Boiler Flow Temperature Testing

In 2022 Nesta commissioned some research to understand the effects of lowering the flow temperature of combi condensing boilers and how much energy can be saved.  Within these controlled tests they used Drayton Auto-balancing TRVs to ensure a fully balanced system as a start point.

The research was carried out at the University of Salford Energy House test facility and was conducted by setting the interlock thermostat to maintain 21 °C in the living room with the TRVs set to maintain 18 °C in all zones except the bathroom (22°C). Before testing, the thermostats and TRVs were adjusted to achieve setpoint temperatures at the centre of each room at a 70ºC flow temperature.

Key findings:

  • By lowering the boiler's flow temperature, space heating gas usage was reduced. For example, reducing it from 80°C to 60°C saved 12% of the gas used to heat the house.
  • It slowed heat-up rates and lowered internal air temperature. e.g. when lowering from 80 degrees to 60 degrees, heat up times in the morning went from 23 minutes to 37 minutes.
  • The reductions in gas use measured were found to be primarily because of enhanced boiler efficiencies instead of reductions in air temperature.


The testing carried out by NESTA clearly shows that reducing boiler flow temperature has a positive impact on the system efficiency. However, it also highlights the importance for a central heating system to be correctly balanced.

Balancing not only ensures that every room within the property gets sufficient heat, but it also keeps the boiler in condensing mode for longer and can achieve on average up to an 8.8% energy saving. The easiest and most effective way of ensuring your system is constantly balanced is to install the Draytons Auto-balancing TRVs  which can be set to regulate the flow into each radiator based on its output. 

To read more about this study visit the NESTA website.

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