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Load compensation

If you’re thinking about upgrading your heating system to improve your comfort, and reduce your energy bills, you might have heard the phrase ‘load compensation’ and be wondering what on earth it is! Load compensators are one of the four energy saving devices recognised by the Boiler Plus regulations. They often get confused with weather compensators. So, in this blog, we’ll explain the similarities and differences between weather compensation and load compensation and explain the factors that will help to decide which one would work best for you.

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A puppy on a sofa next to a thermometer.Are you thinking about upgrading your heating system to improve your comfort? And reduce your energy bills? If so, you might have heard the phrase ‘load compensation’ and be wondering what on earth it is!

Load compensators are one of four energy saving devices recognised by the Boiler Plus regulations.

Under Boiler Plus, all new combi boilers are required to have one of four energy saving features fitted. This is all part of the Government’s plan to achieve the UK’s carbon reduction target of net-zero by 2050.

Two of the energy saving devices are load compensation and weather compensation devices. And there’s often a lot of confusion between the two.

So, in this blog, we’ll explain the similarities and differences between weather compensation and load compensation. And explain the factors that will help to decide which one would work best for you.

The good news is, that both of these devices can help you to save money on your fuel bills; as well as reducing your carbon footprint.

What is weather compensation?

A diagram of weather compensation.The Heating and Hotwater Industry Council (HHIC) defines ‘weather compensation’ as: a control function which maintains internal temperatures; by varying the flow temperature from the heat generator relative to the measured outside temperature.

In other words, weather compensators monitor both the temperature inside your home; and the temperature outside; and adjust your boiler’s operation accordingly.

They maintain the temperature in your home by varying your boiler’s flow temperature; depending on what the measured outdoor temperature is.

Weather matters when it comes to heating your home, because of heat loss. The heat generated by your boiler will get lost through your walls and roof faster on a cold day; compared to a warmer one.

A weather compensator monitors the outdoor temperature. It tells your boiler to increase or decrease its output to precisely match the heat loss caused by the weather.

This means that your home will always be at a comfortable and consistent temperature; without your boiler cycling on and off, saving you energy.

What is load compensation?

Load compensation controls work in a similar way to weather compensation. They too use intelligent communication between temperature sensors and your boiler.

But unlike weather compensators, which use an external sensor; load compensation controls use an internal sensor to achieve your desired indoor temperature.

They do this by measuring the difference between the current temperature in your room; and the desired temperature that you’ve set. The controller then tells your boiler to increase or decrease its output to precisely close the gap.

If your desired temperature is dramatically different from the current room temperature; the load compensator tells the boiler to increase its flow temperature to the maximum. As the room temperature gets closer to your desired temperature, the boiler is told to reduce its flow temperature. 

How do weather and load compensators save energy?

Both weather and load compensation controls keep your boiler running at a consistently low flow temperature all the time. Whilst this might sound counterintuitive when you’re trying to save energy, there are two main energy saving advantages to this.

Saving energy by preventing boiler cycling

Firstly, it avoids your boiler from constantly cycling on and off.

Now you might be thinking that switching your boiler off would save energy. Because we’re always being told to switch devices off; and not just leave them on standby when we’re not using them.

But this doesn’t apply to heating your home.

When you think about it, stop-starting anything is hard-work, and the same is true for your boiler. It takes much more energy to heat up an entire house from a very cold start; than to just maintain its temperature.

Think of it as being like boiling a pan of water on a gas hob.

If you put cold water into a pan; you’ll need a high flame; and a lot of gas to get the water to boil. But once it’s boiling, you can turn the flame down low, and keep the water hot.

If you turn the gas off completely and let your water get cold; you would have to turn the flame up high and waste a lot more gas; than if you had just let it tick over at a lower temperature.

The same applies for your boiler. It burns less gas (saving energy) and keeps your home comfortable by not constantly fluctuating between being hot and cold.

Not only that, but the lifespan of your boiler will also be extended. Because just like stop-starting a car, boiler cycling puts stress on boiler components.

Saving energy by optimising condensing mode

Running your boiler at a lower flow temperature also more efficient because your boiler can run in condensing mode.

So, what is condensing mode?

All central heating systems work by sending hot water to your radiators in a loop. When the water goes out from your boiler, it’s called ‘the flow’. When it comes back from your radiators, it’s called ‘the return’.

Modern condensing boilers need the return to be below the dew point of the flue gases to be efficient.

When the temperature of the return is less than 54 degrees C; the boiler runs in ‘condensing mode’.

This sweet-spot in condensing mode is when the boiler starts to recover its lost heat; by turning the returned heat back into water on its second heat exchanger.

But most boilers don’t hit this efficient mode because their operating temperature is set too high. And so the return temperature of the water is too high for the boiler to condense.

The boiler will still work, but it doesn’t condense and won’t reach its maximum efficiency.

Compensation controls allow your boiler to operate in condensing mode; because its output is never higher than it needs to be, saving energy and money on your heating bills.

What are the differences between weather and load compensation?

As we’ve seen, load compensation works in a similar way to weather compensation. But the difference is that it reacts to the internal, rather than the external temperature.

Another difference is that weather compensation is more of a proactive approach than load compensation; because it alters the radiator output before your home drops in temperature.

Load compensation is more reactive than weather compensation; because it jumps into action as soon as the temperature in your home drops or increases.

Although this might sound less desirable than weather compensation, there is an advantage to this.

Load compensation can adjust your heating when you have an internal heat source on; like your oven on full blast; or if you have solar gains because of a conservatory; or lots of windows.

Which is better – Weather or Load Compensation?

A woman thinkingThere is no ‘right’ answer to this question because it really comes down to your individual circumstances.

But, in general, The Heating People favour weather compensation over load compensation. This is because it offers the biggest efficiency gain (up to 30% off your energy bills, according to Viessmann). And is a simple technology to integrate.

Whether load or weather compensation is the best option for you though, will depend on a range of factors, including:

How you use your home

A happy family at home.How often you are at home is a very important factor to consider when choosing between weather and load compensation.

If you work away from home; or are out of the house for long hours; or have irregular working patterns; load compensation might be the better choice for you.

After all, there’s no point heating your home to comfortable levels when nobody is home. And you’ll want to heat it as quickly as possible when someone is.

Where different heating patterns are in use; the more reactive option of load compensation is preferable. This ensures fast heat-up times following extended off periods.

The HHIC explains that weather compensation controls generally perform best where continuous heating is being used; or for an extended period “once” a day.

The size and layout of your home

When weather compensation is used, room temperatures are based on heat loss. Whereas load compensation is based on one area; which may not be reflective of the needs of the rest of the home.

So, if you have a larger home; and you are opting for load compensation; the location of the internal sensor will need to be strategically placed.

But if your home is open-plan, the indoor temperature will generally be much more stable than a house with lots of separate rooms. And an internal sensor will be less susceptible to temperature swings.

A benefit of load compensation is that it will automatically adjust to changes to your home such as installing insulation; and to variations in seasonal solar gains or shading due to foliage.

Your property type

Whether you live in a terraced house; a detached hous;, or a flat; will also affect which option is better for you.

Weather compensation controls might be adversely affected when heating a flat; where there is intermittent influence from flats above; below or either side of your home.

Solar gains

‘Solar gain’ is the increase in temperature in your home which is caused by heat from the sun.

Even though the UK isn’t renowned for its sunny weather; your home will still be getting some short-wave radiation heating directly through openings such as windows; or by indirectly heating the fabric of the building.

In a room or building which is significantly affected by the heat from the sun; the heating system needs to be responsive by heating up and cooling down quickly. This is whether the more reactive, load compensation controls can be particularly useful.

The thermal mass of your home

A calculator next to a thermal image.The thermal mass of your home is another factor to consider in your choice.

If your home has little thermal mass; when you leave a door or window open; your home will cool down quickly.

In this situation, load compensation is a good option. Because it responds to these internal influences, and heats up rapidly. Meaning that you can return a more comfortable room temperature as quickly as possible.

The amount of insulation your home has

A dog next to feet in socks.If your home has good insulation; it will be more easily affected by small internal heat sources such as ovens, and hairdryers; than a property with poor insulation. This is something to consider with load compensation.

However, a lot of people in the UK are living in brick built houses without particularly great insulation. And these homes are most likely to benefit from weather compensation controls.


Final thoughts…

A piggy bank next to the ErP scale.Weather compensation is generally best where continuous heating is being used, or for an extended period “once” a day. It has the advantage that room temperatures are based on heat loss; rather than one area, which may not reflect the rest of the home’s needs.

Load compensation controls are better suited to homes with more irregular or less frequent occupation; because they are more responsive with rapid heat up, and they respond to internal heat sources.

If you want to find out more about how The Heating People can help you find what type of control is right for you; contact one of our friendly team, who will be happy to help.

You might also like our related blog: Does smart heating save money?

Useful Links:

Boiler Plus Factsheet from the government

Boiler Plus Consultation

Government report: Heat in Buildings

Government report: The ten point plan for a green revolution

The Heating and Hot Water Industry Council document on weather compensation

Installer online article: 5 myths about weather compensation

Heat Geek article on weather or load compensation