Gas has quietly left the design brief for new residential development. The 2021 uplift to Approved Document L tightened carbon and primary-energy targets for new homes, the London Plan expects major schemes to be net zero-carbon in operation, and a decarbonising grid means electricity now wins almost every compliance calculation it enters. So the live question for developers is no longer whether to build all-electric, but which all-electric architecture to commit to. On apartment-led schemes the choice usually narrows to two: a low-temperature hot water (LTHW) heat network fed by central air source heat pumps, or an ambient-loop network with the heat pumps distributed through the building. On a single-line schematic they look like cousins. In plant space, riser design, overheating behaviour, metering and resident experience, they produce very different buildings.
What is an ambient-loop heat network?
An ambient loop is a shared water circuit that runs around a building, or across a whole site, at close to environmental temperature, typically somewhere in the region of 10°C to 25°C, with a compact water-to-water heat pump in each apartment lifting that low-grade heat to space-heating and hot-water temperature at the point of use. The central plant, usually roof-mounted air source heat pumps, does deliberately light work: it holds the loop within its temperature band rather than manufacturing hot water for the whole building.
That inversion defines everything else about the system: the temperature lift moves out of the energy centre and into the dwelling. Because the network runs near room temperature, it sheds almost no heat into risers and corridors. The loop is also a shared thermal resource rather than a one-way delivery pipe, so a well-configured system can move energy between dwellings: an apartment rejecting heat in cooling mode warms the loop for a neighbour calling for heating. It is the architecture AMF is engineering at Cyprus Beckton, where 211 apartments are served by an all-electric ambient-loop air source heat pump network within our Stage 4-5 mechanical scope.
How traditional LTHW networks work, and where the heat goes
A conventional communal or district system generates heat centrally and distributes it hot. An energy centre (today increasingly heat-pump-led rather than gas-fired) feeds LTHW risers, and each apartment draws its heat through a heat interface unit (HIU). Inside the HIU, plate heat exchangers hydraulically separate the dwelling from the primary network: one plate serves the apartment’s heating circuit, while another generates domestic hot water instantaneously as the tap runs, so there is no cylinder in the flat and the water-hygiene regime stays simple.
The price of that simplicity is paid in distribution. Hot pipework threading through a residential building sheds heat continuously: energy generated at the plant, recovered through residents’ tariffs, and deposited into corridors whether anyone wants it or not. Driving those losses down through insulation, low flow temperatures and disciplined return temperatures is a central concern of CIBSE’s CP1 Heat Networks Code of Practice, the benchmark the London Plan expects networks to match. CP1 sets standards across the whole life of a network, from feasibility through design and commissioning to operation. A heat network is an energy business the developer is creating, and CP1 treats it that way.
That business is now formally regulated: Ofgem became the regulator for heat networks on 27 January 2026, bringing rules on billing, customer service, complaints handling and protections for vulnerable consumers, with operators and suppliers required to register. Where residents buy heat, as they do on an HIU-based network, someone is running that regulated business for the life of the building. On an ambient loop, residents typically pay for the electricity their own heat pump consumes through their domestic supply instead, which changes the billing model and may change the regulatory position; it should be tested scheme by scheme, early.
Why does Part O change the heat network conversation?
Because distribution losses are internal heat gains, and overheating is now a building regulation in its own right. Approved Document O requires new residential buildings in England to demonstrate overheating mitigation, and most apartment schemes evidence this through CIBSE TM59 dynamic thermal modelling. Communal corridors wrapped around warm LTHW risers are a well-known trouble spot: heat that escapes the network in July arrives precisely where the model can least afford it.
An ambient loop changes the starting position of that analysis. With the network at near-room temperature, riser and corridor gains largely disappear and the TM59 assessment begins from a cooler baseline. The distributed heat pumps also open a route to comfort cooling or peak-lopping where modelling shows residual risk. Many in-apartment units are reversible, and the loop is already in place to absorb rejected heat. Part O’s hierarchy still applies: fabric, shading, orientation and ventilation come first, and mechanical cooling must be justified, never assumed. But on dense urban sites where noise or air quality constrains openable windows, an architecture that can deliver cooling through pipework already in the building is a materially stronger position than one that cannot.
Ambient loop or LTHW: which suits your scheme?
There is no universal winner. The choice follows the site. The London Plan’s heating hierarchy directs schemes in Heat Network Priority Areas to connect to existing or planned district networks first, which favours a conventional low-temperature communal arrangement ready to accept an external heat supply. Where no network is coming (and heat network zoning under the Energy Act 2023 will progressively formalise where one is), the two all-electric architectures compete on engineering merit.
The LTHW route concentrates plant, refrigerant and maintenance in the energy centre, keeps apartments cylinder-free and compact, and presents residents with familiar, silent HIUs. The ambient route all but eliminates network losses and corridor gains, enables energy sharing and a credible cooling pathway, but puts a heat pump, and usually a hot water cylinder, in every apartment, with consequences for layouts, acoustics, maintenance access and the electrical distribution strategy that must be resolved before spatial coordination begins.
AMF has delivered both. Alongside the ambient-loop network at Cyprus Beckton, our all-electric portfolio includes Orion Park in West Ealing (95 apartments including a Higher-Risk Building under the Building Safety Act 2022) and High Path Estate Phase 2 in South Wimbledon, where 147 gas-free homes form part of a regeneration of around 2,000 homes. The recurring lesson across all three is that the architecture decision belongs at Stage 2 or 3, not Stage 4: it fixes riser allocations, plant space, apartment layouts and incoming electrical capacity long before the first duct is drawn.
Getting the decision right
If you are weighing an all-electric strategy for a residential scheme, or have inherited a planning commitment and need to know what it means for cost, space and programme, AMF MEP can test both architectures against your site, run the TM59 and Part L analysis that settles the compliance questions, and carry the chosen system from RIBA Stage 3 through to handover with executive oversight throughout. Talk to us before the architecture fixes itself.