Greg Brushett, Sales Director, Adveco, provides some thoughts on Commercial Gas Water Heating.
The UK commercial building stock is entering a complex transition. Driven by legally binding Net Zero targets for 2050, the policy trajectory moves decisively toward electrification. However, natural gas remains the dominant commercial energy source for domestic hot water (DHW). Data from the Department for Energy Security and Net Zero (DESNZ) shows that of the 1.8 to 2million non-domestic UK buildings, 65% to 70% rely on the gas grid.
The alternative of transitioning fully to an air source heat pump (ASHP) carries significant capital hurdles which are unlikely to markedly change, meaning procurement and installation will continue to typically cost three and a half times more than high-efficiency gas alternatives.
Older commercial premises also frequently lack the electrical headroom for large heat pump arrays. Upgrading grid infrastructure via a distribution network operator (DNO) can add £20,000 to £250,000+ to project costs, frequently stalling plans.
Operationally, UK commercial energy tariffs average 7p per kWh for gas versus 27p per kWh for electricity. Although heat pumps achieve high operational efficiencies (300%+), generating high-temperature commercial flow rates degrades this efficiency, pushing operating costs three to four times higher than gas without massive thermal storage investments.
Environmentally, modern condensing gas water heaters operating at 91%+ efficiency represent a substantial upgrade. Upgrading an obsolete non-condensing unit delivers a 35% drop in gas consumption, yielding up to £220,000 in lifetime fuel savings. Modern units are also future proofed for the potential introduction of up to a 20% hydrogen blend in regional or national gas networks for future carbon reduction. An optional hybrid strategy with ASHP or particularly solar thermal for base-load pre-heating and high-efficiency gas for peak topping and mandatory ACOP L8 legionella pasteurisation cycles (storing water at 60°C), cuts carbon at manageable costs.
For facilities with intense peak hot water demands – schools, restaurants, leisure and healthcare facilities – gas systems provide a power density that electric alternatives still struggle to match economically. The government’s Heat and Buildings Strategy avoids forcing premature scrappage of working machinery, focusing instead on natural trigger points at end-of-life.
Even with a 2035 phase-out ambition for new gas boiler installations, upgrading to high-efficiency gas water heaters provides 15-plus years of reliable operation, forming a practical bridge to new energy systems by 2050. So, sticking with gas during a replacement cycle remains a highly pragmatic economic and environmental choice for commercial operators.
Evolving DHW Installation
This is good news for gas-accredited installers, with a further decade of commercial installation projects in the offing alongside ongoing service and repair well into the 2040s and beyond.
But it is worth remembering that executing a gas-to-gas upgrade requires moving past simple like-for-like assumptions. Approved Document L (Volume 2) mandates a minimum seasonal efficiency of 91% (Gross Calorific Value) for replacement commercial water heaters, ending the non-condensing era. Installers must navigate four physical and mechanical constraints: sizing, access, fitting, and flueing.
Sizing
Oversizing causes capital waste and standing thermal losses, while undersizing creates operational failure. For a successful installation, the design must establish the building’s true demand profile: hot water volume, peak hourly usage, and required delivery temperatures.
Specifications should ideally leverage historical data from sub-meters, which are required on 90% of energy use in buildings over 1,000 m². If data is lacking, temporary metering can be instigated, and expert DHW engineers, such as those at Adveco, can aid in calculating peak profiles using occupancy patterns and fixture counts.
Access
Replacing large, commercial water heaters is a heavy, physical task. Standard 300- to 380-litre commercial units will still weigh 250-300 kg empty and 550-700 kg when filled. Installers need to consider a structural route survey before delivery.
Commercial plant rooms are frequently buried in basements or confined to rooftops, requiring transit via service lifts or tight structural openings. Verifying door widths and lift capacities against the appliance’s footprint eliminates costly installation-day delays.
Fitting
Retrofit installations also require the new appliance to adapt to existing pipework runs rather than the reverse. Specifying units with multiple connection options significantly reduces the time and expense of rerouting pipework in crowded plant rooms. Look for ‘universal retrofit’ options afforded by multiple connection points across top, front, side, and rear positions. This simplifies mapping connection position and height into site drawings to ensure physical compatibility.
Services must also be validated under load. Systems require stable inlet pressures between 17.0 and 25.0mbar for G20 natural gas. A supply line that drops below these limits during peak firing will cause commissioning failure. Single-phase 230V/50Hz/2A power demands are standard, but installers must ensure dedicated unvented kits and matching controls are procured as a unified package.
Flueing
Because condensing appliances extract latent heat, exhaust gases are far cooler than legacy systems. Old metal flues or masonry linings are incompatible and must be replaced with dedicated polypropylene (PP) or stainless steel systems. Installers must also run dedicated drainage for the acidic condensate produced. Flue upgrades and plant modifications can double baseline installation costs, meaning they must be budgeted upfront.
Installers should evaluate three main flue configurations against manufacturer length limits. Open Flue (B23) for long runs up to 41m (80mm) or 56m (100mm). Concentric Flue (C13/C33) for neat single penetrations up to 15m or 40m. Or Twin-Pipe Flue (C53/C63) for separating intake and exhaust paths around architectural barriers. All equations must factor in friction loss from elbows, which subtracts from the maximum linear run.
In conclusion
Upgrading an ageing commercial gas system to a high-efficiency condensing model is a legally compliant, cost-effective next step for UK businesses. By carefully calculating sizing, verifying access, maximising connection layout flexibility, and selecting correct flue configurations, installers can deliver immediate carbon reductions and substantial capital and operational savings. All while bridging the gap smoothly toward a net-zero future in line with the customer’s broader sustainability goals.
Image: Adveco
