Heat Pumps Run Better in Cold, Boosting Savings

Heat pumps are most efficient in colder outdoor temperatures, delivering a substantial boost in Seasonal Performance Factor (SPF) when properly commissioned.

A new analysis of thousands of UK installations shows that real‑world heat pumps often fall short of their design SPF, but the gap can be closed by tweaking commissioning practices. The study, which pulls data from the open‑source HeatPumpMonitor.org platform, found an average SPF of 3.86 across the fleet, while the median sits at 2.7‑2.8 – a difference that can be largely addressed with the right steps.[^1][^2]

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The performance gap: real data vs. textbook claims

Manufacturers typically quote SPF values of 4‑5 for air‑source units, yet field data tells a different story. The CIBSE Journal’s deep‑dive reports an average SPF of 3.86, and the self‑build guide notes a median of 2.7‑2.8 for most UK homes.[^1][^3] The discrepancy stems largely from sub‑optimal commissioning – for example, oversized compressors, high flow‑water temperatures, and control strategies that force the pump to work harder than necessary.

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Why colder outdoor air improves SPF

Heat‑pump efficiency is governed by the temperature lift between the source (outside air) and the sink (indoor heating water). When the outside air is colder, the refrigerant can absorb more heat per unit of work, raising the Coefficient of Performance (COP) and, over a season, the SPF. The tado° blog explains that modern units can achieve SPF values ranging from 2.6 to 5.4, with the upper end only reachable when the system runs at low flow temperatures (typically 35‑45 °C) and the outdoor temperature stays below 10 °C.[^4]

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Commissioning actions that lift SPF

1. Set low flow‑water temperatures – Reducing the heating water set‑point can noticeably raise SPF.
2. Right‑size the compressor – Matching capacity to the building’s heat loss improves steady‑state operation.
3. Optimize control algorithms – Smart thermostats that anticipate demand and modulate speed keep the compressor in its most efficient range.
4. Properly charge refrigerant – Correct charging avoids performance loss; a certified MCS installer ensures the proper charge.

Research highlighted by Jan Rosenow indicates that applying these measures across a large dataset can raise average SPF substantially, demonstrating the impact of good commissioning.[^5]

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Policy backdrop: the UK Boiler Upgrade Scheme (BUS)

Heat‑pump installations eligible for the BUS must be carried out by an MCS‑certified installer, ensuring a baseline of quality. The scheme currently offers up to £7,500 off air‑to‑water heat‑pump installations, encouraging homeowners to adopt low‑carbon heating while meeting the government’s decarbonisation targets.[^6][^7]

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What it means for Israel

Israel’s residential electricity tariff sits at roughly ₪0.48 /kWh. Improving SPF through proper commissioning can reduce the amount of electricity a heat pump needs, lowering annual energy costs. Because many Israeli households already install rooftop solar (average yield ~1,700 kWh/kWp/year in the central region), pairing a well‑commissioned heat pump with a solar array can cover a large share of that electricity, further cutting grid reliance and CO₂ emissions (≈0.5 kg CO₂ avoided per kWh). The synergy mirrors the UK’s push for higher‑efficiency heat pumps and illustrates how rigorous commissioning can make low‑carbon heating financially attractive in Israel as well.

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Outlook: closing the gap worldwide

The UK data proves that the efficiency gap is not a hard limit but a commissioning issue. As more installers adopt the low‑flow, right‑size, smart‑control recipe, average SPF is expected to move closer to the theoretical 4‑5 range. For Israel, where solar‑plus‑heat‑pump systems are gaining traction, the lesson is clear: invest in certified installers and rigorous commissioning to reap the maximum energy and cost savings.

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Sources

[^1]: CIBSE Journal – Bridging the heat pump efficiency divide [^2]: ScienceDirect – Open‑source insights into UK heat pump performance gaps [^3]: Self‑build – Understanding heat‑pump performance [^4]: tado° Blog – Heat pump efficiency: why 400% is possible [^5]: Jan Rosenow on LinkedIn – 40% higher efficiency [^6]: MCS – Boiler Upgrade Scheme for installers [^7]: Ofgem – Boiler Upgrade Scheme guidance for installers [^8]: pv magazine – Lower temperatures, higher heat pump efficiency

Sources & further reading

• Bridging the heat pump efficiency divide - CIBSE Journal
• Bridging the efficiency divide: open-source insights into UK heat pump performance gaps - ScienceDirect
• [PDF] Heat pumps and UK's decarbonisation: lessons from an Ofgem dataset of...
• Heat pump efficiency: why 400% is possible | tado° Blog
• An Expert Explains How to Understand Your Heat Pump's...