What is Condensation?
Condensation occurs when warm, moist air contacts a surface that is cooler than the air's dew point. The moisture in the air turns to liquid water on that surface. On cold pipes, this means dripping water, wet insulation, corrosion, and mould — all of which are preventable with the right insulation specified and installed correctly.
What is Dew Point?
The dew point is the temperature at which air becomes saturated and condensation begins to form. If a pipe surface is below the dew point of the surrounding air, it will sweat.
Example: A plant room at 20°C with 60% relative humidity has a dew point of approximately 12°C. A chilled water pipe running at 6°C will condense unless the insulation keeps the outer surface above 12°C.
Dew Point Reference Table
| Air Temp | Relative Humidity | Dew Point |
|---|---|---|
| 20°C | 50% | 9°C |
| 20°C | 60% | 12°C |
| 20°C | 70% | 14°C |
| 25°C | 50% | 14°C |
| 25°C | 60% | 17°C |
| 25°C | 70% | 19°C |
How to Prevent Condensation
1. Use Closed-Cell Insulation
For any pipe running below ambient temperature, you must use closed-cell elastomeric insulation. The closed-cell structure acts as a built-in vapour barrier, preventing moisture from migrating through the insulation to the cold pipe surface. Open-cell foam, fibreglass, and mineral wool without a vapour barrier will absorb moisture and fail on cold pipes.
K-FLEX ST and SK elastomeric insulation are the standard choice for chilled water and refrigeration applications.
2. Use the Right Thickness
The insulation must be thick enough to keep the outer surface above the dew point at the highest expected ambient humidity. As a guide:
- Chilled water (6–12°C): 19–25mm
- Refrigeration (-30 to +10°C): 19–32mm
- Domestic cold water (5–15°C): 13mm minimum
- High-humidity environments (RH consistently above 70%): increase by one size
3. Seal All Joints
An unsealed joint is a vapour path straight to the pipe surface. Use K-FLEX K-420 contact adhesive on all butt joints and longitudinal seams, overlapping by at least 25mm. Alternatively, use K-FLEX SK self-seal tube which has a factory-applied adhesive strip — peel and press.
4. Insulate Valves, Fittings, and Elbows
Uninsulated valves and fittings are the most common condensation points on an otherwise well-insulated system. Use pre-formed fitting covers or wrap with insulation sheet and seal all edges with adhesive.
5. Account for Ambient Conditions
Basements, coastal locations, and plant rooms with poor ventilation have higher humidity than standard indoor environments. Increase insulation thickness accordingly and pay extra attention to joint sealing.
Troubleshooting
| Problem | Likely Cause | Solution |
|---|---|---|
| Insulation sweating | Too thin or joints not sealed | Increase thickness or re-seal all joints |
| Water dripping from pipe | Gaps at valves, elbows, or fittings | Insulate all fittings and seal gaps |
| Insulation feels damp inside | Open-cell material or damaged vapour barrier | Replace with closed-cell elastomeric |
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