Is it cheaper to run the heating continuously 24/7?
The Headlines
It is best to assume that this will USUALLY be more expensive and it can be a LOT more expensive.
There are exceptions though that I will cover later.
The universal advice of independent experts for most homes the cheapest thing is:
DON'T leave it on 24/7
only using the heating when you need the home warm is usually the cheapest option, such as using it on a timer
Key note of caution: Every home and situation is different, and can be VERY different. You will see comments on social media by people saying they believe 24/7 is 'best for them'. I urge caution here: They are talking about THEIR homes - you have no idea what sort of home, heating system or lifestyle they have. You can also not be certain that it is actually the cheapest option for them - it might just be that it suits them and they can afford it.
Quick links to sections below
So why is using a timer generally better?
The exceptions - when it MIGHT make sense to run 24/7
The secret to why some homes are actually suitable for 24/7
How to decide if it is right for you?
Summary
So why is using a timer generally better?
All homes leak heat in cold weather. Well insulated ones will as well, but less. External walls always feel cold to touch because they are taking heat out of your hand like a heat sponge.
The amount of heat homes leak is DIRECTLY linked to how warm it is inside, compared to how warm it is outside.
This means:
The warmer a home is, the more heat it will leak.
The longer a home is warm inside means it will have more time to leak heat.
If you have heating on in the morning and evening the interior of the house will be a little cooler in the middle of the day and overnight. During these cooler hours the home will leak less heat than the periods when the heating is on.
If you leave the heating on 24/7 it will be 'stood warm all the time' leaking heat.
Your radiators will then have to work harder to keep the place at the temperature you want and you will use more energy. It can be a LOT more!
Perhaps if you think of a home as a leaky bucket.
If you want to keep a leaky bucket full of water it will leak water out faster and you'll need to keep adding water to keep it full.
If you want to keep a home warmer for longer it will leak more heat and you'll need to keep adding heat from your heating system to keep it warm.
The exceptions - when it MIGHT make sense to run 24/7
There are SOME situations where running the heating 24/7 will make sense. This will only be if you have a modern condensing boiler and a range of other factors.
Whether your home is suitable depends on many factors including:
How much time you want to invest yourself getting to understand and manage your heating system to achieve efficient 24/7 heating
The house construction, thermal mass, insulation and draughts. Well insulated homes, draught proof homes are much more suited to 24/7 heating use for example.
How the house is used. If you are out most of the day and only need the home warm in the mornings and evenings, it is less likely that 24/7 operation is best for you.
How advanced the boiler is and whether the specific one you have is well suited to 24/7 operation for your home and how it is used.
How advanced the heating and boiler controls are. For 24/7 to be better it is particularly important to use slightly lower house thermostat temperatures at night or extended daytime periods when you are out of the home. A thermostat that can do this automatically is a really efficient way to do this. Different temperatures at different times can be set manually of course, but then you have to manage it several times each day.
Where the central thermostat is, whether it is fixed or wireless, what type it is, and what sources of heat or draughts are near it.
How the heating system is designed. Examples are whether the boiler is correctly sized (many are OVER-sized in the UK), or whether your radiators are large enough.
If the system is setup properly with the lowest possible radiator flow temperatures for 24/7 efficiency. If you don't have a combi boiler for example your ability to do this could well be reduced without some physical changes to your system.
Understanding these eight factors and how they relate to your circumstances is essential before committing to 24/7 use long term.
The secret to why some homes are actually suitable for 24/7
As I stated in the article above, 24/7 operation will inevitably result in a home leaking more heat. To keep up, the heating system will need to provide more heat. This will always be true no matter what.
BUT, if many of the eight factors are 'right' for your home, then boiler efficiency CAN be a lot higher than if the system just blasts heat into the house twice a day. In other words, it use less gas to run the boiler very efficiently for a long period, than very inefficiently for short periods.
SO, in suitable homes although more HEAT is needed, 24/7 operation will use less gas overall and so be cheaper.
How to decide if it is right for you?
Working out if your home is suitable is complicated as every home and set of circumstances is different. Here are a couple of ways you can do this though:
1) Try the Heat Geek network
Heat Geek is a unique organisation and network of highly trained and accredited heating engineers with a geeky edge for this sort of stuff.
They are experts in the art of the possible and may be able to help you directly. If you want to know more about what they say on this, I recommend watching this Heat Geek video.
They have LOADS of other web and YouTube content. It can be very technical though.
2) Try an experiment yourself
I'd strongly urge anyone thinking of switching to 24/7 heating to do this.
You could experiment by running your heating over a two-week period. Run the heating using the typical 'twice a day' timer settings you would normally use for one week, and then run the heating for a week on 24/7 using.
To make the experiment accurate and give you the best chances of success:
The weather over the two different weeks needs to be as similar as possible. It's not just outside temperature that needs to be similar both weeks - even wind, rain, and direct sunshine make a difference. Warmer weather in either of the weeks will reduce how hard the heating will have to work and mean you will get a big error in your results. Perhaps record average daytime and night-time temperatures during the two-week period.
Use slightly lower thermostat temperatures at night or during extended daytime periods. Some guidance on this here on the Heat Geek site.
Use the lowest boiler radiator flow temperatures that you can with your system. If your boiler is set at 75C flow temperature 24/7 operation will use considerably more gas. See here for information about boiler flow temperatures.
Thermostat settings (including radiator settings) should be the same for both weeks for the periods when you want to be warm.
Take accurate meter readings at the start and end of each week.
Doing a test over a shorter period than this (say just two consecutive days) will not give a proper comparison. The temperatures in the house need time to adjust from one heating arrangement to another - a quick test will give very a very inaccurate result.
Summary
If you are unsure, it is probably best to stick with the general expert advice - only put the heating on when you want your home warm.
Don't be influenced by the experiences of other people. Their situations could be dramatically differently to yours.
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Thanks.
Mark Thompson
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