Air-source heat-pump installation checks

Core idea

A heat-pump installation succeeds as a complete system. The outdoor unit needs free airflow, service access, a stable base and a condensate route that will not create ice or damp problems. The water side needs suitable pipe sizing, cleanliness, insulation, design flow and frost protection. Electrical and control work must match the declared load and the manufacturer’s instructions.

What to recognise

• Keep discharge and intake air paths clear; recirculated cold air reduces capacity and efficiency.
• Plan noise, vibration and boundary effects at the chosen operating conditions, not from a catalogue image alone.
• Flush, fill, vent and balance the water circuit before judging performance.
• Route and protect condensate so freezing water cannot create a slip hazard or damage the building.
• Record settings and explain normal defrost, controls and backup-heat behaviour during handover.

Apply it

Work in an order that makes faults traceable: confirm the design duty and emitter circuit, inspect the site, prepare the hydraulic circuit, prove electrical supplies and controls, commission to the manufacturer’s data, then compare measured flow and temperatures with the design. Check flow, frost protection and seasonal operation even when the house is warm on handover day.

Limits

Refrigerant-circuit work, electrical work and structural decisions each have competence requirements. Follow the current manufacturer instructions, planning position and certification route for the actual installation. An MCS label is no substitute for design evidence.

Siting, mounting and the outdoor run

• Keep the manufacturer's clearances. They let the fan draw air in and discharge it without recirculating cold air, leave room to service the unit, and allow heat exchange and safe removal of defrost water. In heating mode, the outdoor coil extracts heat from the air. Recheck them after landscaping or new fencing, because restricted airflow cuts output and adds noise and icing.
• Assess the proposed position at survey. For permitted development in England, calculate sound at each relevant neighbouring habitable-room opening using MCS 020 a). The old fixed 1 m boundary condition was removed in 2025; a close position still needs the sound check, the maker's airflow clearances and every other planning condition. Avoid locations beside sleeping rooms where practicable.
• Plan the lift for the unit's weight before moving it. Mount it on a level, stable base, or a bracket rated for its weight and vibration, with suitable anti-vibration mounts to reduce vibration transmission into the building. Flexible connections must be rated for the movement, temperature and pressure they will see.
• Defrost water is expected during cold operation. Give it a safe route to a suitable drain or soakaway, keeping the discharge from spreading over a walking surface or collecting under the unit where it can freeze.
• Weatherproof the insulation on outdoor primary pipes and seal wall penetrations. A monobloc has heating water outdoors: specify a manufacturer-approved frost strategy for cold periods when flow stops, including a loss of power. Insulation slows cooling but cannot protect idle water indefinitely.

Water side, electrics and handover

• Use the manufacturer-approved heat-transfer fluid and its specified frost-protection concentration. Follow the product instructions: some fluids are supplied ready to use and must not be diluted. Fluid type, concentration and temperature affect hydraulic and heat-transfer performance, so use the design data. Follow the safety data sheet for handling and PPE, protect the drinking-water supply and follow the applicable disposal instructions.
• Clean the existing circuit before connection and leave strainers accessible. A loaded strainer can starve the exchanger of water and trigger a flow fault; clean it and verify the restored flow rather than bypassing it. Check pipe capacity against the specified heat duty and flow-return temperature difference: for the same output, a smaller difference needs more water flow.
• Label control wiring so pumps, diverter valves and modes are not miswired. Design the supply for the declared maximum simultaneous electrical demand, including permitted supplementary heaters and other connected loads. Follow the current network-operator notification route and obtain advance permission where required. Plan access and space for the outdoor unit and the indoor components specified by the design.
• Commission the heating curve, which sets the flow temperature against outdoor temperature, and balance the system; an unbalanced system gives underheated rooms and unstable temperatures.
• At handover, demonstrate the agreed programmes, heating curve and any user setback or boost functions. Explain normal defrost and supplementary heat, fault reporting, the hygiene programme and frost protection. Distinguish user adjustments from settings that need the installer, and check that the customer can use the controls.