A wall-mounted split air conditioner normally has a high-level indoor unit, an outdoor unit, insulated refrigerant pipes, interconnecting cable, a condensate drain and a suitable electrical supply. A survey should settle capacity, airflow, pipe and drain routes, noise, access and permissions before work starts. Refrigerant work must be completed by appropriately qualified people and, where required, a certified company. The finished system should be tested, commissioned and handed over with operating and maintenance information.
What the installation includes
The indoor and outdoor units are only the visible parts. The installation also needs refrigerant pipework, insulation, control wiring, condensate disposal, wall penetrations, weather sealing, supports and electrical protection. Each element should be shown or described in the quotation.
A simple route through the wall behind the indoor unit can reduce visible trunking and joints. London terraces, flats and Essex extensions may instead need longer routes around structure or finishes. Long or concealed routes need service access and must remain within the equipment manufacturer's limits.
Choosing indoor and outdoor positions
The indoor unit needs clear air return and enough throw to mix air through the occupied part of the room without directing a cold draught at a bed, desk or sofa. It also needs safe access for filter cleaning and servicing.
The outdoor unit needs unrestricted airflow, stable support and access for future maintenance. Its position should account for neighbouring windows, boundaries, vibration paths and hot air recirculation. It should not be boxed into a narrow enclosure merely to hide it.
- Confirm service clearances for both units.
- Mark the pipe, cable and drain route before drilling.
- Check for concealed pipes, cables and structural constraints.
- Agree the appearance of external trunking and brackets.
What happens during installation
Competent installers mount the equipment, create and weather-seal penetrations, route services and establish a reliable drain. Refrigerant pipework is then connected and tested using procedures appropriate to the equipment and current legal requirements.
The system should be evacuated, leak checked and commissioned in accordance with the manufacturer's instructions. Electrical safety checks, operating readings, condensate testing and checks in the available modes help establish that the installation works as designed.
Permissions and handover
Planning status depends on the property and proposal. Flats, listed buildings, conservation areas and leasehold homes need particular care. England's Class G heat-pump provisions contain limits and include a condition that the unit must not be used solely for cooling.
At handover, obtain model and serial details, controls guidance, commissioning records, warranty information and relevant electrical documentation. Ask how to clean filters, where the isolator is, how condensate is routed and what maintenance the manufacturer requires.
Frequently asked questions
Can a wall-mounted indoor unit go on any wall?
No. The wall must support the unit and allow suitable airflow, service access, pipework and drainage. Concealed services and the appearance of the external route also need checking.
Does the outdoor unit have to be directly behind the indoor unit?
No, but a short direct route is often simpler. Longer routes must remain within manufacturer limits and may affect access, appearance, refrigerant charge and drainage design.
Should pipe joints be hidden permanently?
Avoid making serviceable components inaccessible. Concealed routes should be designed and recorded so inspection, leak investigation and replacement do not require unnecessary damage.
What should be tested before handover?
Checks should cover electrical safety, refrigerant integrity, condensate flow, controls, airflow and operation in relevant modes, following the manufacturer's commissioning requirements.
Related guides
Sources and further reading
How this guide was prepared
This guide was written by the Local AC Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.