Air Conditioning Pipework and Condensate Drainage Explained
Air conditioning pipework is the copper pair, cables and drain that join the indoor unit to the outdoor unit. It is also the usual source of visible trunking, extra labour and unexpected mess. Distance, wall type and how the water gets away all show up on your quote after the survey.
By British Air Conditioners
What air conditioning pipework connects the indoor and outdoor unit
A split system is two boxes and a short list of services between them. Insulated copper pipes carry refrigerant. An interconnecting cable carries control and power signals. A condensate pipe carries water away from the indoor coil. Those three usually pass through one core-drilled hole, then run together to the outdoor unit.
The refrigerant pipes are not garden hose. They have to be the diameter the manufacturer specifies, kept clean and dry, and joined by an F-Gas certified engineer. Handling refrigerant is legally restricted to F-Gas certified engineers. Our vetted contractors are F-Gas certified for that work. A neat-looking pipe with an untested joint is how leaks and failed warranties start.
MyJobQuote's 2026 installation walk-through describes the on-site sequence as indoor unit, hole through the wall, outdoor unit, then pipes and cables connected and leak-tested before the system is put into service. That leak test and evacuation step is why "the boxes are on the wall" is not the same as "it is finished."
If you want the wider install sequence around this work, see what an air conditioning installation involves.
Trunking: internal vs external routing
Trunking is the plastic cover you see on many UK outside walls. It hides the insulated pipes and keeps ultraviolet light and footballs off them. External trunking is usually quicker and cheaper than chasing. You will see a rectangular run from the hole down to the condenser, unless the indoor and outdoor units sit back to back with almost no visible pipe.
Internal routing hides more of the pipe but means cupboards, boxing or chasing. Chasing period plaster is slow, dusty and often a separate making-good job. MyJobQuote's 2026 extra-costs table puts a plaster patch at around £100 and decorating at around £400 a room. Those are directory averages for follow-on work, not a promise that your hallway will cost that. If you want invisible pipes, ask for that scope on the quote rather than hoping the contractor will chase for free.
Back-to-back installs, where the indoor unit sits on an outside wall directly opposite the condenser, keep pipework short. MyJobQuote's 2026 saving tips say a simpler layout like that can reduce pipework and labour. It is not always possible. A chimney breast or a window in the way is why the survey exists.
Condensate drainage and where the water goes
When the indoor unit cools, it wrings water out of the air. That water has to go somewhere. The usual options are a gravity run to the outside, a connection into a suitable waste, or a condensate pump that lifts the water to a drain.
Gravity is quiet and simple if the indoor unit is high enough and the pipe can fall all the way. A dip, a sag in the trunking, or a run that goes uphill will overflow into the room. That is a fitting error, not a mysterious leak from the refrigerant circuit.
MyJobQuote's 2026 guide says that if gravity drainage is not possible, a condensate pump may be needed, with extra parts and installation. Pumps hum and they can fail. You should know if your quote includes one. Dripping onto a public path, a neighbour's window, or a socket is not an acceptable outlet.
In winter, outdoor condensate from a unit that is also used for heating can freeze on a path. The contractor should think about where that water lands, not only where the pipe exits the wall.
Maximum pipe runs and why distance matters
Every model has a maximum pipe length and a maximum height difference. Go beyond it and the manufacturer will not support the system. Extra length also means extra copper, extra insulation, extra time, and often extra refrigerant to charge. MyJobQuote's 2026 guide lists pipe run length and trunking as a direct cost factor: longer routes usually mean higher labour and more finishing work.
As a manufacturer example, Daikin's 2018 installer reference guide for one common split range states a maximum allowable pipe length of 30 m, a minimum of 3 m, and a maximum height difference of 20 m. That is not a universal UK limit. A different indoor and outdoor pair will have a different table. Your contractor should quote against the model they intend to fit.
A long run is sometimes still the right choice if it puts the outdoor unit somewhere quieter or easier to service. The quote should show that trade-off. A cheap total that quietly assumes a 3 m back-to-back run will not survive contact with a rear garden condenser serving a front bedroom.
If the units will be far apart, say so when you request a quote so the surveyor is not surprised by a three-storey drop.
Routing through period properties and solid walls
Solid brick and stone take longer to core than a timber frame. MyJobQuote's 2026 guide says solid brick or concrete walls can take longer to drill and make good than timber or plasterboard. In a Victorian terrace that often means one carefully placed hole, not a row of experimental openings.
Period features change the route. Cornicing, shutters, window reveals and lime plaster are easy to damage and slow to repair. Internal trunking in a cupboard or at high level is often kinder than chasing a chimney breast. External trunking on a rear elevation is often kinder than either, if you can accept seeing it from the garden.
Listed buildings and conservation areas add a consent layer. The contractor can suggest a discreet route. They cannot tell you that your specific property is exempt. Confirm with your local planning authority, and with the conservation officer if you have one, before anyone drills a front wall.
In Bristol, as in other cities with mixed Georgian, Victorian and new-build stock, the same indoor unit can be a two-hour pipe run in one house and a two-day making-good job in the next. That difference belongs on the quote.
How pipework affects your quote
The kit on the wall is only part of the price. Pipe length, number of indoor units, trunking versus chasing, a pump versus gravity, and access at height all move labour. MyJobQuote's 2026 guide also flags flats, long carries, ladders and scaffold as extras. If the outdoor unit is on a flat roof, getting pipework there is a logistics cost as well as a copper cost.
Read the quote for metreage, not only for the model name. If two contractors propose very different totals, compare the pipe route on the drawing. One may be quoting a rear-wall condenser. The other may be quoting a front-bedroom unit served from a distant back garden, with a pump and painted trunking.
Do not try to shorten the job by buying pre-charged DIY kits and asking someone unqualified to flare the joints. Refrigerant handling is legally restricted to F-Gas certified engineers. A failed joint is both a leak and a paperwork problem.
When you want the route priced against your walls, request a quote. The survey is where pipework stops being theoretical. If you are still choosing who should do that work, how to choose an air conditioning installer in the UK covers the checks to make before you sign.
FAQ
Will there be visible pipes on my wall?
Often yes, if the pipes run externally in trunking. A back-to-back layout can leave almost nothing on show. Internal routing or chasing hides more pipe and usually costs more in labour and making-good. Ask to see the proposed route on a sketch at survey, and make sure the quote says trunking, chasing or a hidden cupboard run.
Where does the water drain to?
Condensate from the indoor unit should run by gravity to the outside or into a suitable waste, or be lifted by a pump if a fall is impossible. It should not drip onto a neighbour, a path, or an electrical point. Ask the contractor to show the outlet. If a pump is required, it should be itemised on the quote.
Can pipes run under floors?
Sometimes, if there is a void, a route that can be insulated, and a way to inspect joints later. Underfloor runs are not a default in solid-floor houses. Pipes still have to meet the manufacturer's length limits, and joints still need an F-Gas certified engineer. Raise it at survey rather than assuming a hidden route exists.
What if the units are far apart?
The manufacturer sets a maximum pipe length and height difference for each model. Longer runs cost more in copper, insulation, time and often extra refrigerant. Daikin's 2018 guide for one split range caps pipe length at 30 m and height difference at 20 m. Other models differ. The quote should reflect a distant route, not a short one.