Core drilling is the round hole that lets the pipes, cable and drain leave the room. On a normal brick or block wall the installer's own drill does it, and that hole sits inside the install price. A specialist core, for thick stone, reinforced concrete, or a wall the fitter cannot drill, is a separate line. In 2026 illustrations that specialist visit is often in the low hundreds, and more with access, a scan for hidden services, or careful listed fabric. That is an illustration, not a tariff.
A sleeve behind the indoor unit
A short sleeve through a cavity wall behind the indoor unit is everyday work. Dust is controlled, the sleeve is sealed, and the pipes pass through with a fall for the drain where gravity is the plan. You should see that included, not added as a surprise on the day.
Stone, concrete and a wall you cannot name
Flint, thick sandstone, a concrete lintel zone, or a wall you cannot identify is when a core-drilling firm attends with a rig. They need water or dust extraction, time, and a clear instruction about where services might be. The air conditioning price should name them or tell you the hole is assumed to be ordinary.
Ground floor with the van outside
One hole at ground floor, with the van outside, is the lower band. Several holes, a drill from a scaffold, a party wall, or a mansion-block wall with unknown makeup moves it. Scanning or a careful hand search for cables adds time and is cheaper than a struck pipe.
- Standard brick cores are usually inside the install.
- Stone, concrete and awkward walls can need a specialist.
- The sleeve still has to be sealed and made good.
Insulation crushed by a tight hole
Diameter follows the pipe insulation and the drain, not a hope that a smaller hole will be kinder. A hole that is too tight crushes insulation and the drain. The installer specifies the size. Listed fabric and decorative stone can need a conservator rather than a fast core, which is a different cost again.
A neat hole is not a commissioned system
Drilling is not commissioning. The F-gas engineer still pressure tests, evacuates and charges. A neat hole with a leaking joint is unfinished. Making good the face of the wall may be in the install or left to you. Ask which. The sleeve, the seal and who makes good the finish should be named, so the core is not only a round of dust.
The hole has to land on a lawful outdoor spot
In England the outdoor unit position is a Planning Portal question even when the hole is the hard part. The hole should land where the pipes can reach a lawful condenser spot.
Frequently asked questions
Can I drill the hole myself to save money?
Leave it to the installer or a driller they direct. A hole in the wrong place, or through a service, costs more than the visit. The sleeve position has to suit the pipes and the drain.
Core buying guides
Start with these high-intent guides, then dig into the rest of the library.
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.