A hybrid (or dual fuel) heating system combines a high efficiency continuous flow water heater or Hydrogen ready water heater with a renewable heating system such as a heat pump.

For projects looking to replace their domestic hot water system with a more energy efficient and greener solution, if there is a good level of building insulation a hybrid system would be an option. A hybrid provides designers and building operators with the familiarity of the continuous flow water heating system with the renewable energy of an air source heat pump. The Rinnai Hybrid solution is market leading in terms of energy conservation, as the Rinnai water heater will read the temperature of the preheated hot water and modulate the gas input to boost the water to the required temperature. This means that the renewable gains are maximised and the use of Natural gas or Hydrogen in the future is optimised.

Hybrid heating systems are the natural next step for the heating industry as the government strives to reduce our reliance on fossil fuels. The system includes both a water heater and a heat pump to deliver an efficient and cost-effective heating system all year round. The water heaters will make up for the performance of the heat pump when supplying high levels of hot water.


An air source or ground source heat pump extracts heat from the air outside and uses it to heat the building and produce hot water. For DHW the hybrid system will need to be accompanied by a storage vessel, this vessel is filled with preheated hot water that utilises the energy from the heat pump as the primary heat source. As the performance of the heat pump can change with the seasons and the hot water requirement for the building maybe beyond the capability of the heat pump alone, the incorporation of Rinnai continuous flow water heaters becomes necessary.

The Rinnai technology is equipped with smart controls that monitor the incoming water temperature and boost it accordingly, this ensures that the renewable heat generated is maximised and the only energy needed is to boost the temperature to the required set point by only using the required amount of energy. This can become critically important for ensuring temperature of anti-legionella regimes for applications that require hot water above 60 degrees constantly.

Heat pumps run on electricity, so they do have some impact on the environment, but the heat they extract from the ground or air is ‘free’ energy and is continually being renewed naturally. There are two types of heat pump which are commonly integrated into a hybrid heating and hot water system: ground source heat pumps and air source heat pumps (air-to-water). Usually, hybrid heating systems include an air source heat pump as these don’t require as much outside space and are simpler to install.

A ground source heat pump extracts heat from underground. Pipes are buried in the ground either horizontally in loops or vertically downwards. A fluid passes through these pipes which extracts heat from the ground and transfers it to a heat exchanger. This heat exchanger heats water for your taps and central heating.

An air source heat pump is a fan unit which is installed outside where it extracts heat from the air outside, even in temperatures as low -15°. This heat is used to heat water for your taps and central heating.