Why Refrigerant Lines Are High Risk
Refrigerant suction lines operate at some of the lowest temperatures found in building services pipework — typically between -10°C and +10°C depending on the refrigerant and system operating conditions. In a typical UK plant room or roof-mounted installation, the pipe surface temperature can be 20–30°C below the ambient air temperature.
At these temperatures, condensation is not a risk — it is a certainty unless the insulation system is correctly specified and installed. The dew point of typical UK ambient air at 20°C and 60% relative humidity is approximately 12°C. A refrigerant suction line at 5°C is well below this threshold.
The Consequences of Inadequate Insulation
Condensation on refrigerant pipework causes a cascade of problems:
- Efficiency loss — heat gain on the suction line reduces system COP and increases energy consumption
- Compressor damage — liquid refrigerant returning to the compressor causes mechanical damage
- Corrosion — persistent moisture causes corrosion of copper pipework and fittings
- Water damage — condensate dripping from uninsulated or poorly insulated lines causes damage to ceilings, walls and electrical equipment
- Warranty voidance — most heat pump and refrigeration manufacturers void warranties where insulation requirements have not been met
Manufacturer Requirements vs BS 5422
For refrigerant pipework, two sets of requirements apply simultaneously and both must be satisfied:
BS 5422:2011 provides minimum insulation thickness for refrigerant pipework based on pipe outside diameter and operating temperature. These are the regulatory minimum values for UK installations.
Heat pump and refrigeration manufacturer specifications often require specific insulation products, minimum wall thicknesses and installation methods. These requirements are set to protect the equipment warranty and ensure correct system operation. Where manufacturer requirements exceed BS 5422, the manufacturer's specification takes precedence.
Always check the equipment manufacturer's installation manual before specifying insulation for refrigerant lines. This is particularly important for heat pump installations subject to MCS certification.
Correct Insulation for Refrigerant Lines
Closed-cell elastomeric foam is the only insulation type suitable for refrigerant suction lines without additional vapour barrier protection. Products such as Armaflex EVO provide:
- Very low water vapour permeability (µ ≥ 7,000 for Armaflex EVO)
- Integral vapour barrier — no additional wrapping required on most applications
- Flexibility for installation on complex pipework runs
- Compatibility with all common refrigerants
- Compliance with BS 5422 and most manufacturer specifications
Polyethylene foam, mineral wool and fibreglass are not suitable for refrigerant suction lines. Their high vapour permeability allows moisture to migrate through the insulation to the cold pipe surface, causing rapid deterioration and condensation failure.
Specifying the Correct Thickness
Thickness for refrigerant pipework depends on the pipe outside diameter, the suction line operating temperature and the ambient conditions. As a starting point:
| Suction Line Temp | Pipe OD | Minimum Thickness (BS 5422) |
|---|---|---|
| +5°C | 15mm | 19mm |
| +5°C | 22mm | 25mm |
| -5°C | 15mm | 25mm |
| -5°C | 22mm | 32mm |
| -10°C | 22mm | 32mm |
Always verify against BS 5422 Table 4 and the equipment manufacturer's specification. In high-humidity environments, additional thickness beyond BS 5422 minimums is recommended.
Installation Requirements
Refrigerant line insulation demands the same rigorous installation standards as chilled water pipework, with particular attention to:
Joint sealing — every longitudinal seam and butt joint must be glued with compatible elastomeric foam adhesive. On refrigerant lines, an unglued joint will allow moisture ingress within weeks in typical ambient conditions.
Fittings and valves — all service valves, Schrader valves, sight glasses and filter driers must be insulated. These are common failure points where condensation forms and corrosion begins.
Pipe penetrations — where refrigerant lines pass through walls or floors, seal the penetration to prevent warm, humid air from reaching the cold pipe surface behind the insulation.
Outdoor sections — where refrigerant lines run externally between indoor and outdoor units, use UV-resistant insulation or provide approved cladding. Standard elastomeric foam degrades rapidly when exposed to UV radiation.
Discharge lines — while discharge lines operate at high temperature and do not present a condensation risk, they should be insulated for personnel protection and energy efficiency. Standard heating pipework insulation is appropriate for discharge lines.
Heat Pump Refrigerant Lines and MCS
For heat pump installations subject to MCS certification, refrigerant line insulation must comply with both BS 5422 and the heat pump manufacturer's installation requirements. MCS-certified installers are responsible for ensuring insulation is correctly specified and installed as part of the certification process.
Failure to insulate refrigerant lines correctly can affect MCS certification and eligibility for the Boiler Upgrade Scheme grant.
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