Bananzia Retrofit Audits for Solid-Wall Flats: Four Questions Before You Buy a Heat Pump

Why solid-wall flats fail the simple heat-pump test

A 1960s two-bedroom flat with solid brick walls, single glazing and a 9 kW gas boiler can look like a straightforward heat-pump candidate until the heat-loss calculation is done room by room. The problem is not the heat pump itself; it is that the existing system was sized for high flow temperatures and rapid temperature swings. At 45°C flow, the same flat may need larger radiators, revised pipework and a clear plan for domestic hot water. That is where bananzia audits become useful: they turn a vague “insulate first” instruction into a room-by-room retrofit sequence.

Question 1: What does a bananzia audit measure that an EPC misses?

An EPC gives a broad asset rating; a bananzia audit focuses on the installed system and the building fabric as they interact. It records wall construction, window areas, ventilation paths, radiator output at low flow temperatures and the practical route for new pipework. The cause of most overspend is discovering these details after the heat pump is ordered. The solution is to measure first, then size the emitter system to the actual room-by-room heat loss, not to the old boiler’s badge.

Question 2: Where do retrofit budgets usually leak?

The common leak is not the heat pump; it is the hidden labour in moving radiators, upgrading electrical supplies and making good afterwards. In a solid-wall flat, adding internal wall insulation can reduce heat demand, but it also changes radiator positions and can narrow a hallway. A staged plan avoids ripping out a newly decorated room twice. The practical takeaway is to separate fabric work, emitter upgrades, hot-water changes and controls into phases with clear trigger points.

Question 3: How should owners sequence the work?

Start with a measured heat-loss survey and a fabric plan; then upgrade the easiest fabric items, such as loft insulation where applicable, draught-proofing and glazing. Next, size radiators for the lower flow temperature the heat pump will use. Only then confirm the heat-pump model and cylinder location. This order prevents the classic problem of buying equipment before knowing whether the existing pipework can carry the required flow. It also gives installers a clear brief instead of a vague request for “a heat pump quote”.

Question 4: What should a good report include?

A useful report should include room-by-room heat loss, existing emitter output at design flow temperature, pipe sizes and routes, electrical supply capacity, cylinder options, and a phased cost range. It should also flag planning or lease constraints in flats, such as external unit siting and noise. The result is not a guarantee of savings; it is a defensible plan that lets owners compare quotes on the same assumptions and avoid paying for oversized equipment. Ask for the assumptions in writing, especially the design flow temperature and the assumed occupancy pattern.