Weather Compensation vs Load Compensation

Your heating needs to work harder on a freezing January morning than on a mild autumn afternoon. It also needs less heat once your living room has reached a comfortable temperature.

But how does your boiler know how much heat to provide?

That’s where load compensation and weather compensation come in. Both can adjust the temperature of the water going to your radiators, helping a compatible boiler match the amount of heat your home needs.

Load compensation uses indoor temperature feedback. Weather compensation uses the temperature outside. Some controls combine both.

The difference sounds small, but it affects how your heating responds throughout the day. Here’s what each does, what you might notice at home, and what to check before choosing one.

First, what is boiler flow temperature?

Flow temperature is the temperature of the water leaving your boiler to heat your radiators or underfloor heating. It’s different from the room temperature you set on your thermostat.

You might want your living room at 20°C, for example. The water travelling through the radiators needs to be hotter than that to warm the room.

The question is how hot that water needs to be.

A higher flow temperature allows radiators to release more heat. A lower flow temperature provides gentler heating and can help a condensing boiler operate more efficiently, provided your home still gets warm enough.

Lower flow temperatures can also mean cooler water returning to the boiler. That helps it recover more heat from the exhaust gases through condensation. Energy Saving Trust explains how flow temperature affects efficiency.

Compensation controls adjust that heating temperature automatically as demand changes.

How does load compensation work?

Load compensation looks at the difference between the temperature measured indoors and the temperature you’ve asked for.

Imagine your thermostat is set to 20°C, but the room is currently 16°C. There’s a fair amount of warming up to do, so the control can request a higher heating flow temperature.

As the room approaches 20°C, it can reduce the requested temperature. Your radiators then provide less heat as the room gets closer to being comfortable.

That gradual adjustment can help reduce overshooting, where the heating brings a room up to temperature but it continues getting warmer than you wanted. Worcester Bosch describes this adjustment in its guide to boiler controls.

What happens when sunshine warms the room?

Picture a sunny afternoon when the living room warms up even though it’s cold outside.

An indoor control can detect that rise in temperature and reduce the heating demand. The same principle applies when cooking, appliances or a room full of people add warmth.

However, it only knows what’s happening where the temperature is measured.

If your thermostat sits in a sunny living room while the bedrooms stay cold, its reading may not represent the rest of the house. Positioning matters: follow the control’s installation guidance and ask your installer how the thermostat and radiator valves should work together.

How does weather compensation work?

Weather compensation uses outdoor temperature to work out an appropriate heating flow temperature.

As it gets colder outside, your home generally loses heat faster. The control responds by raising the temperature of the heating water. When the weather becomes milder, it lowers it.

This means it can respond to an outdoor temperature change before your indoor thermostat detects a drop in room temperature.

Depending on the system, the outdoor reading comes from a sensor fitted outside or weather information supplied over the internet. An outdoor sensor isn’t always necessary. Vaillant explains both approaches in its weather compensation guide.

What is a heating curve?

A heating curve tells the control how the heating flow temperature should change as the outdoor temperature rises or falls.

Think of it as a setting that matches your heating to your home.

A house that loses heat quickly may need a different curve from a well insulated home. The radiators or underfloor heating also affect the water temperature needed to keep rooms comfortable.

If the curve is too high, the system may supply hotter water than necessary. Too low, and the house may struggle to warm up in cold weather.

That’s why setting up weather compensation properly matters. Your installer should choose suitable settings and explain how they can be adjusted if the house feels consistently too warm or too cold. Viessmann’s controls guide illustrates how heating curves work.

Which is better: load or weather compensation?

Both can be useful. The best choice depends on the controls your boiler supports and how they’ll be set up in your home.

Load compensation is useful for responding to indoor changes. If sunshine or cooking regularly warms the area around your thermostat, indoor feedback allows the heating demand to adjust accordingly.

Weather compensation is useful for matching heating temperature to changing outdoor conditions. Instead of using the same heating water temperature through mild and cold weather, the system adjusts automatically.

Weather compensation alone cannot directly measure the extra warmth from cooking or sunshine indoors. Equally, a room sensor on its own cannot directly measure a sudden outdoor temperature drop.

Those differences are why combining indoor and outdoor information can be useful.

Can you have both?

Yes, with a control system designed to provide both functions.

For example, Vaillant’s sensoROOM uses load compensation alongside internet weather information through myVAILLANT connect. Worcester Bosch also lists load and weather compensation among the features of its EasyControl system when used with suitable equipment. Vaillant sensoROOM and Worcester Bosch controls brochure.

If you’re choosing a new boiler and controls together, ask about a system that can use both inputs. Your installer should explain what the proposed combination actually supports and which functions will be enabled.

Will compensation controls save money?

They can reduce energy use by helping the heating supply an appropriate amount of heat and avoiding unnecessarily high water temperatures.

The saving depends on what you have now, how well your home retains heat, your heating schedule and how the new controls are configured.

A home already running with well adjusted controls may see a different benefit from one using unnecessarily high flow temperatures.

There’s no single saving that applies to every installation. Treat any percentage or annual saving as something to investigate: what was it compared with, and do those conditions resemble your home? Vaillant also identifies insulation, system efficiency and usage habits as factors affecting savings.

Do you need a smart thermostat?

You need suitable controls, but app access alone doesn’t tell you whether a thermostat provides compensation.

A smart thermostat may let you change the temperature from your phone while still controlling a particular boiler through a simple on/off connection.

To adjust the requested flow temperature, the control and boiler need to communicate in a suitable way. Some combinations use OpenTherm; others use a manufacturer’s own communication system. Viessmann explains how OpenTherm differs from basic on/off control.

When comparing products, ask:

“Will this control adjust the flow temperature on my exact boiler model, and what connection does it need?”

That gives you a more useful answer than simply asking whether the thermostat is compatible.

Can you upgrade an existing boiler?

You may be able to add compensation controls without replacing the boiler. Start by finding the exact model and checking which controls it supports.

Ask an installer to confirm:

• Which compensation functions are available.

• Whether you need a new thermostat, receiver, gateway or outdoor sensor.

• Whether the existing wiring is suitable.

• What installation and setup are included in the price.

Energy Saving Trust identifies fitting weather or load compensation as a possible way to automate flow temperature adjustments. Whether that’s possible for your home depends on the existing equipment. Energy Saving Trust’s flow temperature guide.

If your heating also supplies a separate hot water cylinder, ask how the proposed controls will manage cylinder heating. The system needs to meet its hot water requirements as well as heating the rooms. Energy Saving Trust’s heating controls guidance.

Why might the radiators feel cooler?

With compensation controls, radiator temperature can vary during the day. That’s part of how the system adjusts its heat output.

On a mild afternoon, the radiators may feel warm. During colder weather or while bringing a cold room up to temperature, they may feel hotter.

Judge the heating by whether the rooms reach a comfortable temperature. Radiators don’t need to feel equally hot all day.

If the house stays too cold, though, ask the installer to check the settings and system performance. Compensation should help maintain comfort; you shouldn’t have to put up with rooms that never reach the temperature you’ve set.

What should you ask before buying?

Before accepting a quote for new controls, ask your installer these five questions:

1. What will this control do with my exact boiler? Ask whether it provides load compensation, weather compensation or both.

2. How will it measure outdoor temperature? Find out whether it needs a sensor or an internet connection.

3. Where will indoor temperature be measured? Discuss any rooms that are unusually sunny, cold or heated by another source.

4. Who will set it up? Confirm that the quote includes enabling the features and adjusting the settings.

5. What happens if the house feels too warm or too cold? Get a clear explanation of the adjustments you can make and when to contact the installer.

If you’re replacing your boiler, discuss the controls as part of the quote. The boiler and controls work together, so it makes sense to choose them together.