90.3 – 90.8% Gross SAP2009 annual efficiency 5 year guarantee when installed by a G1 accredited installer (T&C’s apply) Fitted with tried and trusted Riello RDB Lo-NOx burner Exceptionally quiet operation Unique Grant Vortex stainless steel heat exchanger Factory-fitted multi-directional flue Frost stat set to 5°C (factory fitted inside control panel)