As the UK increases its use of low-carbon heating, getting heat pump design right will become progressively important. The government’s Warm Homes Plan identifies heat pumps as the preferred form of electrified heating for the majority of homes and aims for the UK market to reach more than 450,000 annual heat pump installations by 2030.

But installing more heat pumps is only part of the challenge. To deliver the comfort, efficiency and performance people expect, systems need to be designed around the property they are heating. That starts with an accurate heat loss assessment.

What is a heat loss assessment?

A heat loss assessment determines how much heat a building needs to maintain comfortable internal temperatures during colder weather. It considers heat escaping through the building fabric, including walls, floors, roofs, windows and doors, as well as heat lost through ventilation and air leakage.

For domestic heating system design, calculations should be completed on a room-by-room basis, taking into account factors such as building fabric, room dimensions, air change rates, required internal temperatures and external design temperatures. This provides the information needed to determine both the overall heating requirement and the output required from heat emitters in individual rooms.

Elmhurst’s Heat Loss Calculator is designed to calculate heat loads in accordance with BS EN 12831-1:2017 and can produce calculations compliant with the MCS Heat Pump Standard, MIS 3005-D.

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Why accurate heat loss calculations matter

Heat pumps operate differently from traditional fossil-fuel boilers. Correct sizing is therefore fundamental to delivering an efficient system that provides appropriate levels of comfort throughout the property.

An accurate calculation helps the designer understand the peak heat requirement of the home and the requirement within each individual room. This then informs heat pump selection and emitter sizing.

Where a system is not designed closely enough around the building’s actual heat loss, performance can be compromised. Low-carbon heating systems such as heat pumps need to be closely matched to the specific requirements of the property, with room-by-room calculations supporting improved energy efficiency, running costs and occupant comfort.

The importance of heat pump design is recognised by government. Work undertaken through the government-backed Heat Pump Ready Programme has highlighted the potential for variation between property surveys and discrepancies between the way systems are specified and how they subsequently perform in practice. These issues can contribute to poor customer experiences and undermine confidence in the technology.

As heat pump deployment increases, consistency and competence in the design process will therefore become even more important.

A calculation is only as good as the information behind it

Although the methodology provides a structured approach, the accuracy of the final result depends heavily on the quality of the information entered.

In existing buildings, some characteristics cannot always be established with certainty during a visual inspection. For example, U-values may need to be derived from the age and construction of a building element, while air permeability may be based on standard assumptions where a measured result is unavailable.

A competent assessor must therefore understand the building, identify the evidence available and make appropriate judgements about the information being used.

Accurately measured evidence can also help strengthen the assessment. Elmhurst’s Heat Loss Calculator, for example, allows a measured air permeability result from an airtightness test to be entered instead of relying on the standard method. It can also use a measured whole-house Heat Transfer Coefficient to calibrate room and property heat loss calculations, although additional justification may be required where this is used for MCS compliance.

Better evidence can reduce reliance on assumptions and provide a more accurate understanding of how a building performs.

Building greater consistency into heat pump design

As demand for heat pumps grows, there is an opportunity to strengthen the connection between property assessment and heating system design.

Energy assessors, surveyors, installers and other building professionals can each bring valuable expertise to the process. For those carrying out heat loss assessments, however, appropriate training and competence are essential.

Elmhurst’s Heat Loss Assessor Training has been developed to provide professionals with the skills needed to undertake heat loss and heat load calculations in accordance with BS EN 12831. Successful learners can then join Elmhurst’s Heat Loss Assessor Competency Scheme, which provides professional recognition alongside access to technical support, specialist software and Elmhurst’s Search for an Assessor directory.

For installers, working with a trained Heat Loss Assessor can provide an additional source of building expertise at the beginning of the design process. For assessors, it represents an opportunity to apply existing surveying skills to an increasingly important area of low-carbon heating.

Most importantly, closer collaboration can help ensure that the information used to design a system accurately reflects the property.

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Getting the foundations right

Government support for heat pumps continues to expand. The Boiler Upgrade Scheme currently provides support towards eligible heat pump installations in England and Wales, while the government has set out its intention to continue growing the market significantly towards 2030.

At Elmhurst, we believe accurate and consistent heat loss assessment has an important role to play in achieving this. Heat pumps are proven technology, but good outcomes depend on getting the fundamentals right:

Understanding the building
Using appropriate evidence
Carrying out robust calculations
Ensuring the resulting information feeds effectively into system design

By strengthening competence and bringing assessors and installers closer together, the industry can help deliver better-designed systems and greater confidence for consumers.