Judge a heat pump installation on six checkable items: a room-by-room heat loss calculation, a stated design flow temperature of 50 °C or below, pipework sized for the flow rate, a stated reason for any buffer or volumiser (defrost volume, zoning or hydraulic separation), weather compensation active at handover, and a commissioning data pack you keep. Done right, these deliver a measured seasonal COP of 3.0 or better; field trials show poorly designed systems fall nearer 2.5.
What paperwork should exist before installation starts?
A good installer produces a room-by-room heat loss calculation to EN 12831 (or the national equivalent, such as MCS methodology in the UK) before quoting a unit size — never a per-square-metre guess. The document should list each room's heat loss at the local design outdoor temperature, the emitter fitted, and the flow temperature at which that emitter covers the loss. From it follow three numbers you should see in writing: the building's total design load, the selected heat pump capacity at design conditions, and the design flow temperature. If the capacity is far above the calculated load, ask why — oversizing causes cycling and poor efficiency and is the most common design failure. Our guide to comparing two heat pump quotes covers how to weigh competing proposals line by line.
What does a good hydraulic design look like?
Simple and low-temperature. The efficiency of any heat pump is set mainly by its flow temperature — each 1 °C reduction improves efficiency by roughly 2% — so a design that achieves 40–45 °C at design conditions through adequate emitters will outperform a 55 °C design in the same house by a double-digit margin. Pipework must carry the required flow at sensible velocity; keeping an existing microbore or 15 mm primary network without checking it is a classic shortcut. Each hydraulic component should have a stated job: a correctly piped buffer tank provides defrost volume, protects zoned systems from short-cycling and separates bivalent generators, while a badly piped one mixes flow and return — so the design should say why it is there and how it is piped.
What should happen at commissioning and handover?
Commissioning turns a plumbed system into a performing one. Expect the installer to set and record the flow rate, configure the weather compensation curve rather than leaving a fixed high temperature, set the hot water schedule and anti-legionella cycle, and brief you on why the system should run long and low rather than being switched on and off. The handover pack should contain the heat loss calculation, hydraulic scheme, commissioning sheet with recorded settings, and warranty terms.
| Checklist item | Good sign | Red flag |
|---|---|---|
| Sizing basis | Room-by-room EN 12831 calculation | "We always fit a 12 kW" |
| Design flow temperature | Stated, 50 °C or below | Not stated, or 60 °C+ |
| Buffer tank | Justified in writing, or absent | Fitted "just in case" |
| Controls at handover | Weather compensation active | Fixed flow temperature, thermostat cycling |
| Documentation | Full data pack handed over | Verbal assurances only |
| Performance | Metering or COP estimate provided | "You can't measure that" |
How do I verify performance after installation?
Measure, or at least sanity-check. The gold standard is a heat meter plus electricity meter giving a true seasonal performance factor; many units now report an internal COP estimate that is useful for trend-watching even if flattering in absolute terms. Context for your numbers: the UK's Electrification of Heat demonstration recorded a median seasonal performance factor of about 2.8 across ordinary retrofits, while well-designed installations routinely exceed 3.5. If your system sits below 2.5, something in the design or settings is wrong — our page on why a heat pump's COP is low lists the usual culprits in fixable order. Give any verdict a full winter: defrost behaviour and deep-cold performance only show themselves below zero. As a manufacturer, Solimpeks publishes capacity and COP tables across the operating map for its heat pumps precisely so installers can be held to a stated design point rather than a brochure best case.
What are the red flags that predict a bad installation?
Five recur in almost every problem system: no heat loss calculation; a quote that cannot state the design flow temperature; a buffer tank and extra pumps with no stated purpose; controls handed over in fixed-temperature mode with the advice to "use it like a boiler"; and resistance to metering or performance questions. None of these requires engineering knowledge to spot — they are questions any homeowner can ask before signing, and a competent installer answers all five without hesitation.
Frequently asked questions
What is a good measured COP for a heat pump installation?
A seasonal performance factor of 3.0 is a solid result for a radiator retrofit, 3.5 and above indicates a well-designed low-temperature system, and underfloor systems can exceed 4. Field-trial medians around 2.8 show what average design achieves — treat anything under 2.5 as a fault to investigate, not a characteristic of the technology.
Should every heat pump installation have a buffer tank?
No. A buffer is a tool for specific problems — defrost volume, zoned circuits, hydraulic separation — and a well-matched open system often runs better without one. What matters is that its presence or absence is a documented decision, and that it is piped correctly — two-port where no separation is needed — which keeps its efficiency cost to a few per cent.
Can I judge the installation before winter?
Partially. Paperwork, flow temperature, controls configuration and hot water performance can all be verified in the first week. Efficiency in defrost conditions and comfort at design temperature need a cold spell, which is why commissioning data and a metering plan matter — they let you audit the system when winter arrives.
What documents should the installer hand over?
At minimum: the room-by-room heat loss calculation, the hydraulic schematic, a commissioning record with set flow rate and weather compensation settings, user instructions, and warranty and certification paperwork. Missing documentation is itself a red flag, because every later dispute starts from what was designed versus what was delivered.