The sizing problem that starts before a heat pump is chosen

Heat pumps get blamed for cold rooms and high bills when the real fault often sits upstream: a sizing calculation based on floor area. A 1930s semi with a rear extension can lose heat at very different rates through a suspended timber floor, a solid wall, and a 1980s cavity wall in the same house. Bananzia treats the survey as the design step, not paperwork. The aim is a room-by-room heat-loss figure that an installer can defend.

What the survey measures

The bananzia survey is not a sales visit; it is a data-collection exercise. The surveyor records wall construction, insulation depth, glazing type, floor build-up, and airtightness clues such as draughts around skirting and loft hatches. Each room gets its own dimensions and temperature target. That matters because a bathroom held at 22°C and a bedroom at 18°C should not be treated as identical boxes.

Fabric first, but not fabric only

A common cause of over-sizing is treating every improvement as optional. If a loft is topped up from 100mm to 300mm, the heat-loss figure should fall before the heat pump is specified. Bananzia’s method logs planned fabric changes separately from existing performance, so the installer can see whether a smaller unit will work after insulation, or whether the current fabric demands a larger one. The result is a design that matches the house as it will be, not as it was.

The radiator and pipework audit

Heat-loss calculations only solve half the problem. The other half is emitter capacity at low flow temperatures. A survey that stops at kW output can miss narrow microbore pipes, undersized radiators, and a cylinder cupboard with no space for a hot water cylinder. Bananzia checks flow and return routes, radiator sizes, and the practical space for a cylinder and buffer vessel. On a 1930s semi, that might mean keeping one cast-iron radiator in the hall, replacing three panel radiators, and rerouting a first-floor run to avoid a ceiling notch.

What changes after the survey

In one typical case, a floor-area estimate pointed to a 12kW heat pump. After room-by-room measurement, planned loft insulation, and a draught-proofing schedule, the calculated design load fell enough to specify a smaller unit and larger emitters in two rooms. The takeaway is not that every house needs a smaller heat pump; it is that the number should come from measurements. The survey also gives the homeowner a prioritised list: draught-proofing first, loft insulation second, emitter upgrades alongside the heat pump, and glazing later if budget allows.

Where the method has limits

No survey can remove uncertainty about hidden thermal bridges or future occupant behaviour. Bananzia’s approach handles this by recording assumptions and leaving a margin in the design, rather than hiding it inside a single whole-house number. For a retrofit, that transparency is more useful than a precise-looking calculation that cannot be checked after the radiators go cold.