A direct fired hot water system is fed via a direct fired water heater where the heat source for the water is physically located within the unit. This heater, such as an integral gas or oil burner, heats the water directly.

Direct fired hot water systems that use a direct fired water heater with a burner have an integral gas or oil burner that directly heats the water in the storage cylinder. They work by supplying hot gases through one – or more – exchanger fire tubes that sit within the cylinder. These tubes then transfer their heat to the surrounding water. These water heaters can be located separately from the main heating boiler but will require their own flue and/or gas connection and can take up more space.


Direct fired water heaters are solely dedicated to the provision of hot water generation, providing a faster heat up and response time than you get with an indirect system which is essentially ‘heating water to heat water’.


Where both high demand and fast recovery are required, the best option is a direct fired water heater, and adding additional storage vessels (buffers) can help as a backup (although longer recovery times needs to be considered).