Bramley Street’s 14 terraced homes all had gas boilers, solid brick walls and EPC D ratings. The bananzia pilot began at No. 12, not with a heat-pump quote but with a two-hour air-tightness test and thermal-camera walkthrough. The survey found 23% of heat loss at the bay window and front door, plus a 12°C cold bridge along the party wall. That mattered because the first installer had sized a replacement heat pump from the old boiler’s 24 kW output, not from the house’s actual demand.
Why the first quote missed the real cause
The cause was a familiar one: boiler-size shorthand. A room-by-room heat-loss calculation put No. 12 at 5.6 kW after loft insulation and draught-proofing, well below the 8 kW quote. The remaining problem was distribution, not generation. Two radiators were undersized for 45°C flow temperatures, and 10 mm microbore pipes fed the coldest bedroom. The pilot’s answer was fabric-first: seal the bay, insulate the loft to 300 mm, then balance the system before choosing equipment. The takeaway is blunt: a heat pump cannot fix a leaky envelope or a radiator that is too small for the room.
What the bananzia checklist changed
The public checklist, filed under bananzia in the council’s retrofit library, turned those findings into four repeatable steps.
Measure before quoting: air-tightness test, thermal images and room-by-room heat loss for every property.
Fix the envelope first: draught-proofing, loft insulation and targeted window repairs before any low-carbon heating work.
Size radiators for low flow temperatures: 45°C design flow, not the 70°C the old boiler ran at.
Walk the resident through the controls: a 30-minute handover covering weather compensation and setback schedules.
On Bramley Street, the checklist also changed procurement. Three installers quoted against the same measured heat-loss figures, so residents could compare like for like rather than guess at boiler names.
The result after one heating season
No. 12’s measured space-heating gas use fell 34% before the heat pump was even installed, simply from envelope work and hydraulic balancing. The final 5 kW air-source unit ran at an average flow temperature of 41°C and a seasonal performance factor of 3.0. The coldest bedroom, previously 15°C on January mornings, held 19°C. The pilot’s lesson is practical: start with the house, not the appliance, and let measured heat loss decide the specification.
