Aircon Pipe Insulation Thickness: What Keeps a Run Dry

A refrigerant line is sleeved against condensation. Whatever energy the foam saves is a small side benefit. Take the foam off a working system and the room still gets cold; what it also gets is water forming along the copper and running off it.

Only one surface matters: the outside of the foam. Refrigerant holds the copper well below room temperature the whole time the system runs. The wrap stands between the copper and the room, and foam carries heat badly, so its outer face sits closer to the room than to the metal.

Thickness is how far that outer face is held away from the cold. More foam puts more resistance between the two, so the face runs warmer; less foam lets the cold reach nearer the surface. The pipe temperature never moved.

Whether a given surface temperature is safe is not a property of the pipe. It belongs to the air standing next to it, and the line that face has to stay above is the dew point. That physics is settled in its own guide.

Two different thicknesses get quoted on the same pipe, and mixing them up is easy. Copper pipe wall thickness is metal, measured across the tube wall, and it governs what the circuit can hold. The figure on this page is foam, measured outward, and it governs what the outside of the run does in humid air.

Because the figure is set by the air the sleeve stands in, and that air changes several times on the way from an indoor head out to the ledge. One continuous pipe passes through conditions that have nothing in common.

The stretch inside a cooled bedroom has the easiest job on the route. Cooling takes moisture out of that room continuously, so the air beside the sleeve is drier than anywhere else the pipe goes. Air moves there as well, and a surface in moving air is warmed by it.

The same pipe above a false ceiling is somewhere else entirely, with identical foam on it. Nothing conditions that space. Air arrives out of the rooms below, settles, and holds whatever the weather handed it. A marginal sleeve fails there first.

Manufacturers write that step into the manual. Daikin's manual for its ducted indoor units instructs that where the temperature and humidity at the refrigerant piping sections may exceed 30°C or 80% RH, the insulation is reinforced to 20mm or thicker. Condensation may otherwise form on the surface of the insulating material. The baseline in the same maker's wall-mounted R32 split manual is a 10mm minimum foam wall on the gas line.

Neither figure carries to another job on its own. Both belong to particular models, both are tied to the line sizes in that model's own table, and the larger one is conditional on the surrounding air. Authority sits in whichever installation manual covers the equipment being fitted.

Read that condition against a ceiling void in a Singapore flat and the reinforced case stops looking unusual. Why the air here sits so close to its limit belongs to the dew point. The consequence belongs on this page: a void nobody conditions spends much of the year inside the range a manufacturer attaches its heavier specification to.

Thickness survives being written on a document. Continuity gets decided on the ladder, and that is the half which fails. A run specified correctly and executed with gaps performs at its worst point, never at its average.

Closed-cell elastomeric foam, known in the trade here as Armaflex, does two jobs at once. The body of the material resists water vapour pushing through it. Every cut, seam and butt join is a hole in that resistance.

Vapour is not a draught and does not need one. It moves toward cold, along any path nobody closed. A join held with finishing tape is shut against moving air and still open to vapour. What genuinely seals a seam is a question about the material.

The failures cluster rather than spread out. Almost all of them sit where somebody had to stop, cut, or force something through.

• •Butt joins, wherever one length of sleeve meets the next along a long run.
• •Tight bends, where foam thins on the outside of the curve and creases on the inside.
• •Clips and cable ties pulled down hard enough to crush the wall of the sleeve.
• •The wall crossing, where a sleeve gets trimmed back to get the bundle through the hole.
• •The last stretch at each unit, where foam meets a fitting and the wrap has to end.

Foam degrades fastest where it is easiest to look at, which is the one convenient fact in this subject. The outdoor length carries the entire environment at once: ultraviolet light, rain, heat, and whatever the ledge collects.

Unprotected elastomeric foam breaks down at the surface under ultraviolet light. It chalks, hardens, then splits along its length. Rain gets into the splits, and once foam has taken up water it has stopped insulating.

Manufacturers treat outdoor protection as material, not as an upgrade. Elastomeric insulation used outside is specified with a weather-resistant finish. A ledge run left as bare black foam is the specification with its outer layer missing.

The signs are readable from a window. Foam gone pale and powdery instead of black and slightly springy. A split running the length of the sleeve along its upper face. Sections shrunk back and leaving a band of copper showing, and tape unwound and hanging loose.

Bare copper outdoors is a different problem from bare copper indoors. Water forming on an outdoor line drips onto a ledge and nobody sees it. What it does instead is start corrosion on the tube and let heat into a line the system was built to keep cold.

The ledge stretch is the one length anyone can inspect without opening a finish, and the cheapest to put right. A concealed pipe run declines silently and presents as a ceiling repair; this one declines in plain sight and can be re-sleeved where it stands.

Answers to all of the following exist before any material is bought. The route is known once the layout is agreed..

Ask about the run in segments instead of as one line. A quote reading insulated pipework has priced an average. It crosses a cooled bedroom, a void, a wall and a ledge, and the sleeve has to be right in the worst of those.

Ask where the figures came from as well as what they are. Somebody working from the document covering the model can say which line size a figure belongs to, and whether the reinforced condition applies to any stretch of this route. Somebody working from memory offers one thickness.

The person choosing the foam is often not the person who wrote the quote. Material gets picked up on the morning of the install, and the choice lands with whoever is at the counter, which is why it should be settled on paper first.