COP, SCOP and What Modern Systems Actually Deliver
Heat pump efficiency is the ratio of heat delivered to electricity consumed. Modern systems run at 300–500% seasonal efficiency, and top models like KRONOTERM ADAPT reach 622% (SCOP 6.22), while ETERA in water-to-water mode reaches 848% (SCOP 8.48). This guide explains COP, SCOP and SPF, what drives real-world performance, and how to maximise efficiency in your home.
A heat pump’s efficiency is the ratio between the electricity it consumes and the heat it delivers. Unlike a gas or oil boiler that converts fuel into heat, a heat pump moves existing thermal energy from the air, ground or water – so it can deliver several units of heat for every unit of electricity used. Theoretical efficiency measured in laboratory conditions gives the Coefficient of Performance (COP); real-world efficiency in your home across an entire heating season gives the Seasonal Performance Factor (SPF). SPF is typically lower than COP because real installations include defrost cycles, controls and parasitic energy use – that is normal, not a fault.
A heat pump does not turn electricity into heat. It uses electricity only to drive a compressor that captures existing thermal energy from the outside air, the ground or groundwater. The clearest mental model is a refrigerator in reverse: a fridge moves heat from inside to outside; a heat pump moves heat from outside to inside.
For the complete cycle walkthrough, see our complete heat pump guide.
The captured heat is at low temperature – too cold to warm the home directly. The compressor squeezes the refrigerant gas, which raises its temperature dramatically (the same physics that makes a hand pump warm up when you compress air). This is the only step that uses meaningful electricity.
In the condenser, the hot refrigerant releases its energy into the home’s heating water, feeding underfloor heating, radiators or domestic hot water. The cooled refrigerant passes through an expansion valve and returns to the outside to absorb more environmental heat. The cycle repeats continuously.
Because most of the delivered heat is “free” environmental energy, only a fraction of the total output comes from the electrical input. KRONOTERM ADAPT uses 1 kWh of electricity but delivers 6.22 kWh of heat, meaning 5.22 kWh came directly from outside air. With ETERA in water-to-water mode, the figure reaches 8.48 kWh of heat from 1 kWh of electricity.
This is why heat pump efficiency routinely sits between 300% and 850%. Independent data from the Energy Saving Trust confirms similar real-world averages for UK installations.
Heat pump efficiency is calculated as heat output divided by electrical input. Under fixed laboratory conditions this gives the Coefficient of Performance (COP) – a ratio of 5.0 means 5 kWh of heat per 1 kWh of electricity. Real-world factors lower the ideal value: defrost cycles, controls, parasitic energy and seasonal temperature swings all reduce the measured figure compared to lab tests. The Seasonal Coefficient of Performance (SCOP) accounts for this by averaging across a full heating season under EN 14825.
The Coefficient of Performance is measured under EN 14511 at a fixed test point, typically A7/W35 (7 °C outdoor air, 35 °C flow temperature). It tells you how efficient the compressor cycle is under ideal lab conditions. Useful for comparing the underlying technology of two heat pumps — but it does not predict how the unit will perform across a real winter.
The Seasonal Coefficient of Performance is the EU energy label figure. Defined by EN 14825, it averages performance across four part-load conditions (100%, 75%, 50%, 25%) and three reference climates: Warmer (Athens), Average (Strasbourg) and Colder (Helsinki). KRONOTERM ADAPT reaches SCOP 6.22; ETERA reaches 8.48.
The Seasonal Performance Factor is measured on the installed system through a real heating season. It includes everything: defrost cycles, controls, immersion top-ups, circulation pumps. SPF is typically 0.3 to 0.6 lower than the certified SCOP — that is normal, not a fault. Compared to a 90% efficient gas boiler, an SPF 4.0 heat pump uses 4.4× less primary energy per unit of heat.
Both standards ensure heat pump claims are comparable across Europe. EN 14511 defines the static laboratory tests that produce COP. EN 14825 builds on those results to model the full heating season, producing SCOP. All KRONOTERM SCOP values are independently verified through EHPA HP Keymark certification (European Heat Pump Association) and tested under TÜV protocols, ensuring the published figures (ADAPT 2 SCOP 6.22, ETERA SCOP 8.48, VERSI SCOP 4.97) match real-world field performance.
Four design and operational factors shape real-world heat pump efficiency in your home: flow temperature (the single biggest design lever), building insulation, system sizing, and source temperature. Every 1 °C reduction in average flow temperature raises overall seasonal efficiency by 2–3% — which makes underfloor heating and upsized radiators the most cost-effective efficiency upgrade you can make.
The single biggest design lever. Running at 35 °C instead of 55 °C can lift seasonal efficiency by 25–35%. Underfloor heating and upsized radiators are what make low flow temperatures possible — every 1 °C reduction in average flow temperature raises overall efficiency by 2–3% across the season.
Insulation decides how much heat a home is losing and how much electricity the heat pump uses. An older home with little or no wall insulation uses 30-40% more electricity per year than a modern house with 15-20 cm of insulation for the same indoor temperature.
A correctly sized heat pump runs long, steady cycles at the part-load where SCOP peaks. Oversizing causes short-cycling and lower seasonal efficiency. Refrigerant charge, water flow rate and hydraulic balancing must be set up by a certified installer to maintain that performance over time.
Where the heat comes from has the biggest single influence on year-round SCOP. Outdoor air swings between -10 and +25 °C. Ground at 1.5-2 m depth varies 7-15 °C seasonally. Groundwater holds a stable 7-12 °C year-round. Stable, warmer sources mean less compressor work and higher SCOP – water-to-water systems regularly reach SCOP 8+ for this reason.
Water-to-water heat pumps are the most efficient because their source temperature stays at a stable 7–12 °C all year — KRONOTERM ETERA reaches SCOP 8.48. Ground-source systems follow, with stable performance year-round. Air-to-water units are easiest to install and the most common across Europe; the best models like KRONOTERM ADAPT reach SCOP 6.22 even with outdoor air as the variable source. See the Heat Pump Association UK for industry-wide UK performance data.
| Heating system | Water-to-water heat pump | Ground-source heat pump | Air-to-water heat pump | Modern gas boiler | Oil boiler |
|---|---|---|---|---|---|
| Seasonal efficiency (SCOP) | KRONOTERM ETERA reaches 8.48 | KRONOTERM ETERA reaches 5.95 | KRONOTERM ADAPT 2 reaches 6.22 | 0.85 – 0.90 (90% max) | 0.80 – 0.85 (85% max) |
| Why this SCOP | Direct heat exchange with 7-12 °C groundwater – no brine loop, no source cooling during heating season. | Closed brine loop in vertical borehole; 8-12 °C source slightly cools during heating season – some thermal resistance. | Variable -10 to +25 °C outdoor air; R290 refrigerant and Alpine engineering maintain SCOP down to -25 °C. | Combustion physics cap efficiency at ~90% – rest lost up the flue. | Higher flue and combustion losses than gas; older underlying technology. |
Heat pump efficiency is maximised by getting four things right: correct sizing, lower design flow temperature, proper building insulation, and properly tuned weather compensation. Each is independent and they compound — together they make the difference between a heat pump that hits its certified SCOP and one that underperforms by 15–25%.
A correctly sized heat pump runs long, steady cycles at the part-load where SCOP peaks. Oversizing causes short-cycling and lower seasonal efficiency. Refrigerant charge, water flow rate and hydraulic balancing must be set up by a certified installer to maintain performance over time.
Underfloor heating or upsized radiators let the heat pump run at 35-40 °C flow instead of 50-55 °C. Every 1 °C drop in flow temperature adds 2-3% seasonal efficiency.
Set up weather compensation correctly during commissioning – a properly tuned curve lifts seasonal efficiency by 20-30% versus a fixed-flow setup. Avoid aggressive overnight setbacks; steady operation beats deep drops. Pair the heat pump with PV solar to make shoulder-season heating effectively free. Monitor real SPF with CLOUD.KRONOTERM and refine the curve over time.
Service the system annually – refrigerant charge and flow rate drift over time, and a 30-minute check keeps SPF stable. Insulate the building fabric first: lower heat loss compounds every other gain and lets the heat pump operate within its efficient range.
Premium air-to-water heat pump with SCOP up to 6.22
Water-to-water or air-to-water — the highest SCOP in the range (8.48)
Compact air-to-water for tight spaces
A heat pump’s efficiency is the ratio of heat it delivers to the electricity it consumes — modern systems run at 300–500% efficiency, and top KRONOTERM models like ADAPT (SCOP 6.22) or ETERA (SCOP 8.48) deliver up to eight times more heat than the electricity they use. Efficiency is measured as COP at a single operating point or as SCOP across an entire heating season.
Because a heat pump does not generate heat from electricity — it moves heat that already exists in the air, ground or water into the home. Electricity powers only the compressor and circulation pumps, so the system delivers three to eight times more heat than the electricity it consumes.
The difference is timing: COP measures efficiency at a single operating point in the lab, usually at 7 °C outdoor air and 35 °C flow temperature. SCOP averages efficiency across the full heating season under EN 14825, factoring in real temperature variation, four part-load conditions and parasitic energy use. SCOP is the more useful figure for predicting real running costs.
SPF (Seasonal Performance Factor) is the efficiency measured on the installed system through a real heating season. It includes auxiliary energy use like defrost cycles and circulation pumps. SPF is typically 0.3 to 0.6 lower than the SCOP rating — that is normal — and it is the figure most national grant schemes care about.
A realistic SCOP for an air-source heat pump in UK/Irish climate is between 3.5 and 4.5, with excellent systems reaching 5.0 and above. Top-tier units like KRONOTERM ADAPT hit SCOP 6.22 under EN 14825 average climate – nearly 50% above category average. The exact figure depends on flow temperature design, insulation and installation quality.
Efficiency drops as outdoor temperatures fall, but not as much as people expect. A high-efficiency air-to-water unit can deliver COP around 5.0 at +8 °C, around 3.0 at 0 °C, and around 2.0 at -5 °C — still more efficient than a gas boiler at every point. KRONOTERM units operate down to -25 °C.
Water-to-water systems are most efficient in winter because groundwater stays at a stable 7-12 °C year-round – KRONOTERM ETERA reaches SCOP 8.48 in this mode. Ground-source follows, then air-to-water. Top air-to-water models like KRONOTERM ADAPT still reach SCOP 6.22 and operate down to -25 °C, so full heating performance even in continental winters.
Lower the design flow temperature — switching to underfloor heating or upsized radiators is the biggest single lever. Improve insulation, set up weather compensation properly, avoid aggressive overnight setbacks, and schedule annual servicing. Every 1 °C drop in flow temperature raises overall efficiency by 2–3%.
Yes — significantly. A condensing gas boiler caps out at around 90% efficiency, with the rest lost up the flue. A modern air-to-water heat pump runs at 300–500% seasonal efficiency, and KRONOTERM models reach above 800% (ETERA water-to-water, SCOP 8.48). That is the efficiency gap: a heat pump delivers 4 to 8 times more heat per unit of primary energy than the best gas boiler.
The efficiency gap is even larger than against gas. Oil boilers typically achieve 80–85% efficiency, while modern heat pumps deliver 350–850% seasonal efficiency. For the same heat output, a heat pump uses 4 to 10 times less primary energy than oil heating. Switching from oil to a high-efficiency heat pump like KRONOTERM ADAPT (SCOP 6.22) typically cuts heating costs by 60–75%.
Yes — significantly. Compared to a gas boiler at 90% efficiency, a KRONOTERM heat pump at SCOP 4.5 uses 4–5 times less primary energy per unit of heat. Compared to oil heating, the gap is even larger. Real savings depend on insulation, flow temperature and electricity tariff, but typical UK and Irish homes switching from oil see 60–75% lower running costs.
When comparing heat pumps, check the SCOP under EN 14825 for your climate zone (UK and Ireland fall closest to “Average”), the operating temperature range (KRONOTERM ADAPT works down to -25 °C), the sound pressure level (16 dB at 5 m is exceptional), and the refrigerant type — natural R290 is future-proof against EU F-gas rules. A SCOP above 5.0 indicates premium efficiency.
Heat pumps work very well in winter — they continue heating efficiently even below -25 °C outdoors. Even on the coldest days, a high-efficiency unit still delivers two to three times more heat than the electricity it uses. In the typical UK and Irish winter band of 5–10 °C, efficiency rises to 4–5 times — far above any boiler.
No — underfloor heating helps but isn’t required. The key is the design flow temperature, not the emitter type. Underfloor heating allows the heat pump to run at low flow temperatures (35–40 °C) where efficiency peaks. Upsized radiators do the same job in retrofits. Every 1 °C lower flow temperature raises seasonal efficiency by 2–3%.
Yes. All KRONOTERM heat pumps carry the EHPA HP Keymark – the European quality label awarded by the European Heat Pump Association based on independent third-party testing under EN 14511 and EN 14825. ADAPT, ETERA and VERSI are tested under TUV protocols, ensuring published SCOP figures (6.22, 8.48, 5.95, 4.97 respectively) match field performance.
