Air-conditioning refrigerant line: how much pipe and insulation it needs

The refrigerant line is the stretch most often forgotten to measure properly in an air-conditioning installation: it is not the straight-line distance between the two units but the real route through walls and ceiling, and that changes the material quote more than it seems.

How to measure the copper pipe

The refrigerant line connects the indoor unit to the outdoor one through insulated copper pipe. You must measure the real distance, including the route through walls and ceiling, not the straight-line distance — and add 15% waste to that real measurement.

Calculation example: for a measured distance of 8 metres: 8 × 1.15 = 9.2 lm of copper pipe to buy. This is the same calculation the PresupuestoYa calculator applies automatically for the AC Technician trade.

The limit that can't be exceeded without penalty

Most domestic splits allow up to 10-15 metres of pipework. Beyond that limit, the unit's power drops or extra gas has to be added — so on installations with the outdoor unit far away, it's wise to check the unit's data sheet before quoting the installation.

Insulation is not optional

Copper pipe must be thermally insulated to avoid condensation and loss of performance, with an elastomeric foam sleeve (armaflex type):

• 13 mm thick: the minimum recommended in humid climates.
• 19 mm thick: in very humid areas or long outdoor runs, to stop the sleeve "sweating" and dripping onto walls or false ceilings.

A 10% waste allowance is added to the length to insulate for joints.

What gets forgotten when quoting alongside the pipe

• Support or bracket for the outdoor unit: always check the strength of the wall before anchoring — on slight facades or ETICS insulation, chemical anchors are needed or a floor stand should be considered. Anti-vibration mounts reduce the transmission of vibration and noise to the home.
• Vacuum and leak test: a mandatory process before starting up the unit, which removes air and moisture from the circuit. A good vacuum drops below 500 microns and holds stable for at least 10-15 minutes without rising — skipping it (or doing it badly) is the most common cause of early faults from moisture in the refrigerant circuit.

Frequently asked questions

Is the refrigerant line measured in a straight line between the two units? No: the real route through walls and ceiling must be measured, which is almost always longer than the straight-line distance.

What happens if the refrigerant line exceeds 15 metres? The unit's power may drop or extra gas has to be added — always check the split's data sheet before installing a long line.

Why is the vacuum so important before starting the unit? Because it removes air and moisture from the circuit. Skipping it is the most common cause of early faults from moisture in the refrigerant system.

Conclusion

Measuring the real route of the refrigerant line —not the straight-line distance— and choosing the right insulation thickness for the climate is what separates an air-conditioning installation that performs to its data sheet from one that loses efficiency from day one. Automating the calculation with the waste allowance included gives an accurate material quote.