The weather changes constantly.
A mild autumn afternoon can become a cold evening. Overnight temperatures can fall sharply. A bright winter morning can feel completely different from the grey day before it.
And every time the temperature outside changes, something happens to your home.
The amount of heat it loses changes too.
Yet most of us don’t want the temperature inside our homes to follow the weather outside.
We want the opposite.
We want the home to simply feel comfortable.
That is the idea behind weather compensation.
What is weather compensation?
Weather compensation is a heating control method that adjusts how a heating system operates according to the outdoor temperature. As it gets colder outside, the system can increase the temperature of the water flowing to the radiators or underfloor heating. As conditions become milder, it can reduce it.
The aim is to provide the heat the home needs without the homeowner constantly adjusting the heating.
In other words, the temperature outside changes what the heating system does so that, ideally, it doesn’t change how the home feels.
Why does the weather outside matter to your heating?
Every heated home loses heat.
Heat moves from the warmer environment inside the home towards the colder environment outside.
It is lost through different parts of the building, including walls, windows, floors and the roof, as well as through ventilation and air movement.
When it’s relatively mild outside, the difference between the indoor and outdoor temperatures is smaller.
When it becomes colder, that difference increases.
The home therefore needs its heating system to replace more heat in colder conditions if the indoor temperature is to remain comfortable.
This is the problem weather compensation is trying to solve.
Rather than delivering the same water temperature regardless of the weather, the heating system can respond to changing conditions.
How does weather compensation work?
The principle is relatively straightforward.
The heating system uses information about the outdoor temperature.
Its controls then use a heating curve, sometimes called a weather compensation curve, to determine an appropriate flow temperature for the heating system.
That process can be thought of simply:
Outside gets colder → heating flow temperature increases.
Outside gets warmer → heating flow temperature decreases.
The radiators or underfloor heating then receive water at a temperature intended to provide the amount of heat the home requires under those conditions.
And as the weather changes again, the system adjusts again.
The homeowner doesn’t need to continually predict what the weather is doing and compensate for it manually.
The heating system is designed to respond.
What is flow temperature?
To understand weather compensation, it helps to understand one other term: flow temperature.
Flow temperature is the temperature of the water leaving the heat source and travelling around the heating system towards the radiators or underfloor heating.
The hotter that water is, the more heat the emitters can generally deliver into the rooms.
But the home doesn’t require the same amount of heat every day.
Imagine a home that feels comfortable at 20°C.
If it is 14°C outside, relatively little additional heat may be needed to maintain that indoor temperature.
If it is 0°C outside, the same home will generally be losing considerably more heat.
The heating system therefore needs to respond differently.
Weather compensation does this by changing the flow temperature rather than simply waiting for the homeowner to become uncomfortable and turn the thermostat up.
What is a weather compensation curve?
A weather compensation curve, or heating curve, defines the relationship between the outdoor temperature and the flow temperature the heating system aims to provide.
You can imagine it as a line on a graph.
Along one axis is the outdoor temperature.
Along the other is the heating flow temperature.
As outdoor temperature falls, required flow temperature generally rises.
As outdoor temperature rises, required flow temperature generally falls.
For example, a system might require relatively low-temperature water on a mild day but a higher flow temperature during colder winter conditions.
The important point isn’t the exact temperatures in that example.
Those depend on the home and heating system.
The important point is that the required flow temperature isn’t necessarily fixed.
The system responds to what the home needs.
Why not just use the same flow temperature all winter?
Because the coldest day of winter isn’t every day of winter.
A heating system needs to be capable of keeping the home comfortable when outdoor temperatures become particularly low.
But if it operates at the same high flow temperature during much milder weather, it may be providing hotter water than the home actually needs.
Weather compensation allows the system to reduce the flow temperature when conditions allow.
That creates a more responsive relationship between the home, the weather and the heating system.
Rather than thinking:
This is the temperature my heating always operates at.
We can think:
What temperature does the heating need to operate at today?
Why is weather compensation particularly useful with heat pumps?
Weather compensation is particularly useful with heat pumps because heat pumps generally operate more efficiently when they can meet the home’s heating needs at lower flow temperatures. Weather compensation allows the flow temperature to reduce during milder conditions and increase as more heat is required.
This matters because heat pumps behave differently from the heating systems many homeowners are familiar with.
An air source heat pump extracts energy from the outside air and uses it to heat water for the home.
The temperature it needs to raise that water to has an important influence on the way the heat pump operates.
In general, a heat pump can work more efficiently when it can supply the home effectively using lower flow temperatures.
Weather compensation helps make that possible when conditions allow.
On a milder day, the home loses less heat.
So, assuming the heating system has been appropriately designed, the heat pump may be able to meet the home’s needs using a lower flow temperature.
As the weather becomes colder and the home loses more heat, the required flow temperature can increase.
Instead of operating as though every day were the coldest day of the year, the system responds to the conditions it is actually experiencing.
Does weather compensation mean your home gets colder when it’s warmer outside?
No.
This is one of the most important things to understand about weather compensation.
The flow temperature changes.
The desired indoor comfort doesn’t have to.
If the home needs less heat because conditions outside are mild, the system can deliver less.
If the home needs more because conditions outside are colder, it can deliver more.
The purpose of changing the heating water temperature is therefore to help maintain the conditions inside the home.
The weather changes.
The system responds.
The homeowner ideally notices neither.
Doesn’t the thermostat already do this?
A room thermostat and weather compensation perform related but different jobs.
A thermostat responds to the temperature it measures inside the home.
Weather compensation responds to conditions outside and adjusts the heating system accordingly.
That distinction can be useful.
Weather compensation gives the heating system information about a factor that is influencing the home’s heat loss: the temperature outside.
Rather than relying entirely on correction after conditions indoors have changed, the heating system can adjust its operation as external conditions change.
The exact way thermostats, sensors and weather compensation work together depends on the controls and system design.
But they shouldn’t be thought of as competing ideas.
They are different parts of controlling the same heating system.
Is every weather compensation curve the same?
No.
The heating curve needs to reflect the relationship between the outdoor conditions and the amount of heat that particular home needs.
That relationship begins with understanding the building.
What happens if the heating curve is set too high?
If the weather compensation curve is set higher than necessary, the system may produce hotter water than the home needs.
With a heat pump, unnecessarily high flow temperatures can reduce efficiency, which is why the aim is generally to use the lowest flow temperature that can still keep the home comfortable.
What happens if the heating curve is set too low?
If the flow temperature isn’t high enough for the heat loss of the home and the capacity of its radiators or underfloor heating, the system may struggle to maintain the desired indoor conditions.
Weather compensation works best when it is part of a properly designed heating system rather than treated as an isolated setting.
There isn’t a universal weather compensation setting that every homeowner should copy.
Do radiators matter?
Yes. Weather compensation can only change the temperature of the water supplied to the heating system; the radiators or underfloor heating still need to be capable of transferring enough heat into each room at those temperatures.
A radiator’s heat output changes according to the temperature of the water flowing through it and the conditions in the room.
So if a heat pump system is intended to operate at lower flow temperatures, the emitters need to be capable of delivering the heat each room requires at those temperatures.
This is why heat loss, radiator sizing, flow temperature and weather compensation are connected.
Changing one part of the system can affect another.
The system has to be considered as a whole.
Does weather compensation save energy?
Weather compensation can help a well-designed heating system avoid operating at unnecessarily high flow temperatures when the home doesn’t need them.
For heat pumps, lower flow temperatures can support more efficient operation.
But weather compensation shouldn’t be treated as a guaranteed percentage saving.
The outcome depends on factors including the home, system design, emitter sizing, settings, desired indoor temperatures and how the heating is used.
The more useful principle is this:
Don’t ask the heating system to work harder than the home requires.
Weather compensation is one way of helping it do that.
Why commissioning matters
Installing weather compensation isn’t the end of the process.
The system still needs to be configured appropriately.
That means understanding how the designed heating curve performs in the actual home.
Does the home remain comfortable as outdoor temperatures change?
Is the system delivering unnecessarily high flow temperatures?
Does it maintain the desired conditions during colder weather?
Are rooms behaving as expected?
Commissioning is where the design becomes a working heating system.
And in some cases, further optimisation can refine that operation as the system experiences different conditions.
This is an important part of thoughtful heating engineering.
A setting isn’t successful because a number has been entered into a controller.
It’s successful because the home behaves as intended.
The clever part is what you don’t notice
There is plenty of engineering behind weather compensation.
Outdoor temperature.
Heat loss.
Heating curves.
Flow temperatures.
Emitter outputs.
Controls.
Commissioning.
But none of those things are what the homeowner ultimately wants.
Imagine instead that it’s early in the morning.
Yesterday was mild.
Overnight, the temperature outside fell considerably.
You walk downstairs.
The kitchen feels just as comfortable as you expected.
You make coffee.
And you don’t touch the thermostat.
That is the point.
Weather compensation isn’t really about responding to the weather. It’s about helping your home respond so that you don’t have to.
Frequently asked questions
Do all heat pumps have weather compensation?
Not necessarily. Weather compensation depends on the heat pump, its controls and how the heating system has been designed and configured.
Where weather compensation is available, it can allow the system to adjust its flow temperature as outdoor conditions change, rather than operating at the same flow temperature regardless of how much heat the home needs.
Where does weather compensation get the outdoor temperature from?
A weather compensation system needs information about the temperature outside. Depending on the system and controls, this may come from an outdoor temperature sensor or another source of outdoor temperature data.
The controls then use that information, together with the configured heating curve, to determine how the heating system should respond.
Can weather compensation work with radiators?
Yes. Weather compensation can be used with heating systems that use radiators, provided the system has been designed and configured appropriately.
As the flow temperature changes, the amount of heat a radiator can deliver also changes. The radiators therefore need to be capable of providing the heat each room requires at the flow temperatures the system is designed to use.
This is why radiator sizing, room-by-room heat loss and weather compensation need to be considered together.
How do you know if a weather compensation curve is set correctly?
A well-configured weather compensation curve should allow the heating system to maintain comfortable indoor conditions as the outdoor temperature changes, without routinely using higher flow temperatures than necessary.
If the home struggles to remain comfortable during colder weather, the curve may not be providing enough heat — although other aspects of the heating system could also be responsible. If the home consistently becomes warmer than intended or the system operates at unnecessarily high flow temperatures, further adjustment may be appropriate.
The important measure isn’t the curve setting itself. It’s how the whole heating system performs in the home.
Should you adjust the weather compensation curve yourself?
Small adjustments may be possible on some heating systems, but there isn’t a universal weather compensation setting that every homeowner should copy.
The appropriate heating curve depends on factors including the home’s heat loss, the radiators or underfloor heating, the required indoor temperatures and the design of the heating system.
If the home isn’t remaining comfortable or you’re unsure whether the system is operating as intended, it is better to understand the cause before making significant changes to the heating curve.
Weather compensation is only part of the system
Weather compensation works best when it is considered alongside the home’s heat loss, room-by-room heating requirements, radiators or underfloor heating, flow temperatures and controls.
That is why Adlår approaches heating as a complete system — designed around the home, configured to work together and commissioned around the comfort it needs to create.
