Save up to 8% on your Gas bill by turning down your boiler.

Households could save 6-8% in gas use just by turning down their boiler ‘flow’ temperature on their condensing boiler.*

The current cost of living crisis is significantly affecting household bills. Surprisingly, most modern condensing boilers have not been optimised for efficiency. Consequently, this increases gas use and carbon emissions. Your boiler will run more efficiently without compromising on comfort by simply reducing the boiler flow temperature of your condensing boiler.

*The Heating and Hot Water Council (HHIC)

What is my boiler ‘flow temperature’?

Boiler flow temperature is your boilers target temperature that your boiler heats water to send around your radiators. Gas boilers were traditionally set up with a flow temperature of 80°C. This means the boiler heats up the water to 80°C and that by the time the water is passed through the radiators, it returns to the boiler at around 60°C, having given off the remaining 20°C to the room.

However, modern condensing boilers should have a flow temperature set below 80°C. At temperatures this high the boiler is simply not condensing enough and will undeniably be inefficient.

Modern boilers have a variable efficiency between A-E. They are only A-rated when set up correctly. Studies have found most to be C-E-Rated in the home, equivalent to just 75-85% efficiency.

Your installer should have reduced the flow temperature to give the boiler a chance to run in ‘condensing mode’ as often as possible. It does this by recovering heat from the flue gas that was previously lost through the flue on old style boilers.

At a 70/50°C flow return temperature, the boiler will start to operate in condensing mode. Only when the flow temperature is 60°C or lower will the boiler recover enough heat to reach its higher efficiency potential.

boiler temperature

How do I turn down my boiler flow temperature?

This is generally adjusted via the controls on the front of your boiler. To be clear this is not your room thermostat. There are many variations from simple dials to digital displays, we suggest:

Referencing your boiler user manual for instructions on how to do this.

Call the boiler manufacturer’s technical helpline for customers.

Ask your installer or service and maintenance engineer.

How low should I set my condensing boiler temperature?

Some trial and error is required. Undoubtedly, factors such as the size of your radiators, the level of insulation, the outside temperature and the set room temperature will all affect how low you can reduce the boiler flow temperature. As a guide:

  • Most older homes can run their heating systems at 60-65°C 
  • Newer homes at 50-55°C. 
  • Peak efficiency may be at 45°C flow temperature, this can be too low for older properties.

Lower flow temperatures require a larger surface area of radiators or heat emitters to meet the desired room temperature. This is why underfloor heating or much larger radiators are required for an air source heat pump. If your existing system temperature can be reduced to 45°C then it could be heat pump ready.

Radiators are generally bigger than they need to be.  The industry often sized based on guesswork or used basic online calculators that almost always overcompensate. We recommend trying it at 60°C. If you have a home built after 2010, try 50°C.

Homes with modern double glazing, cavity walls and good levels of insulation should be able to drop boiler flow temperatures down without an impact on comfort. Even older homes, particularly terraced houses, will be able to do this if they have been modernised and draft proofed.

boiler temperature

Will I notice any difference?

Yes. Your radiators will feel cooler than they were previously. Providing your home does not feel cold and you do not feel cold, the boiler and system are working correctly and more efficiently.

Additionally, it may be necessary to run your heating for longer periods and allow more time for the house to warm up initially. Although it can seem counter productive to have the boiler on for a longer periods, you will generally be using less gas over a longer period at a lower temperature.

For those that have the heating on much of the day, you will almost certainly experience a smooth transition to lower temperatures.

If you have a health condition staying warm can be extremely important. In this instance, we would advise that you do not risk your well being by making adjustments to your heating system.

What if I have a hot water cylinder? 

Caution must be used if you are planning to reduce the flow temperature of your boiler and have a hot water cylinder. Stored hot water should be able to reach temperatures high enough to kill bacteria such as  legionella. The HSE recommend that water is stored at above 60°C. More information can be found Here