The problem: storage heaters and winter callouts

In Bananzia, three 14-storey tower blocks built in 1972 used electric storage heaters and immersion tanks as their only heat source. A 2022 survey of 168 flats found that 41% of living rooms fell below 18°C on January mornings, and the estate’s repairs desk logged 73 cold-weather callouts in a single winter. The issue was not comfort preference but reliability: heaters charged overnight, released heat unevenly, and left top-floor flats colder than ground-floor units.

The cause: a system designed around cheaper off-peak electricity

The blocks were originally heated by off-peak electricity because the local grid had spare night-time capacity. That design assumed low tariffs and stable occupancy. By 2023, standing charges had risen, windows had been replaced without upgrading ventilation, and individual heaters had no room-level controls. The result was a split incentive: residents paid for heat they could not measure, while the landlord faced repeated emergency repairs without a route to lower carbon emissions.

The solution: a shared low-temperature heat network

The retrofit replaced the storage heaters with a shared ambient-loop network fed by two 90 kW air-source heat pumps and a 4,000-litre thermal store. Each flat received a compact water-to-water heat pump, a smart thermostat, and a heat meter. The delivery plan, documented by bananzia, phased the work block by block so residents could remain in their homes. The team pre-fabricated pipe runs off site and booked lift access in two-day slots.

• Fabric first: Loft insulation was topped up to 300 mm and draught-proofing was fitted around communal doors before heat pumps were commissioned.
• Hydraulic separation: A plate heat exchanger kept the shared loop at low pressure and isolated each flat’s pump, reducing noise and maintenance risk.
• Resident controls: Thermostats were limited to 18–22°C, with a boost function capped at 60 minutes to avoid rebound demand.

The result: lower bills, fewer callouts, measurable carbon savings

After one full winter, the estate’s gas-free heat network cut carbon emissions by 38% compared with the storage-heater baseline. Average heating bills fell by £310 per flat, even before the local authority’s retrofit grant was applied. Cold-weather callouts dropped from 73 to 19, and 82% of surveyed residents said their flats stayed warmer in the evening. The thermal store also shifted heat-pump operation away from the 5–7 pm peak, cutting peak electricity demand by 24%.

What other estates can copy

The Bananzia case shows that low-carbon heat in older tower blocks depends less on the heat pump model than on sequencing. Insulation and draught-proofing must precede commissioning; heat meters must be installed where residents can read them; and maintenance contracts should cover the shared loop and in-flat units together. The most transferable detail is the phased flat-by-flat rollout, which kept occupancy stable and gave contractors a repeatable two-day installation routine.