Condensing boilers work at their most efficient when they condense, and this requires the return water temperature to the boiler to be around 50°C or less. However, we do not recommend changing radiators for larger versions to achieve this as it is uneconomical, and for most of the year the radiators will be oversized anyway. The Grant Vortex will operate efficiently on any system and even when not condensing, the larger heat exchange area will mean you will still be saving money against a standard boiler.