Indirect Water Heater

An indirect water heater is a storage tank that is connected to an external hot water heater. Hot water from the external heater is circulated through a coil inside the tank to heat the water. They are different from your typical hot water tanks, which have an oil, gas, or electric heating element inside the tank.

These systems can also be called integrated or combination space and water heating systems.

The efficiency of an indirect water heater is incorporated into that of the entire combination or integrated space and water heating system. This is given as a combined appliance efficiency rating (CAE).

Indirect water heaters can be connected to high-efficiency water heaters such as ground source heat pumps or renewable energy sources such as solar water heaters.

Indirect water heaters that are connected to an oil or gas boiler can be less efficient than other types of direct water heaters because they depend on the central heating system to heat domestic hot water. A typical boiler is oversized for this application and will run at lower efficiencies because it will often have to go through a “cold start.”