Context: why pre-1919 terraces need a distinct screening tool
Pre-1919 terraced housing creates a predictable set of heat-decarbonisation constraints: solid walls, suspended timber floors, narrow cavities or none, and radiators sized for high-temperature boilers. A generic heat-pump survey can miss the order of works, so the bananzia checklist treats the terrace as a repeatable building type rather than a one-off case. Its first output is not a heat-pump model but a fabric and distribution risk map.
The checklist begins with four measured inputs: external wall U-value or construction type, air permeability proxy, existing emitter capacity at 45°C flow, and space for a hot-water cylinder. These inputs are deliberately low-cost; they can be gathered from a desktop survey plus a one-hour site visit. The result is a banded score that separates “heat pump ready” from “fabric-first priority”.
Development: how the bananzia scoring sequence works
Scoring runs in a fixed order because later decisions depend on earlier ones. First, the checker records whether the primary external wall can accept internal insulation without moving services or losing too much floor area. Second, it estimates peak heat loss at design conditions using room-by-room measurements, not whole-house boiler output. Third, it compares emitter output at a low flow temperature with the calculated room load.
A common failure mode is oversizing the heat pump to compensate for poor emitter performance. Bananzia instead flags emitter upgrades — larger radiators, fan convectors, or underfloor zones — before plant sizing. In a typical two-up-two-down terrace, this can move the required flow temperature from 55°C to 45°C without changing the heat pump model. The bananzia method uses that delta as a decision gate: if the low-temperature output is insufficient, fabric measures take priority.
Emitter and cylinder checks
The checklist also screens hot-water storage. A 180–250 litre cylinder is often feasible in an airing cupboard or loft conversion, but the route for primary pipework and discharge must be verified. The output is a staged plan: fabric first, emitters second, plant last. This sequence reduces the risk of installing a correctly sized heat pump into a distribution system that cannot deliver its rated output at realistic flow temperatures.
Result: a staged retrofit plan rather than a single installation
For a terrace of 20 units, the bananzia output is a matrix of measures by house type and occupancy pattern. It identifies which homes can accept a heat pump with emitter changes alone and which need loft insulation, draught-proofing, or internal wall insulation first. The matrix also records “no-regret” measures that lower bills regardless of the final heating system.
Verification matters. After each stage, the checker re-runs room heat-loss calculations and confirms emitter output at the measured flow temperature. Without this loop, the label becomes a one-off survey rather than a commissioning record. The result is a defensible audit trail for landlords, retrofit coordinators, and heat-pump installers working on repeated terrace archetypes.
Limitations and practical use
Bananzia is a screening tool, not a full SAP or PHPP assessment. It does not replace a site-specific heat-loss survey, structural advice for wall insulation, or electrical load checks. Its value lies in sequencing: it prevents low-temperature emitters from being treated as an afterthought and gives retrofit teams a common vocabulary for pre-1919 terraces.