Cities without boilers: The rise of ambient heat networks

Heating infrastructure is in the spotlight, as regulatory and geopolitical shifts spark a rethink of our energy needs. Amid fossil fuel shortages and rising prices, a real alternative to the ubiquitous gas boiler is needed. Meanwhile, the long-awaited Warm Homes Plan and Future Homes Standard mean heat pumps will become the default solution for both new and existing homes by the end of the decade.

The shift away from boilers is vital for achieving net zero, while ensuring heating remains affordable. Yet, amongst the homebuilding sector, there are still unanswered questions about the best way to comply with the new rules and attain a more secure energy future.

While air source heat pumps have become the catch-all solution for rural and suburban areas, dense urban environments and multi-occupancy buildings present a much bigger challenge. Issues around space, noise, electrical capacity and system design mean monobloc air-to-water units are simply not viable in most cities.

In the UK, this presents a significant hurdle to decarbonisation. As one of the most urbanised countries in the world, nearly 85% of the population lives in towns and cities, and over a fifth of homes are flats, apartments, or maisonettes, rising to over half in London. Decarbonising cities is not only pivotal to reaching net zero by 2050, but will help with energy security and health, given gas boilers are now the top source of air pollution in Central London.

A new approach to heating in cities 

Achieving this transition means treating cities as a new heating infrastructure challenge, rather than an extension of the rural and suburban approach. Exhaust air heat pumps offer one solution and are now increasingly popular for urban developments. Their compact size and ability to recover heat from a building’s ventilation system (typically kitchens or bathrooms) make them a good fit for well-insulated flats and apartments. They also offer ventilation, making them ideal for combating mould, which has moved up the housing agenda following the introduction of Awaab’s Law in 2025.

But another option has emerged, which not only works with urban challenges but harnesses what makes cities unique. As urban areas expand, so does the waste heat created by residential and commercial buildings, offices, data centres and industries. Rather than allowing this to be wasted and add to the carbon footprint, it can be captured and repurposed, using water-to-water heat pumps to transfer thermal energy via ambient heat loops and a circular heating economy.

Ambient heat loops – low-temperature district heating and cooling systems, also known as fifth-generation heat networks – typically operate at low temperatures between 10°C and 30°C. This means they offer unparalleled efficiency levels of over 400%, generating significantly lower heat losses than high-temperature, fourth-generation networks, which operate at only 35 to 45% efficiency, depending on their length and size, temperature and levels of insulation.

By creating a thermal loop, fifth-generation networks drive a significant reduction in energy demand for a whole city. Water-to-water networks also act like thermal batteries to optimise energy use during periods of low electricity prices, while maximising the output of renewable energy sources.

With the increase in extreme temperatures in cities and the strengthening of Part O regulations on overheating, fifth-generation networks can play an important role in cooling city homes in hot weather. Using active cooling to pull heat from residential spaces and return it to the network is one option, alongside passive cooling for networks that include ground-source systems, which use colder ground temperatures for even more efficient cooling.

Density is a strength, not a weakness

To take advantage of all this potential, housing developers and the building community must start thinking differently, from day one of the development process. Fifth-generation heat networks require changes to the underlying infrastructure as well as the technology in people’s homes to harness the value ambient loops offer. This means heating must come not as an afterthought, but as a core consideration of the infrastructure specification, with stakeholders across the city and energy landscape working together. As energy challenges continue, it is increasingly looking like the smartest way forward.

Challenge always comes with opportunity, and in the case of cities and heating infrastructure, density is a strength and not a weakness. Heating and cooling should be viewed not as a problem to solve in individual homes or even individual buildings, but as a circular economy, where waste heat is always stored and reused when and where it is needed. The technology is available now – it is the time to make it happen.