The rapid growth of heat pumps is changing the way installers approach domestic hot water systems, but one thing hasn’t changed: the need to comply with G3 Building Regulations when installing unvented cylinders.
Recently members of the Hot Water Association (HWA) and installers took part in a panel discussion at InstallerSHOW about G3 and whether it needs to be updated to reflect the changes in today’s heating and hot water technologies.
To help address increasing questions from the industry, the HWA, working with the HPA UK, has published Unvented Hot Water Systems: Regulatory Compliance Explained. The guidance clarifies how existing regulations apply as low-temperature heating technologies become more common, while reinforcing that safety requirements remain unchanged regardless of heat source.
Historically, Approved Document G3 was written with high-temperature heat sources, such as gas boilers, in mind. However, today’s installations increasingly combine unvented cylinders with heat pumps, solar thermal systems and other renewable technologies, leading many installers to question whether the traditional safety controls still apply.
According to Stuart Elsy, Chair of the HWA, the answer is straightforward. “Whether the primary heat source is a boiler, heat pump, solar thermal or solid fuel appliance, the regulatory requirements remain the same. Safety must never be compromised as the industry transitions to low-carbon heating.”
Approved Document G3 requires any hot water storage vessel to incorporate measures that prevent stored water exceeding 100°C and ensure that any discharge from safety devices is conveyed safely without creating a risk to occupants. These legal requirements continue to underpin every compliant installation.
Alongside Building Regulations, installers must also comply with the Water Supply (Water Fittings) Regulations 1999. Schedule 2 specifies the safety devices required on unvented systems, including temperature controls, temperature and pressure relief valves, expansion control and correctly designed discharge arrangements.
The guidance also addresses one of the most common questions surrounding heat pump installations: can alternative control strategies be used?
While some manufacturers of integrated heat pump cylinder packages employ controls that differ from the arrangements described in Approved Document G3, these alternatives are only acceptable where they have been properly assessed and shown to provide an equivalent level of safety. In cases where installers wish to deviate from an approved product configuration, written agreement should be obtained from both the manufacturer and the relevant Building Control Body before installation proceeds.
The document emphasises that responsibility for compliance rests with the installer, designer or builder carrying out the work. Competence can be demonstrated through membership of a competent person scheme or by holding a recognised G3 qualification, while following manufacturers’ installation instructions remains essential.
As heating technologies continue to evolve, the HWA believes clear guidance is essential to avoid inconsistent interpretation of regulations. Rather than introducing new rules, the publication explains how existing legislation should be applied consistently across both conventional and renewable heating systems.
Stuart Elsy concludes: “The panel at installerSHOW unanimously agreed that building regulation G3 should be followed, but equally called upon government to review and update Part G to reflect renewable and low-temperature heat sources. The core of the present regulation is several decades old. HWA, The HPA UK and others are calling for regulation update to reflect current technologies.”
For installers working on the growing number of heat pump projects, understanding where innovation is permitted, and where regulatory requirements remain fixed, will be key to delivering safe, compliant installations and maintaining consumer confidence as the UK’s transition to low-carbon heating accelerates.
On the panel at InstallerSHOW were:
Eric Winter – Hot Water Association
Grant Gundelfinger, Director – DeltaTherm Ltd
Alan Clarke – Hot Water Association
Stuart Elsy, Chair – Hot Water Association
