How do calorifiers work and what are they?

A calorifier is an indirect-fired water heater to provide hot water in a heating and hot water system. Indirect fired means the water heater does not contain a burner. It is a storage water cylinder with one or more heat exchanger coils which contain hot liquids (water or solar fluid).

As an indirect fired water heater cannot produce the heat itself due to the missing burner, it relies on an external heat source such as e. g. a boiler or solar collectors. These heat up the liquid in the heat exchanger coil which in turn heat up the water contained in the vessel.

Learn more about the pros and cons of calorifiers and direct fired water heaters in our indirect vs direct hot water systems knowledge article.

When should I use a calorifier in a commercial heating system?

Indirect-fired water heaters still rely on another source to heat up its coils which means it cannot react as quickly to demand as a direct-fired water heater. In the past, it was necessary to have a dedicated hot water boiler to heat the calorifier. However, due to increased efficiencies, modern boilers can easily supply heat to a calorifier and the heating system.

This is useful in refurb projects. You can read about how our customer recently used the spare capacity from their existing boiler to provide the heat for a new calorifier to generate hot water for an office building. Read the case study here.

Want to know more?

We go into detail about direct- vs. indirect-fired water heaters on this page. Calorifiers are used generally where hot water demand is not exceptionally high and a slower heat up time is sufficient to satisfy the hot water requirements. They are more cost-effective than direct-fired water heaters and no flues are required,  but they can be more more prone to heat loss. However thanks to generous insulation this is minimised on all Hamworthy calorifiers.