There is no universal maximum pipe length for a UK split. Small domestic systems often fall in the 15 to 30 m class, and that is only a class of limits, not your limit. The quote must use the installation manual for that outdoor unit. A longer, prettier route is irrelevant if the measured run, counted the way that manual counts bends, sits outside the figure. Extra length can also need extra refrigerant, which the installer adds at commissioning. There is no single UK maximum to copy from another install.
The outdoor unit's own pipe range
The outdoor unit is built for a range of pipe lengths and a range of height difference. Outside that range the oil and the refrigerant do not behave as the manufacturer tested. There is no single maximum to copy from another job. The price uses the manual for that outdoor unit.
A straight sleeve uses little of the allowance
The installer measures the route they will actually build. A hole straight through the wall behind the indoor unit uses little of the allowance. A run through a loft, down a townhouse, and along a side passage can leave the class before the condenser is in the quiet spot you wanted. Each manufacturer counts the run in its own way. Two installers quoting different lengths for the same sketch should show you the tape, not a slogan.
A closer wall, a second outdoor unit, or another model
If the preferred outdoor wall is too far, the choices are a closer wall, a second outdoor unit, or a different model whose manual allows the run. Stretching the pipes and hoping is how compressors fail later. A pre-charged outdoor unit usually includes enough refrigerant for a stated length. Beyond that, the manual says how much to add. That calculation is part of commissioning by an F-gas certified company. It is not a bottle from a shop. Energy Saving Trust describes these systems as air-to-air heat pumps. The pipe limit is still a manufacturer limit.
Frequently asked questions
Is 15 m or 30 m the maximum in the UK?
Neither. Small splits are often in that class. The maximum is the figure in the manual for the outdoor unit on your price. There is no universal maximum.
Do bends count as extra length?
On many manuals, yes. The installer should apply that model's method, including the rise and the bends if the manual treats bends as extra length. Do not add a metre per bend from a forum and treat it as the rule.
Can the installer add gas so the pipes can be longer than the manual?
No. Extra refrigerant is only for length the manual already allows. Beyond the maximum, that outdoor unit is the wrong choice.
Can a long horizontal run still fail on height?
Height difference has its own line in the same manual. A long horizontal run with a big rise can fail even when neither number, looked at alone, seems huge.
Does a lawful wall that is too far still work?
In England the outdoor spot also has to satisfy Planning Portal conditions. A lawful wall that is too far for the pipes is still the wrong wall for that model.
Core buying guides
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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.