A 6-10kW boiler will comfortably heat the vast majority of UK homes on a very cold day. However gas boilers start at 11-13kW for heat only/ system boilers and 16-18kW (and higher) for combi boilers. It is clear that even the smallest boiler will heat the majority of UK homes, however that comes with a slight caveat for hot water production.
Combi boilers often appear ‘larger’ because they show outputs of 24kW and upwards, but this is for hot water production. For boilers that work with a hot water cylinder, hot water production is a factor for sizing, so you may need a larger boiler depending on your system set up. For more help try our Guide to boiler sizing.