Plant Room Rebuild — Oversized Boiler System Downsized for Efficiency

The existing plant room housed two Keston 55kW boilers — a combined output of 110kW that was significantly oversized for the property's actual heat demand. Oversized boilers are one of the most common and least diagnosed problems in London heating systems. When a boiler's output far exceeds the property's heat loss, it short-cycles: firing up at full power, satisfying the thermostat within minutes, and shutting down again before it ever reaches efficient condensing mode. The result is higher gas bills, uneven heating, increased wear on the heat exchanger, and a shorter boiler lifespan.

In this property, the problems were compounded by pipework that had been added and adapted over years without a coherent system design. The underfloor heating and hot water circuits were not independently zoned, meaning the system couldn't prioritise hot water or control the UFH separately. Heating was uneven across the property, hot water temperature was inconsistent, and gas consumption was higher than it should have been for a property of this size.

RARE's approach began with a proper heat loss calculation for the property — the essential first step that the original installation had clearly never benefited from. The calculation confirmed that the property's actual heat demand was well below 110kW, and that a combined output of 75kW (45kW + 30kW) would provide comfortable headroom while allowing each boiler to operate in efficient modulation range for far more of its running cycle.

The plant room was rebuilt from the ground up. Both old Keston 55kW boilers were removed. A new Keston Heat 45 (45kW) and Keston System S30 (30kW) were installed in a cascade configuration, with all pipework reconfigured to allow proper zoning of the underfloor heating and hot water circuits. Three Grundfos circulating pumps were installed to manage the primary, secondary and UFH circuits independently. The entire pipework network was re-lagged, cleaned up, and re-routed for logical system operation and future serviceability.

The system controls were reconfigured to allow independent operation of the UFH and hot water — meaning the property can now prioritise hot water recovery, control the underfloor heating to separate schedules, and run each boiler at the most efficient modulation level for the current demand rather than firing both at full power.