Retrofit upgrade to a 45 year old Government office building of over 5,400m2. The existing electric heating system was removed and replaced with high efficiency BAXI gas fired boilers which played a key part in reducing the buildings carbon footprint and achieving the target NABERS 4.5 star rating. BAXI PowerHT condensing boilers were selected for their high efficiency, compact size and the modular arrangement which made tham easy to install under restricted space conditions. The boilers have been in operation for two heating seasons and the maintenance contractors have provided positive feedback regarding their reliability and operation. The plant room contains 3 x 100kW Baxi PowerHT boilers in cascade controlled by a RVA47 Sequence Controller.