Why Do You Need Heat Loss Calculations for Heat Pumps

The Importance of Heat Loss Calculations should not be overlooked when installing heat pumps as they ensure the effectiveness and proper sizing of a heat pump system. Accurate heat loss calculations determine the amount of heat lost from a building and the heating required to maintain a comfortable temperature.

Why is Heat Loss Calculation Important?

Traditional boilers operate with high-capacity outputs, delivering high-temperature heat to achieve desired room temperatures. While they may keep you warm, they are often not energy-efficient. On the other hand, heat pumps operate at lower capacity outputs, supplying lower-temperature heat to achieve the same room temperature. Therefore, precision in system design is critical for heat pumps.

An accurate heat loss calculation is essential when designing a low-temperature heating system like a heat pump. If the system is undersized, it won’t effectively heat the property, leaving homeowners feeling cold and uncomfortable. Oversizing, on the other hand, leads to energy waste, increased energy bills, and reduced system efficiency. Inaccurately sized heat pumps and radiator systems are the primary reasons behind stories of heat pump installations that don’t properly heat properties or are expensive to run.

Close up of a woman sitting near a radiator

A detailed room-by-room heat loss calculation provides an accurate assessment of the property’s total heat loss in watts (W). This data allows for the correct specification of the heat pump, as well as the required heating outputs for individual rooms. This precision enables the system to run at the lowest possible flow temperature, resulting in higher efficiency and lower running costs.

How is a Heat Loss Calculation Performed?

Heat loss calculations used for sizing heat pumps and achieving MCS compliance follow the calculation process outlined by the Chartered Institute of Building Services Engineers (CIBSE) and adhere to standards like the Domestic Heating Design Guide 2014 and EN 12831, as well as the UK standards for MCS MIS 3005.

A heat loss calculation considers several factors:

  1. External Temperature: Lower external temperatures lead to greater heat loss from the building. Local climate data for the property is therefor taken into account.
  1. Room Temperatures: Different rooms require different temperatures for comfort.
  1. Building Fabric: The construction of walls, floors, roofs, and windows, as well as the amount of insulation, all play a vital role in determining heat loss.
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New Build or Renovation Projects

To perform accurate heat loss calculations for new build or renovation projects, we will need access to the following.  Architectural plans, elevations, sections, SAP reports, U-values, building regulation construction details, and planned heating distribution details. We input these details into specialised software, which then calculates the heat loss for each room. This data enables the precise specification of the heat pump and distribution system.

Existing Properties

For existing properties considering a switch to heat pumps, we will need to visit the property to conduct our assessment. During the appointment, the assessor will measure all rooms, including window types and sizes. We also measure and note the type of existing radiators. All of the data we collect will be used to complete the room-by-room heat loss calculation.

Architect with new build plans
A picture of an Air Source Heat Pump


In summary, conducting a room-by-room heat loss calculation is critical to ensure an efficient and high-performing heat pump system. Accurately determining the required heating capacity helps maintain a comfortable temperature.  Homeowners can also avoid the pitfalls of either over sizing or under sizing their system.

Book Your Heat Loss Calculation

At Bluewire Hub Ltd, we offer MCS compliant room-by-room heat loss calculation services. Our prices start at just £195 for properties with up to 3 bedrooms.

Given that typical costs for an air source heat pump are around £14,000 (figures from the Energy Savings Trust), investing in a comprehensive, independent heat loss calculation is a wise decision. It will provide you with the essential information needed to make an informed choice regarding the suitability of a heat pump system for your property.

If you would like Bluewire Hub Ltd to perform a fully MCS-compliant room by room heat loss calculation for your project you can book our services here