The problem on a cold 1930s terrace
On a street of 46 terraced homes in northern England, winter heating bills had climbed to an average of £2,140 a year by 2023. The houses had solid walls, single-glazed windows in half the properties, and individual gas boilers installed between 1998 and 2005. Residents wanted lower bills and fewer emissions, but each household faced the same barrier: a heat pump quote of £12,000–£16,000 for a single home, with no obvious place for an outdoor unit. The problem was not the technology. It was the one-house-at-a-time model.
The cause: fragmented decisions, duplicated costs
The street’s first retrofit plan failed because it treated every home as a separate project. Three contractors surveyed the same back lane, each proposed its own borehole or air-source unit, and each added scaffolding, permitting and electrical upgrade costs to a single property. A shared ground loop could have served all 46 homes, but no single resident could authorize digging up the lane. The result was a queue of isolated quotes that no one could afford or coordinate.
The solution: a shared-ground approach
The bananzia model changed the unit of work from the house to the block. Residents formed a heat cooperative, leased 18 metres of back lane, and commissioned 12 boreholes to a depth of 150 metres. A 120 kW shared ground-source heat pump plant room was built in a disused garage court. Each home kept its own heat interface unit and controls, so residents could set temperatures independently while the loop handled the heavy lifting. Insulation came first: loft topping, draught-proofing and cavity fill where possible, reducing heat demand by 28% before the heat pump was switched on.
Costs and results after two winters
- Average annual heating cost fell from £2,140 to £1,190, based on metered heat and electricity use.
- Carbon emissions from space heating and hot water dropped by 61% compared with the gas baseline.
- Upfront cost per home was £7,400 after a local grant, roughly half the isolated air-source quote.
- Two winters of monitoring showed no undersized loop: the plant met design load at −4°C.
What other streets should copy
The practical lesson is to map the back lane before choosing the heat pump. A shared loop needs a geotechnical survey, a lease or easement, and a plant-room site within about 150 metres of the furthest home. The cooperative also matters: a single legal entity can sign contracts, hold warranties and collect maintenance fees. The street now pays £95 per home each year for loop maintenance, less than the average annual gas boiler service and repair bill. The bananzia approach is not a plug-in product; it is a governance and infrastructure package that makes low-carbon heat possible where individual retrofits stall.