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Heating & gas calculator

Heat pump calculator: running cost, SCOP, size & savings

Models an air-source heat pump month by month for your climate: heat demand, COP at every outdoor temperature and flow temperature, electricity use, running cost versus your current boiler and CO₂ saved.

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Results

With a seasonal COP of 3.39, the heat pump would cost about 1,180 €/yr to run, 445 € less than your current heating. It stays cheaper as long as electricity costs less than 3.9× your fuel price per kWh (now 2.8×).
Heat pump running cost
€1,180
4,214 kWh of electricity per year
Seasonal COP (SCOP)
3.39
heating + hot water, weather-compensated 45 °C flow
Current heating cost
€1,625
16,253 kWh of fuel at 88% efficiency
Annual saving
€445
Heat demand
14,303kWh/yr
102 kWh/m²·yr incl. hot water
Design heat loss
5.5kW
at -9 °C outdoor
Heat pump size
5.5kW
suggested nominal output
Backup heater share
0%
2 kWh from the immersion/backup heater
CO₂ saved per year
1.5t
1.47 t vs 2.97 t now
Break-even price ratio
3.86
electricity ÷ fuel price per kWh
Simple payback
31 yr 5 mo
Heating degree days
2,418K·d (base 15.5 °C)
Berlin, Germany
Monthly heat delivered vs electricity used
COP by outdoor temperature
Annual running cost

Month by month

MonthMean °CHeat (kWh)Electricity (kWh)COPCost (€)
Jan0.62,5088363234
Feb1.42,1527003.07196
Mar4.81,8525343.46150
Apr9.61,0742614.1273
May14.25121184.3333
Jun17.5263663.9918
Jul19.6210553.8215
Aug19.2217573.8316
Sep15.1414974.2727
Oct101,0502524.1671
Nov5.21,7314923.52138
Dec1.82,3207453.11209
  • Climate: Berlin, Germany (1991–2020 normals, approximate). Day-to-day temperature spread is modelled with ±3.5 K bins.
  • COP model: a fraction of the Carnot limit with 3 K condenser and 5 K evaporator approach, plus a defrost penalty around 0 °C. Field-measured SPFs typically come in 0.2–0.5 below lab ratings when systems are poorly commissioned.
  • Hot water is assumed at ~1.6 kWh per person per day, plus 1 kWh/day of cylinder loss.

How this heat pump calculator works

The running cost of a heat pump is simple arithmetic: heat demand ÷ seasonal COP × electricity price. The trouble is that both inputs are usually guessed. Most online tools plug in a manufacturer’s SCOP and a rule-of-thumb heat demand, and end up 30–50% off. This calculator builds both numbers from physics and your climate:

  1. Heat demand. Your house is described by a heat-loss coefficient H (watts per kelvin). It comes from floor area × an insulation-dependent figure (3.0 W/m²K for an uninsulated pre-war house, down to 0.25 W/m²K for a passive house), or it is back-calculated from the fuel you burn now and the local heating degree days.
  2. Climate. Each month’s mean temperature is spread into eleven temperature bins. The means come from 1991–2020 normals for 16 preset cities, or from NASA’s satellite climatology for any point on Earth. The bins capture cold snaps, and those matter because COP is lowest exactly when demand peaks.
  3. COP at every temperature. In each bin the flow temperature follows a weather-compensation curve. COP is computed as a fraction of the thermodynamic (Carnot) limit, with a defrost penalty between −7 °C and +7 °C, where frost forms on the outdoor coil.
  4. Capacity limit. If the heat pump’s temperature-derated output falls short of the load, an electric backup heater covers the gap at COP 1.
  5. Hot water is added at 1.6 kWh per person per day plus cylinder losses, heated to the storage temperature you set.

You get monthly electricity use, a realistic SCOP, the running cost, a comparison with your current fuel and the CO₂ difference.

The formula

Space heat per bin = H × (T_base − T_out) × hours COP(T_out) = η × T_cond / (T_cond − T_evap) T_cond = T_flow + 3 K, T_evap = T_out − 5 K (kelvin) T_flow(T_out) = 22 + (T_design,flow − 22) × (20 − T_out) / (20 − T_design) Electricity = Σ heat / COP + backup SCOP = Σ heat / Σ electricity Break-even price ratio = SCOP / η_boiler

η is the share of the Carnot COP a real machine reaches: 0.42 for basic or older units, 0.47 for current mid-range models and 0.52 for premium inverter units running on R290. At 7 °C outdoor and 35 °C flow the standard grade gives a COP of about 4.1. At −7 °C and 55 °C it drops to about 2.2, which matches published EN 14511 data sheets.

Worked example: 140 m² house in Berlin

Take the defaults: 140 m² of average insulation (1.5 W/m²K), Berlin climate, 45 °C design flow with weather compensation, a standard-grade heat pump and hot water for three people. The house needs about 14,300 kWh of heat a year (102 kWh/m² including hot water). Berlin has roughly 2,400 heating degree days to a 15.5 °C base.

The heat pump delivers that with about 4,210 kWh of electricity, a SCOP of 3.39. January’s COP sits around 3.0 and April’s goes above 4. Design heat loss is 5.5 kW at −9 °C, so a 5.5 kW unit covers practically all of the demand; the backup heater adds just 2 kWh a year.

At 0.28 €/kWh the heat pump costs ≈ 1,180 € a year to run. The existing gas boiler (88% seasonal efficiency) burns 16,250 kWh of gas at 0.10 €/kWh, about 1,625 €. So the heat pump saves roughly 445 € and 1.5 t of CO₂ a year (1.47 t on a 350 g/kWh grid against 2.97 t from gas). It stays cheaper while electricity costs less than 3.86 times the gas price; today’s ratio is 2.8. At an installed cost of 14,000 € with no grant, simple payback is about 31 years. Grants, heat-pump tariffs and dropping the gas connection make the real difference here.

How to read the results

  • SCOP is the number to watch. Each 0.5 increase cuts electricity use by roughly 13–15%.
  • Design heat loss is the power needed on the coldest typical day. Use it to check installer quotes: a 12 kW unit for a 5 kW house is oversized.
  • Backup heater share above 3–5% means the heat pump is too small for your climate, or the flow temperature is too high.
  • Break-even price ratio shows how safe the savings are. If your electricity/gas ratio sits well below it, price swings won’t wipe them out.
  • Month-by-month table shows where the money goes. Winter months usually make up 60–70% of the annual bill.

Typical values

Situation Flow temperature Realistic SCOP kWh electricity per 10,000 kWh heat
New build, underfloor 30–35 °C 3.8–4.5 2,200–2,600
Retrofit, oversized radiators 40–45 °C 3.2–3.8 2,600–3,100
Standard radiators 50–55 °C 2.7–3.2 3,100–3,700
High-temperature unit, small radiators 60–65 °C 2.2–2.7 3,700–4,500
Ground source, underfloor 35 °C 4.2–5.0 2,000–2,400

Tips to cut heat pump running costs

  • Lower the flow temperature. Turn on weather compensation and replace the two or three smallest radiators. It is usually the cheapest efficiency gain you can buy.
  • Insulate first. A loft or cavity upgrade cuts both the heat demand and the heat pump size you need. Test it with the insulation savings calculator.
  • Use a heat-pump or time-of-use tariff. Running the compressor and heating the cylinder in cheap hours can lower the effective price by 20–40%.
  • Add solar PV. Summer hot water and shoulder-season heating can run largely on your own solar panels.
  • Run it steadily. Heat pumps work best long and slow. Deep night setbacks force high flow temperatures in the morning.

Limitations

The calculator uses monthly climate data with a statistical temperature spread, not an hourly simulation, so very windy or humid sites may see more defrost losses. Insulation presets are averages; a real heat-loss survey can differ by ±25%. The COP model represents typical modern units and specific products vary, so check the EN 14825 data sheet of the model you’re offered. Internal gains are folded into the 15.5 °C base temperature, and solar gains through glazing aren’t modelled separately. For ground-source systems use the ground source heat pump calculator.

Method & assumptions

Space-heating demand = heat-loss coefficient H (W/K) × heating degree-hours below the base temperature. H comes from floor area × an insulation-dependent W/m²K figure, or is back-calculated from your current fuel use and the local degree days. Each month is split into eleven temperature bins (normal distribution, σ = 3.5 K) so cold snaps, when COP is lowest, get the right weight.

For every bin the flow temperature follows a weather-compensation curve (design flow at the design outdoor temperature, falling towards 25 °C in mild weather), and COP = η × Tcond / (Tcond − Tevap) with η = 0.42–0.52 of Carnot depending on quality. If heat demand exceeds the heat pump's temperature-derated capacity, the shortfall is met by a direct-electric backup heater. SCOP = total heat ÷ total electricity.

Frequently asked questions

How much does it cost to run a heat pump per year?
Divide your annual heat demand by the seasonal COP and multiply by your electricity price. A typical European house needing 12,000–15,000 kWh of heat with a SCOP of 3–3.5 uses 3,500–5,000 kWh of electricity, roughly 1,000–1,500 €/yr at 0.28 €/kWh. Well-insulated homes with underfloor heating can come in below 600 €/yr.
What is a good SCOP for an air-source heat pump?
Manufacturers quote SCOP 4–5 at 35 °C flow under EN 14825 test conditions. Field trials of real installations typically measure seasonal performance factors of 2.8–3.5. Anything above 3.5 is very good and usually needs low flow temperatures (35–45 °C) and weather compensation.
Is a heat pump cheaper to run than a gas boiler?
It depends on the ratio between electricity and gas prices. A heat pump with SCOP 3.2 replacing a 90% boiler breaks even when electricity costs about 3.5× the gas price per kWh. Below that ratio the heat pump wins, and the calculator shows your exact break-even ratio.
What size heat pump do I need?
Size it to the design heat loss of the house at the local design outdoor temperature. That is often 4–6 kW for a modern 120–150 m² home and 8–14 kW for an older uninsulated one. Oversizing adds cost and on/off cycling, so get a proper room-by-room heat-loss calculation (EN 12831 or MCS) before installation.
Does a heat pump work in very cold weather?
Yes. Modern air-source units keep producing heat down to −20 °C or −25 °C, but their COP falls, typically to 2–2.5 at −7 °C with 35–45 °C flow. Only a few days a year get that cold, so the seasonal average stays much higher. Scandinavia has the highest heat-pump uptake in Europe.
Why does flow temperature matter so much?
The compressor has to lift heat from the outdoor air up to the flow temperature. Every degree less lift raises efficiency by roughly 2–3%. Dropping from 55 °C to 45 °C typically improves SCOP by 10–15%, which is why bigger radiators or underfloor heating pay off.

Sources & references

  1. Commission Regulation (EU) No 813/2013 — ecodesign requirements for space heaters (seasonal efficiency per EN 14825)
  2. IEA — The Future of Heat Pumps (2022)
  3. UK DESNZ — Electrification of Heat Demonstration Project: final report
  4. NASA POWER — climatology API (monthly long-term temperatures)
  5. UK DESNZ — Greenhouse gas reporting: conversion factors 2024

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