How far can the outdoor unit sit from the indoor unit?

Updated September 13, 2026 · Claude AC · 2 sources cited

Contents (7)

The four numbers that decide everything
Why the limits exist at all
What a long run actually costs you
Height is the number people trip over
When the distance simply does not fit
Before you sign the quote
Frequently asked questions

Almost every quote for a wall-mounted split quietly assumes the same thing: that the outdoor unit will end up more or less behind the indoor one, with a short hop of pipe through the wall. When that assumption breaks — the flat faces an inner courtyard, the balcony is on the wrong side, the freeholder will only allow a roof or ground position, the façade you would like to drill is the one the planners protect — the conversation stops being about aesthetics and becomes mechanical. How far apart can the two boxes actually be?

There is no useful rule of thumb here, and the trade has a bad habit of offering one. The real answer is four numbers, printed in the installation manual of the exact model being fitted. Those four numbers, and nothing else, decide whether a proposed route is a normal installation, an installation with a documented supplement, or a warranty claim waiting to be refused.

The four numbers that decide everything

The number	What it governs	Typical residential mono-split
Maximum total pipe length	The longest run the manufacturer will stand behind	Commonly 15 to 30 m
Chargeless (pre-charged) length	The run already covered by the factory charge in the outdoor unit	Commonly 5 to 10 m, often 7.5 m
Additional charge per extra metre	Refrigerant weighed in beyond the pre-charged length	Commonly around 20 g per metre on R-32
Maximum height difference	Vertical separation, usually stated separately for outdoor unit above and below	Commonly 8 to 15 m, and often less in one of the two directions

To make that concrete rather than abstract: one widely sold European R-32 split series states a maximum total piping length of 30 m, a height difference of up to 15 m with the outdoor unit higher and 7.5 m with it lower, and 20 g of extra refrigerant per metre beyond the chargeless length. Another manufacturer, another capacity, another year of the same range — the figures move. Which is the entire point. Ask for the manual of the model on your quote, not for the reassurance of the person selling it.

Why the limits exist at all

Three physical constraints sit behind those numbers, and understanding them tells you which corners are safe to cut and which are not.

Pressure drop. Refrigerant moving through a long, narrow copper line loses pressure to friction. The compressor has to work against that loss, so a system at the end of its allowance delivers slightly less cooling for slightly more electricity than the same system on a three-metre run.

Oil return. The compressor’s lubricating oil does not sit politely in the compressor; some of it circulates with the refrigerant and has to find its way home. Long horizontal runs and, above all, long vertical lifts slow that return. This is why the height limit is often asymmetric, why manufacturers sometimes specify oil traps at intervals on a rise, and why a system that technically fits the length limit can still fail early if the vertical geometry was ignored.

Charge mass. More pipe holds more refrigerant. Past the chargeless length the balance of the circuit only stays right if the additional gas is weighed in on scales, in grams, to the manual’s figure. Estimating it from gauge pressure on a warm afternoon is not the same operation.

What a long run actually costs you

Three different currencies, and it is worth separating them.

Money. Insulated copper pair, trunking, fixings, the labour of chasing or boxing a route across a building, and the extra refrigerant itself. Installers price this per metre beyond an allowance included in the headline figure — typically three to five metres. As an indicative order of magnitude across European markets, each additional metre adds somewhere in the tens of euros once materials and labour are counted, so a twelve-metre route instead of a three-metre one is a few hundred euros of difference rather than a rounding error. Our guide to what it costs to install air conditioning in Europe breaks down where the rest of the quote goes.

Capacity. Manufacturers publish correction factors for long runs, and the honest summary is that the penalty is real but modest — a few per cent of capacity across a long route, not a collapse. Distrust both extremes: the fitter who says distance makes no difference at all, and the one who claims you will lose half your cooling. Neither has opened the table.

Risk surface. Every extra metre is more pipe to damage, more joints along the way, more trunking, more places where a future drill or a roof repair meets a refrigerant line. Long runs are also where under-charging quietly happens, which is why the weighed supplement must appear on the commissioning paperwork — see our guide on refrigerant, leaks and EU rules for what that document should say.

Height is the number people trip over

Length is intuitive; height is not. A fourth-floor flat with the outdoor unit standing in the ground-floor courtyard is roughly twelve metres of vertical separation before a single horizontal metre is counted, and that can sit outside the allowance of a small domestic unit in the unfavourable direction. The same arrangement in reverse — indoor unit low, condenser on the roof — is governed by a different figure in the same manual.

This is exactly where multi-splits get complicated as well, because each branch has its own minimum and maximum and the level difference between indoor units is itself limited; our guide to multi-split systems covers that geometry.

When the distance simply does not fit

Situation	Route worth exploring
Route exceeds the model’s length allowance	A different model family with a longer stated allowance, often the light-commercial version of the same range
Height difference out of range	An intermediate position for the outdoor unit — a balcony, a flat roof, a bracketed wall position partway down
Only one permitted outdoor position, several rooms	A multi-split sharing one route, rather than several long individual runs
No outdoor unit permitted at all	A wall monobloc, accepting its efficiency and noise trade-offs
The run is only long because of the indoor position	Move the indoor unit: a different wall, a floor console near the riser, often cheaper than ten metres of trunking

Before you sign the quote

Four questions, each answerable in one line by anyone who has actually planned the job: what is the total pipe run in metres on this route; what is the chargeless length of this model; how many grams of refrigerant will be weighed in beyond it, and will that figure be written on the paperwork; what is the height difference and in which direction. A fitter who has measured the route answers those in under a minute. One who has not will change the subject to the brand.

Frequently asked questions

Is a three-metre run always better than a twelve-metre one?

Mechanically, yes, slightly — less pressure drop, less refrigerant, fewer metres to go wrong. Practically, a well-executed twelve-metre run inside the manufacturer’s allowance beats a short run to a bad outdoor position where the unit recirculates its own hot air or sits under a neighbour’s window. Distance is one constraint among several, not the ranking criterion.

Will a longer pipe run raise my electricity bill?

Marginally. The efficiency penalty of a long but compliant run is a few per cent, which on a European cooling season of a few hundred kilowatt-hours is a small number of euros. Sizing, setpoint and hours of operation move the bill far more, as our guide to what air conditioning costs to run in Europe sets out.

Can the outdoor unit go on the roof, two floors up?

Only if both the total length and the height difference for that direction are inside the model’s stated limits, and only if the structure, access for servicing and any building or co-ownership consent allow it. Roof positions also need a serviceable route: a condenser that cannot safely be reached is a condenser that will not be maintained.

Who pays for the extra refrigerant on a long run?

You do, as part of the installation, and it should be itemised before the work rather than discovered afterwards. It is a legitimate, documented, weighed addition at commissioning. What is not legitimate is a request for a top-up weeks later on a standard-length run, which points to a joint that was never tight.

Can excess pipe just be coiled behind the unit?

A small surplus is routinely coiled, but a coiled surplus is still pipe: it counts towards the total length, it holds refrigerant, and a tightly wound coil at a low point can collect oil. Cutting and flaring to the length actually needed is the better job, and on a long route it is also the cheaper one.