Why Both Lines Need Insulating
Heat pump refrigerant pipework has two sides with opposite requirements. The suction line runs cold (below ambient) and will condense without closed-cell insulation. The discharge line runs hot and loses energy without insulation. Both lines need insulating — skipping the discharge line is a common mistake that reduces system efficiency.
Thickness by Line Type
| Line | Temperature | Recommended Product | Thickness |
|---|---|---|---|
| Suction line (indoor) | -10 to +10°C | K-FLEX ST or SK | 13–19mm |
| Suction line (outdoor) | -10 to +10°C | K-FLEX Solar HT | 19mm |
| Discharge line (indoor) | 40–65°C | K-FLEX ST or SK | 13mm |
| Discharge line (outdoor) | 40–65°C | K-FLEX Solar HT | 13mm |
In high-humidity environments, increase suction line thickness to 19mm regardless of location.
Material: Why K-FLEX Elastomeric
K-FLEX elastomeric covers the full temperature range of heat pump pipework (-50°C to +105°C) in a single material. The closed-cell structure provides a built-in vapour barrier on the suction line — no additional wrapping needed. Flexible enough to install on the tight bends typical around outdoor units. The SK self-seal range has a factory-applied adhesive strip for fast installation without separate adhesive.
For outdoor runs, K-FLEX Solar HT is UV-stabilised. Standard elastomeric will degrade and crack in direct sunlight within months — don't use it outdoors without cladding protection.
Installation Best Practices
Seal all joints — use K-FLEX K-420 contact adhesive on all butt joints and longitudinal seams, or use SK self-seal. An unsealed joint on the suction line is a direct vapour path to the cold pipe surface.
Insulate through wall penetrations — maintain continuous insulation from indoor unit to outdoor unit. Gaps at wall penetrations are common condensation and heat loss points.
Use insulated pipe clips — standard metal clips compress the insulation and create thermal bridges. Use clips designed for insulated pipework that support the insulation without crushing it.
Don't stretch or compress — install insulation at its natural length. Stretched insulation is thinner than specified and may not keep the surface above dew point.
Common Mistakes
- Only insulating the suction line — discharge line needs it too
- Using open-cell foam — absorbs moisture and fails on cold pipes
- Leaving gaps at joints, valves, or wall penetrations
- Using standard elastomeric outdoors — UV degradation within months
- Compressing insulation at pipe clips — creates thermal bridges
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