Estimate the correct heat pump size for your property
The Heat Pump Sizing Calculator helps you estimate the correct heat pump capacity for your property. Correct sizing is critical for heat pump performance—an undersized unit may struggle to heat your home, while an oversized system can short cycle, waste energy, and increase running costs.
This tool provides a practical starting point for selecting the right heat pump size based on your property’s heat demand.
Unlike traditional boilers, heat pumps work best when they run steadily at lower temperatures. Accurate sizing ensures:
Consistent indoor comfort
Lower electricity consumption
Longer system lifespan
Quieter operation
Better return on investment
Incorrect sizing is one of the most common causes of poor heat pump performance.
The calculator estimates your heating requirement using key building and system inputs.
You may be asked to enter:
Property size or heat loss value
Insulation level
Building type and age
Local climate conditions
Desired indoor temperature
The tool then calculates:
Estimated heat demand (kW)
Suggested heat pump capacity
Guidance on system suitability
Heat demand is the amount of heat required to maintain a comfortable indoor temperature during cold weather. It depends on:
Floor area and ceiling height
Insulation quality
Window and door performance
Air leakage
Outdoor design temperature
Small apartments: 4–6 kW
Average homes: 6–10 kW
Large or poorly insulated homes: 10–16+ kW
Actual requirements vary significantly depending on insulation and climate.
The Heat Pump Sizing Calculator is ideal for:
Homeowners considering heat pump installation
Landlords upgrading heating systems
Heat pump installers and designers
Energy assessors
Retrofit and renovation projects
✔ Quick and easy size estimation
✔ Helps avoid over- or undersizing
✔ Supports energy efficiency planning
✔ Ideal for early-stage design decisions
✔ Suitable for air-source and ground-source heat pumps
Leads to short cycling, higher costs, and reduced efficiency.
Results in poor comfort and increased reliance on backup heating.
Insulation improvements can significantly reduce required heat pump size.
No. It provides an estimate. A professional heat loss calculation is required for final system design.
Yes. The calculator applies to both types, although system design details may differ.
Oversizing reduces efficiency and comfort. Correct sizing is always recommended.
Yes. Radiators or underfloor heating must be able to deliver required heat at lower flow temperatures.
Absolutely. Better insulation reduces heat demand and allows for a smaller, more efficient system.
Upgrade insulation before installation
Use weather-compensated controls
Ensure emitters are correctly sized
Operate at lower flow temperatures
Maintain steady operation
This calculator provides estimated results only. Final heat pump selection and system design must be carried out by a qualified professional in accordance with local regulations and manufacturer guidelines.
The Heat Pump Sizing Calculator is a valuable first step in planning an efficient, reliable heat pump system. By understanding your property’s heat demand, you can make informed decisions, avoid common mistakes, and maximise the performance of low-carbon heating.
Use this tool as part of a broader approach to energy efficiency and sustainable heating.