Trunking is the cover over pipes, cable and sometimes the drain between the indoor and outdoor unit. A short run of standard white trunking is a small materials line inside a normal install. The cost appears when the route is long, when you want it painted or hidden, or when the alternative is opening finished rooms. In 2026 illustrations, a long visible route with careful making good can move a job by high hundreds compared with a three-metre straight run. Survey the route before you compare badges. An F-gas certified company joints the pipes. The firm that plans a route you can live with is worth more than a slimmer fascia.
A short back-to-back run against a long trail
The easy install leaves the outdoor unit on the other side of the wall from the indoor unit. Trunking is brief, outside, and obvious only if you stare at it. Price differences between brands will not hide inside that metre. The plastic on a short run is minor. A condenser on the rear wall and an indoor unit on the front bedroom means a journey along eaves, through a cupboard, or down a stair. Every bend is labour. Metres and bends are the labour. Internal boxing, lifting floors, and decorating afterwards often cost more than the trunking lid. Making good and decorating can exceed the plastic cover. Colour-matched or recessed routes cost more than white lids. Ask for the route in metres and in rooms crossed.
Include a modest trunking allowance inside the usual high-hundreds-to-low-thousands single-split illustration when the run is short. When the quote grows a 10 or 15 metre trail around a terrace, expect the job to step up by high hundreds, more if floors come up or a listed interior cannot take surface plastic. A lower quote with the route still to be agreed is not lower yet. Pin the path. Two installers looking at different walls are not selling the same trunking. Pipes can sometimes run inside a cavity or a boxed chase, if it is buildable and still serviceable. Chasing a finished listed room can cost more than surface trunking and may need consent.
A lid that still has to drain and stay reachable
White PVC on a brick terrace is normal and honest. On a street-facing listed front it may be unacceptable, which pushes you to a rear route and a longer bill. Do not bury pipes in a way the next engineer cannot reach. Flare joints and the outdoor valves need access. A pretty box that traps heat or blocks the outdoor fan is a fault. Drain falls should not be sacrificed to a neat horizontal lid. If the pretty route cannot fall, you are in pump territory as well. Pick the route that drains, breathes at the outdoor unit, and looks acceptable. The shortest line that drips on a neighbour is not the bargain. Planning Portal notes still apply to the outdoor end of that pipe, whatever the trunking costs. GOV.UK F-gas rules apply to whoever charges it.
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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.