The Temperature Your Boiler Should Be Set At To Save Energy
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Looking to know what temperature your boiler should be set at? I’ve got all the information you need to warm your home effectively, without wasting energy.
Looking for easy ways to save energy? If you have a condensing combi boiler (one that controls your heating and hot water, without the need for a separate water tank), then one really easy and effective tip is to look at what both the heating flow temperature and the hot water temperature on your boiler is set at. They could be set too high. This costs you money, uses excess fossil fuels, and might not be heating your home efficiently.
Here’s all you need to know.
How To Identify The Heating Flow & Water Temperature Controls
Before we get into adjusting temperatures, it’s first really important to get to grips with the controls on your boiler. This is because we don’t want to adjust the wrong settings – doing so can be dangerous.
So, to help you out, here’s a photo of the control panel of my Worcester Bosch Greenstar combi boiler. I’ve annotated it so that you can see what the heating flow temperature and water temperature control looks like:
The heating flow temperature control is usually indicated by a radiator icon. Meanwhile, the water temperature control is generally indicated by a tap icon. If your combi boiler doesn’t use the radiator and tap icons, and you’re in any doubt, then it’s best to consult the manual first before adjusting anything.
What Your Heating Flow Temperature Should Be Set At
The heating flow temperature is the temperature at which your combi boiler heats up the water for your radiators.
It’s likely that if you haven’t touched it since your boiler was installed then it’s set too high. This is because many boiler installers set the temperature to 80°C or the maximum level it can heat to. However, that is too high for a condensing gas boiler to run efficiently. At this temperature, your boiler won’t enter condensing mode, which isn’t very efficient or cost-effective.
For combi boilers, it’s recommended that you set the radiator output temperature on your boiler to 60°C in winter to heat your rooms effectively without overheating. This is an optimum temperature for your boiler to heat your home quickly and efficiently.
However, bear in mind that all homes are built and insulated differently, and have different-sized radiators. As such you may find that temperature is too cool or too warm for your home. You might have to experiment by seeing if your house is warm enough until you find the optimum temperature for you.
Bear in mind that a reduced boiler flow temperature will mean it will take longer for your radiators to heat up and your radiators won’t feel as hot to touch. But as long as both you and your home don’t feel cold, then your heating system is working more efficiently, and you will be saving money.
In autumn and spring, you can reduce this temperature further – to between 50°C and 55°C – to heat your home optimally. Note that this advice only applies if you have a condensing combi boiler. If you have an older heat-only boiler with a separate hot water cylinder, then never lower the temperature below 60 to 65°C.
What Water Temperature To Set On Your Boiler
Now that you’ve set your boiler flow temperature, I’d also recommend checking the water temperature on your combi boiler.
You can even just have a think about how hot your hot water taps are. If you find you have to add a lot of cold water when you’re showering your hands to bring it to a comfortable level, then your boiler temperature is probably set too high.
This is because the average boiler hot water thermostat in the UK is set to 65ºC. This is very inefficient and could be using more energy and costing you more money than your bills should be.
At 65ºC, you have to cool the water that you’ve spent money heating with cold water to be able to use it in the bath or shower. It’s also quite an inefficient temperature, as heat loss from your boiler is also increased.
It’s recommended that you set your boiler temperature for water at 60ºC – but do not set it below 60ºC.
At 60ºC water is still sufficiently hot for almost all domestic uses. So go and turn the water temperature on your boiler down to 60ºC (but not before you’ve read the safety advice below).
It’ll take less than a minute to do and you’ll have a nice warm glow. Your boiler won’t have to work as hard, prolonging its life. You’ll also save both the environment and money. It’s estimated that you’ll save around £30 a year if you turn your boiler temperature down from 65ºC to 60ºC. This is a healthy amount to save for very little work.
An Important Word of Warning
Whilst you may want to set the water temperature as low as possible to save energy, it’s vitally important that you don’t set your boiler water temperature too low. This is because at low temperatures the bacteria responsible for Legionnaires’ Disease – a potentially fatal lung infection spread through the inhalation of waterborne particles – can thrive and multiply.
According to the Health & Safety Executive, the legionella bacteria (which cause the disease) do not survive at temperatures above 60°C. So never set it below 60°C – it’s not worth the risk.
What About The Room Temperature?
The optimum room temperature is around 18 to 21°C. This temperature range is the most comfortable and healthy for day-to-day living. Here are some tips on how to set the timer on your boiler if you need some advice.
The Bottom Line
So there you go: turning down the temperature on your boiler a few degrees will save you a pretty penny on your energy bills, and help the environment through reduced carbon emissions. And you’ll also reduce the risk of scalding from your bathroom or kitchen taps. This makes this tip a triple win!
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The physics is set q = m c deltaT where q = heat, m = mass c = specific heat capacity and delta T = temperature difference
The argument for the boiler running longer at a lower flow temperature can work for condensing combi boilers because they “recover” heat from flue gasses etc
In standard boiler situations it can be argued to run at higher flow temperatures because radiators will heat up quicker. Say in an oil boiler it is either running or not, so running it to a higher flow temperature to heat up the radiators quicker so it switches off, will be more efficient
These ‘standard boiler’ systems would normally be on an S-type system with separate valves to control flow to the central heating and hot water cylinder. The cylinder temperature is controlled by the cylinder thermostat which opens the valve, therefore a hotter flow temperature will heat the domestic hot water quicker. The cylinder has its own flow temperature thermostat so shouldn’t be confused by the boiler flow temperature
The temperature of the domestic hot water should be set at a safe temperature rather than one to save energy, so 60C – however – most articles on this mention the danger of legionella below 60. Legionella is an aerobic bacteria and therefore cannot survive in a closed heating system such as with a Megaflo type cylinder because there is no oxygen
Summary. Combi / condensing boilers lower the flow temperature. Standard systems raise it
If you have an oil boiler and “smart” controls such as radiator valves and thermostats, set water flow at 70-75C and program so that water and central heating come on at the same time in the morning so as to reduce boiler run time, ie, don’t heat your cylinder when the central heating is off
When turning down the boiler temperature, you need to consider the heat output generated by your radiators. Most radiators are based on delta 50 (70 degrees – 20 degrees) to calculate heat output. If you lower the boiler temperature to 60 degrees, your radiators will be operating at delta 40 (60 degrees – 20 degrees). Therefore, less heat is generated and more gas is used and the boiler is constantly burning and pumping. I tried setting my boiler to 60 degrees, ended up using more gas and the house never got past 18.5 degrees.
Unless you have oversized radiators that can pump heat at the same rate at a delta 50 rating when the boiler is at 60 degrees (delta 40) then there could be a saving. Due to my radiator sizing, it is not possible to run the boiler at 60 degrees as the boiler never stops. So my boiler is set to 74 degrees, this ensures the boiler will stop when the house reaches my thermostat set point of 20 degrees.
I understand where you are coming from. The only issue I would say is that if you have a condensing boiler, at 74 degrees it’s running at too high a temperature to actually condense. This means your boiler won’t run very efficiently. Turning it down a few degrees to 70 would allow your boiler to condense whilst still heating your home your preferred way.
While I agree that turning down the room thermostat or the thermostat on the hot water cylinder will save energy, I’m not sure I agree that turning down the boiler temperature will save anything, if thermostats remain at the same level. But first, there is a contradiction in what you say. You say that for combi-boilers turn down the radiator output temperature to 75. I do not have a combi boiler: the “same” water heats the hot water cylinder and the radiators – albeit with different circuits and thermostats – but the water temperature in the gas boiler is the same for both and cannot be individually adjusted. But irrespective of the type of boiler, if the thermostats remain the same, then it takes the same amount of energy to heat your house (or your water) to the given temperature. This means that if the boiler temperature is lower, it will take longer to heat your house (or water). With a longer time, the pump(s) will uses more energy, so in simple terms, assuming the same heat energy is required from the boiler, with the pump running longer you will use more energy. Also, will the longer time also result in greater heat losses from inefficiencies in the system (a longer time for heat losses to occur)?
I’m not sure it is as simple as ‘time to heat’ dictating total efficiency. Condensing boilers operate more efficiently if the return water temperature allows the condensing behaviour to happen, something like 50c is what I have read. Pumps and the like draw very little energy compared to the gas energy used, so optimising gas energy use is, I presume, the more important factor.
Shared heating between radiators and DHW require the flow temperature to be at or above the desired DHW temperature, which limits choice to 60c+ as to avoid Legionella DHW should be 60c according to Govt recommendations.
I would be interested in anyone chiming in here with the true facts of the efficiency argument.