The challenge of decarbonising existing heat networks

Pete Mills, Commercial Technical Operations Manager at Worcester Bosch Commercial & Industrial, discusses the government’s net zero targets and the challenges developers will face when decarbonising existing heat networks.

In line with the government’s target to achieve net zero by 2050, heat networks are one solution proposed to help meet the UK’s decarbonisation targets in the coming years.

While the goal is to meet the net zero target through a significant reduction of GHG emissions across the whole of society, heating is a major category to address.

There are several steps that need to be tackled before we will be able to decarbonise existing heat networks.

To this effect, several trials are underway around the country, but time is not on the industry’s side since government aims to decarbonise all existing heat networks by 2035. In my opinion that is not a lot of time.

Large and small scheme developers will face issues looking into existing heat networks and will need to work around the challenges that will arise during the process.

Large and smaller heat networks

There is quite a difference in the UK between large district schemes and smaller communal heat networks, as we have many more smaller heat networks than larger ones.

At an estimate, there is something like 11,000 communal networks, comparted to 2,000 district heat networks.

Installers and manufacturers are used to running heat networks, where the bigger and wider schemes tend to be completed at a better standard. We still have a need to decarbonise on a smaller scale as many of the larger schemes have been built using Combined Heat and Power, which is fast losing its carbon savings rating.

As a result, there is a contrast between those bigger schemes and the smaller, communal heat networks.

The smaller networks tend to get designed by developers wanting to work in a particular area. However, communal heat networks do not receive the same funding possibilities, as the money is directed to larger heat networks.

These smaller ones are somehow just going to decarbonise as they are built around gas boilers currently, which makes them an obvious sector to focus in on.


I anticipate there will be some issues around converting both types of networks. For instance, some of the earlier heat networks will need to be converted to lower operating temperatures.

Improvements will need to be made on the return temperatures and the insulation levels they are getting.

The first step to achieve a net zero target is to get all heat networks operating more efficiently than they are today. As most of these schemes were oversized already, they need to be brought more into line.

The next step would be to start thinking how we can incorporate renewable technology. We know that heat pumps are the technology of choice, but we also know that they need to operate at lower temperatures (80°C to around 60 to 65°C) to meet government objectives.

In addition, there may be some space challenges with already allocated plant rooms on several smaller schemes due to space being a real premium.

Developers want to maximise the space available to the dwellings, which could present a challenge for installers and certain equipment might need to go external to cope with this.

It will be interesting to see how developers will get around this.

Hybrid systems

We might find that where we have difficulties with the schemes we will need to use hybrid systems to get good decarbonisation levels.

We have found that if you have around 40% of the heat load covered by heat pumps then you can cover an excess of 80% of your kW hours.

80% of the energy is going across to a renewable source, which will be a way to achieve a reasonable level of decarbonisation on some of these harder to do schemes.

Ultimately, it could be that the systems have a hydrogen type arrangement at some point.

Even though we have been set a timescale of 2025, we will only just see hydrogen start to develop at some sort of level as we approach closer to that date.

It will not be nationwide in the UK by then but I anticipate some of these schemes might have to limp along until such time as hydrogen can pick up the load.

There might be some schemes that are luckier and in areas where hydrogen will come in earlier then we can directly use them.

This is just another angle of what might come into play when decarbonising heat networks.