ATAG One Boiler Installation — Belgravia

The owners of this six-storey Chester Square townhouse had an unusual but entirely reasonable specification for their new boiler: it had to be inaudible from the master bedroom.

The boiler cupboard sat on the ground floor, directly below the master suite on the first floor. The outgoing Ideal boiler — 12 years old and in need of replacement — had developed an intermittent low-frequency hum during heat demand that was clearly audible through the floor above. The client had measured it at 43dB at source. That's not extreme, but in a silent bedroom at 3am, it's enough to wake a light sleeper.

The brief was straightforward in its ambition and demanding in its technical specificity: replace the boiler with one that would be inaudible from the master bedroom. Not quieter — inaudible. And it needed to serve a five-zone system, including two zones of wet underfloor heating on the ground and lower ground floors.

RARE's specification was built around a single benchmark: published noise performance. Most boiler manufacturers quote noise figures in their marketing material that don't survive comparison with independently measured real-world data. RARE's engineers maintain their own reference data from installations across London's high-specification residential market, based on in-situ measurements rather than manufacturer claims.

The ATAG One 25 was the specification. ATAG is a Dutch manufacturer whose London residential presence has grown significantly in the last decade, largely on the strength of its noise performance. The One 25 is a modulating condensing boiler with a heat exchanger design that runs significantly quieter than most UK-market competitors at comparable outputs — particularly at low modulation rates, where most boilers are noisiest. It was the right specification for this property.

Installation was single-day. The old Ideal boiler was removed and the pipework adapted to the ATAG's connections. A Heatmiser NeoHub 2 replaced the original five-zone programmer — commissioning all five zones (three radiator zones on floors one through three, and two UFH zones on the ground and lower ground floors) through the same hub and app. The client was shown the app before the engineers left. An in-situ noise measurement in the master bedroom with the boiler running at full load: 28dB. Inaudible with the door closed.