BOILERS & HOT WATER
Retrofitting gas water heating – a national challenge
Bill Sinclair, technical director, Adveco discusses one of the great Net Zero challenges the UK faces – that of retrofitting HVAC systems across the built environment
A
ccording to the Department for Business, Energy, & Industry Strategy (BEIS), there were 1,755,000, recognised non-domestic buildings in England and Wales at the end of March 2024. Of these, just 14.6% were constructed after 1996, and considering the rates of new construction it is easy to see why the UK Green Building Council (UKGBC) estimates that 80% of existing buildings will still be in use in 2050. This means the large majority require some or considerable retrofit if sustainable operation is to be achieved. Most of these buildings will be gas-connected and
still use a gas water heater and despite the drive for decarbonisation, like-for-like gas replacement continues to be popular. Given we often see systems operating longer than 20 years and in the extreme more than 40, replacing them with anything new is advantageous for all involved. Burner, heat exchanger and flue gas management technology have all advanced to deliver greater efficiency and lower fuel consumption. Still, there remains a broad checklist of requirements to address if the new water heater is to be suitable for the building’s retrofit. First and foremost, consider the location. At a
macro scale, where does the building sit geologically? This sets initial parameters based on the water quality. Hard water areas are better served by indirect heating to reduce limescale, whereas soft water locales prone to corrosion, require more robust construction in stainless steel or an enhanced porcelain application would be recommended. At the very local scale, does the new unit fit through a standard door? Does it need to navigate steps, how heavy is it? Would two smaller units be more easily installed, meeting the same hot water demands and at a possibly lower cost compared to a single large unit? Beyond the actual water heater itself, how much pipework needs adapting or replacing? Are there isolation valves on the current heaters, do they hold or are they passing? And can you make the new pipework from the existing valve? Or do you have to cut back further than the valve? An appliance which provides multiple connection points offers the best means of replacing an old one with a new water heater without major alterations to pipework, reducing system downtime and pipework costs. Proximity to a drain to pipe away condensate and provide for drain-down maintenance is also important. On this basis, it would also be sensible
to consider a shorter unit. Although an appliance’s capacity may be reduced, efficiency gains can more than make up for the difference. The other important consideration, with direct
safety implications, is ensuring the flue is fit for purpose and correctly installed. Aluminium flue, for example, has an expected lifespan of around 15 years. If the old water heater is close to or older than this, it is imperative that the flue also be replaced. Old non-condensing negative draught flue is also not suitable for new condensing appliances, and it is important to remember that changes to regulations may make the original terminal location unsuitable. Always check flue connections and kits available for the replacement water heater to ensure it can meet or improve on the existing installation. Additionally look for advanced features such as
onboard energy and water use metering, remote connection such as Wi-Fi for app-based control and management, or connectivity to the building management system (BMS) for remote fault alarm and monitoring/control. Most modern gas appliances will also support a
20% hydrogen blend without modification, providing a bridge to future green gas alternatives available from the grid.
Above: Bill Sinclair, technical director, Adveco
If the intent is to increase the building’s sustainability prior to the mid-2030’s then the DHW system can be expanded by integration of a heat pump or solar thermal system acting as a pre-heat source. For true carbon reduction, we would propose installing a renewable pre-heat and then replacing gas for an electric boiler. With a variety of floor- and wall-mounted electric boilers available up to 100 kW, most typical commercial applications can be serviced in a more environmentally friendly way. Operational costs will be higher while grid electricity remains more expensive than gas, but installation is far simpler and cost-effective with no flueing necessary,
zero NOx and potentially more than 55% lower carbon emissions.
14 April 2025
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