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Person turning down heating flow temperature on boiler

Do you have a combi boiler? Reduce your energy usage with this simple boiler tweak.

By Jake Forrest | Posted September 30, 2022

By making a little change to your combi boiler, you can reduce your gas usage by up to 9% to save money while keeping your home just as warm.(1)

1. What is flow temperature and how can I reduce my energy usage?

Your heating flow temperature handles the temperature that your boiler heats water up to, before sending it off to your radiators. 

When your boiler is installed the flow temperature is usually set to around 70°C-80°C. This is too high for most combi boilers to run at maximum efficiency.(2)

At lower flow temperatures the combi boiler is in condensing mode more often. This means the combi boiler can capture more heat and recycle it back into the system. 

  • Lower flow temperatures result in a more efficient combi boiler. One that uses less gas to heat your home up to the same temperature. Therefore saving money and reducing your carbon footprint.

2. How much can I save by reducing the heating flow temperature on my combi boiler?

New research from the Salford Energy House found that lowering your heating flow temperature resulted in gas usage savings of:

  • up to 9% by lowering the temperature from 80°C to 60°C
  • up to 12% by lowering the temperature from 80°C to 55°C 

People who may be more vulnerable to the cold should be careful when reducing the flow temperature. For example, if you're elderly or have underlying health conditions. Innovation charity Nesta recommends not turning it below 60°C to ensure homes are properly heated.

A 9% reduction in gas usage would still mean an annual saving of up to £112 for the typical household.(3)

All without turning down the thermostat. 

3. Do I have the right type of boiler to reduce my flow temperature?

To change your heating flow temperature safely yourself, you must have a condensing combi boiler.

A combi (or combination) boiler sends hot water on demand to your radiators and hot water taps. The water isn't stored in a cylinder or storage tank.

You can find out more about the different types of boilers, with our boiler guide. You'll need to ensure you have the right type of boiler. 

  • If you have a system boiler or a hot water cylinder, please don't change your flow temperature on your own. It's important a qualified professional checks to see if your system is appropriate and safe. 

4. I have a hot water cylinder, why should I not change the flow temperature?

If you have a water cylinder, changing the flow temperature may not be right for your system. 

The water stored in the cylinder needs to be kept at 60°C or higher. This is to reduce the risk of harmful legionella bacteria growing(4). Bacteria can grow in the cylinder if the flow temperature is set too low. 

The temperature around your heating system can vary and drop. Don't change the flow temperature on your own without a qualified professional confirming it's right for your system.

  • This isn't a risk within heating systems that don't have water cylinders, as hot water is not stored in a separate tank.

5. What flow temperature is best?

The lower you set your flow temperature the longer it will take to heat your home.

It may take some trial and error to find the sweet spot for your home. Innovation charity Nesta suggests a flow temperature of 60°C, or slightly lower if your home is particularly well insulated. 

If you or anyone in your household is more vulnerable to the cold (for example the elderly or those with underlying health conditions) please don't set your flow temperature below 60°C. This should ensure your home heats up within a suitable time when your radiators initially come on.

The best flow temperature for your home depends on a few things. How well insulated your home is, its size and how quickly you want to heat your home. It's about finding the best balance for you between saving energy and heating your home quickly. 

6. How do I set the flow temperature on my combi boiler?

You control the flow temperature directly on your boiler. It doesn't take long at all and can be changed back at any time.

Money Saving Boiler Challenge is a campaign launched by the innovation charity, Nesta. To help people set their flow temperature they have an interactive online tool that offers help, depending on your combi boiler display type. 

If you're unsure, your combi boiler's user manual, which can be found on FreeBoilerManuals, will have extra guidance. If you're still unsure seek help from a qualified and competent professional. 

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7. Will this change how warm my home is?

Changing the flow temperature to the Nesta recommended temperature of 60℃, shouldn't change the temperature of your home.(5)

However, by reducing the temperature of the water being delivered to your radiators:

  1. Your radiators will feel slightly cooler to the touch.
  2. It will take slightly longer to heat your home when the radiators initially come on.

Only when you set the flow temperature too low will your heating system struggle to get your home temperature up to the level on your thermostat.

In the Boiler Flow Temperature Report heat-up times went from 23 minutes to 37 minutes after reducing the flow temperature from 80℃ to 60℃. Therefore, it took an extra 14 minutes to get the home up to the thermostat temperature of 21℃ when the radiators initially came on.

The heat-up time took an extra 33 minutes after reducing the flow temperature from 80℃ to 55℃. The exact heat-up times will depend on your home and thermostat temperature. 

8. Should everyone reduce their flow temperature?

We know how important keeping your home warm is.

Lowering the flow temperature on your combi boiler can be a great way to reduce your energy usage without turning down the thermostat.

However, reducing the flow temperature may not be appropriate for everyone. If you're worried about heating your home quickly it may not be right for you. If you're more vulnerable to the cold having a higher flow temperature can help to get your home up to the correct temperature more quickly.

And don't worry there are plenty of other ways you make your home energy efficient this winter.

9. What else can I do to save energy and lower my bills?

To help, we can give you a smart meter and access to our Free Energy Hub. This will help you understand how much energy you use and give you personalised energy-saving tips and advice.

You may be able to save up to £1,280 a year on your energy bills with cavity wall and loft insulation(6). Through EDF's website, you have the opportunity to buy professionally installed loft and cavity wall insulation. Get insulated and save.

You can also read our tips on energy saving at home. Some of these are easy to do and completely free.