among the UK’s top-performing monitored heat pump installations listed on the independent, open-source energy monitoring platform, Heat Pump Monitor. Between July 2024 and 1st December 2025 the system has used just £632 of electricity to generate the same heat (19,246 kWh) that would have cost £5,196 with the previous electric boiler.
The challenge: Quality infrastructure, unaffordable running costs
The property was extended by the previous owners in 2019. Though completed to a high standard, with new radiators and a comprehensive underfloor heating network installed throughout, the choice to power the system with an electric boiler created a significant problem. With the rise in the cost of electricity, running the heating became prohibitively expensive.
As a result, the heating remained switched off when the new owners moved in.
With the heating infrastructure already in place, the property was well positioned for a heat pump retrofit that could finally utilise the existing radiators and underfloor heating as originally intended.
The solution: Open loop design with full weather compensation
Sun-Lite Group approached the installation as an opportunity to implement best-practice heat pump design principles. The project proved a significant learning experience for installer Jon Miles, involving detailed U-value calculations for the property's varied construction, vaulted ceiling considerations, and verification of the underfloor heating using thermal imaging cameras after discovering no plans were available for the system.
The installation team opted for a Viessmann Vitocal 150-A Compact 10 kW air source heat pump with integral 190-litre DHW cylinder. The all-in-one design is designed to keep plumbing simple and costs down compared to buying a separate heat pump and cylinder, while the compact units look tidy inside and out.
With the outdoor unit visible from the road, appearance mattered. The Vitocal 150-A Compact’s clean lines suit the countryside setting, and its advanced acoustic design (AAD) means it runs quietly – at 56 dB(A), it's no more audible than a fridge. In such a peaceful location, this was essential for both the homeowners and their neighbours. The system provides cooling as well as heating and can reach flow temperatures of 70°C even when it's -10°C outside, though the installation was designed to run much cooler for maximum efficiency.
Full weather compensation was installed, although the homeowners were initially sceptical about this approach as they were used to conventional zoned heating controls. As a compromise, thermostatic radiator valves (TRVs) were left fitted to the two upstairs bedroom radiators to provide manual temperature adjustment if required. In practice, these have proven unnecessary – the Viessmann weather compensated system maintains comfortable temperatures throughout the property without intervention.
The system was configured with a low design flow temperature of 35°C at an outdoor design temperature of -2°C, while the DHW target temperature was set at 52°C. Viessmann's weather compensation system allows the heat pump to adjust its output smoothly in response to changing outdoor temperatures – this maintains consistent comfort and minimises electricity consumption.
The results: Award-winning performance and dramatic cost savings
Monitoring of this system on HeatpumpMonitor.org began in July 2024. Between this time and December 1st 2025, the system achieved an SPF or Heat Pump Monitor platform SCOP of 4.55. To put this into perspective, the Heat Pump Monitor platform average is 3.8, while the installer guidance threshold under the Microgeneration Certification Scheme (MCS) to access the government's Boiler Upgrade Scheme is 2.8.
This efficiency translates directly into substantial cost savings. Between July 2024 and 1st December 2025, the heat pump consumed 4,114 kWh of electricity to generate 19,246 kWh of heat at a cost of just £632. Generating the same heat with the previous electric boiler would have cost £5,196, meaning the heat pump has been more than eight times cheaper to run.
Comfort and convenience transformed
Beyond the impressive efficiency figures, the installation has transformed how the homeowners live. They report that every room now maintains a comfortable ambient temperature at all times – a stark contrast to the previous arrangement of selective heating and reliance on a log burner. The underfloor heating throughout the ground floor operates as originally intended to provide even, comfortable warmth without the cold spots and temperature fluctuations of the old system.
Homeowner, Anwar describes the installation, “It’s the best investment we have ever made! We saw immediate improvements in comfort and day-to-day living, and we couldn’t be happier with the results.”
The installation also demonstrates the advantages of the Vitocal 150-A Compact all-in-one design. With the integral 190-litre cylinder, the couple says it has ample hot water storage and the compact indoor unit fits neatly into the available space. The system delivers heating and hot water without dominating the property's utility areas.
Proving heat pump potential
This installation shows what can be achieved when quality heat pump technology meets thoughtful system design and expert installation. The combination of the Viessmann Vitocal 150-A Compact technical capabilities – including its wide modulation range of 2.1 to 14.9 kW, weather compensation system and environmentally responsible R290 refrigerant with a Global Warming Potential (GWP) of just 0.02 – with Sun-Lite Group's commitment to best-practice design principles has delivered a system that is saving money and performing to the customers’ highest expectations.
The results challenge common misconceptions about heat pump performance and running costs. Even in a period property with extensions of varying ages and construction standards, a properly designed heat pump system can achieve efficiency levels that make it substantially cheaper to run than conventional heating – all while delivering superior comfort and environmental benefits.
