# Heat Pump Calculator

> Calculate heat pump size, running costs, annual savings, and payback period for your home. Free instant results with cost breakdown.

Canonical: https://renoquant.com/heat-pump-calculator
Prices updated: 2026-03

## At a glance

A well-insulated 100 m² European home needs a 5–7 kW heat pump; a poorly insulated equivalent needs 15–20 kW, so insulation upgrades pay back twice over. Modern air-source heat pumps work down to −15 to −20 °C (COP drops from ~3.0 at 7 °C to ~2.0 at −7 °C) but still deliver more heat than the electricity they consume. Air-source installs take 3–5 days and typically cost EUR 8,000–15,000 in Europe; ground-source runs 1–2 weeks and EUR 15,000–25,000 because of borehole or trench work. Radiators may need upsizing to run at the heat pump's lower 35–55 °C flow temperatures.

## How to Size a Heat Pump

Correct sizing is critical for heat pump performance. An undersized heat pump cannot heat your home on cold days. An oversized heat pump short-cycles, reducing efficiency and lifespan. This guide explains the sizing formula and provides reference tables for common home types.

### The Heat Pump Sizing Formula

**Heat pump size (kW) = (Home area x Heat loss factor) / 1000 x 1.2 safety margin**

The heat loss factor depends on your home's insulation, age, and construction type. The 1.2 safety margin ensures the heat pump can meet demand on the coldest days without relying on backup electric heating.

### Sizing by Home Type

| Home Type | Area (sqm) | Insulation | Heat Loss (W/sqm) | Heat Pump Size (kW) |
|-----------|-----------|------------|-------------------|-------------------|
| Modern flat (2020+) | 65 | Excellent | 40 | 3.1 |
| 1990s semi-detached | 85 | Good | 70 | 7.1 |
| 1970s detached | 120 | Average | 100 | 14.4 |
| Victorian terraced | 90 | Below average | 140 | 15.1 |
| Period farmhouse | 200 | Poor | 180 | 43.2 |

Homes with poor insulation need very large (and expensive) heat pumps. Improving [insulation](/insulation-calculator) before installing a heat pump is almost always the better investment. Reducing heat loss from 140 W/sqm to 80 W/sqm can halve the required heat pump size and save thousands on the installation.

### Running Cost Comparison

| Fuel Type | Cost/kWh | System Efficiency | Effective Cost/kWh Heat |
|-----------|----------|-------------------|------------------------|
| Gas boiler (condensing) | EUR 0.065 | 90% | EUR 0.072 |
| Gas boiler (old) | EUR 0.065 | 75% | EUR 0.087 |
| Oil boiler | EUR 0.085 | 85% | EUR 0.100 |
| Electric heaters | EUR 0.245 | 100% | EUR 0.245 |
| LPG boiler | EUR 0.120 | 85% | EUR 0.141 |
| Heat pump (SCOP 2.8) | EUR 0.245 | 280% | EUR 0.088 |
| Heat pump (SCOP 3.5) | EUR 0.245 | 350% | EUR 0.070 |

A heat pump with a SCOP of 2.8 (a conservative estimate for air source) has a running cost similar to a modern gas boiler. With underfloor heating (which allows higher flow temperatures), SCOP can reach 3.5+, making the heat pump significantly cheaper to run. Pairing a heat pump with [solar panels](/solar-panel-calculator) can further reduce running costs by generating free electricity during the day.

### Annual Heating Cost by Home Size

| Home Size | Heating Demand | Gas Boiler | Oil Boiler | Heat Pump (2.8) | Heat Pump + Solar |
|-----------|---------------|------------|------------|-----------------|-------------------|
| 60 sqm | 8,400 kWh | EUR 605 | EUR 840 | EUR 735 | EUR 515 |
| 100 sqm | 14,000 kWh | EUR 1,010 | EUR 1,400 | EUR 1,225 | EUR 858 |
| 150 sqm | 21,000 kWh | EUR 1,515 | EUR 2,100 | EUR 1,838 | EUR 1,287 |
| 200 sqm | 28,000 kWh | EUR 2,020 | EUR 2,800 | EUR 2,450 | EUR 1,715 |

*Based on 70 W/sqm heat loss, 2000 heating hours/year. Heat pump + solar assumes 30% of electricity from solar panels.*

The biggest savings come from replacing oil or LPG heating. Replacing a modern gas boiler with a heat pump saves less on running costs but significantly reduces CO2 emissions and future-proofs against gas price rises.

## Frequently Asked Questions

### What size heat pump do I need for my house?

Heat pump size depends on your home's heat loss, which is determined by size and insulation quality. A well-insulated 100 sqm home needs approximately 5-7 kW, while a poorly insulated home of the same size may need 15-20 kW. Our calculator factors in both area and insulation quality to give an accurate sizing.

### Are heat pumps cheaper to run than gas boilers?

It depends on fuel prices. Heat pumps are 2.5-3.5 times more efficient than gas boilers, but electricity costs 3-4 times more than gas per kWh. At current European prices, running costs are roughly similar, but heat pumps win on CO2 and future-proofing as gas prices rise and the grid gets greener.

### How long does a heat pump installation take?

A typical air source heat pump installation takes 3-5 days. This includes mounting the outdoor unit, running refrigerant and electrical connections, modifying or replacing the existing heating circuit, and commissioning the system. Ground source installations take 1-2 weeks due to borehole or trench work.

### Do heat pumps work in cold climates?

Modern air source heat pumps work efficiently down to -15 to -20 degrees Celsius. Performance drops in extreme cold (COP falls from 3.0 at 7C to around 2.0 at -7C), but they still produce more heat than the electricity they consume. In Scandinavia, heat pumps are the most popular heating system.

### Can a heat pump replace my gas boiler directly?

Yes, but some modifications may be needed. Heat pumps produce water at 35-55C compared to a boiler's 60-80C. If you have radiators, they may need upsizing or you may need to add a few more. Underfloor heating works perfectly with heat pumps at their most efficient temperatures.

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Interactive version with calculator: https://renoquant.com/heat-pump-calculator. Figures are estimates; final quotes vary by site conditions, materials, and region.