Dew Point & Condensation Explained Simply

How to Prevent Condensation on Chilled Water & Refrigeration Pipes

Condensation on cold pipes is one of the most common insulation failures. It leads to water damage, mould growth, corrosion, and reduced thermal efficiency. Understanding dew point and how to prevent condensation is essential for any HVAC or refrigeration installer.

This guide explains the science in simple terms and gives you practical solutions.

💧 What is Condensation?

Condensation occurs when warm, moist air comes into contact with a cold surface. The air cools down, and the moisture in the air turns into liquid water droplets on the surface.

Common examples:

Water droplets on a cold drink can
Misted windows in winter
Sweating pipes in basements or plant rooms

🌡️ What is Dew Point?

The dew point is the temperature at which air becomes saturated with moisture and condensation begins to form.

Key principle:
If a surface temperature drops below the dew point, condensation will form on that surface.

Example:
Plant room at 20°C with 60% relative humidity:

Dew point = approximately 12°C
Any surface below 12°C will sweat
A chilled water pipe at 6°C WILL condense unless properly insulated

⚠️ Why Condensation is a Problem

💧 Water damage — Dripping water damages ceilings, walls, and equipment
🦠 Mould and bacteria growth — Health hazard in occupied buildings
🔩 Corrosion — Shortens pipe and equipment lifespan
⚡ Energy loss — Wet insulation loses thermal performance
🚫 System failure — Insulation becomes waterlogged and useless

✅ How to Prevent Condensation

1. Use Closed-Cell Insulation

For any pipe below ambient temperature, you MUST use closed-cell elastomeric insulation (like K-FLEX ST or SK).

Why?
Closed-cell insulation has a built-in vapour barrier that prevents moisture from penetrating the insulation and reaching the cold pipe surface.

Never use: Open-cell foam, fibreglass, or mineral wool without a vapour barrier on cold pipes.

2. Choose the Right Thickness

The insulation must be thick enough to keep the outer surface temperature above the dew point.

Rule of thumb:

Chilled water (6-12°C): 19-25 mm
Refrigeration (-30 to +10°C): 19-32 mm
Domestic cold water (5-15°C): 13 mm minimum

See full thickness guide →

3. Seal All Joints Properly

Even the best insulation will fail if joints are not sealed correctly.

Best practices:

Use K-FLEX 800 contact adhesive on all joints
Or use K-FLEX SK self-seal tubes (peel-and-stick)
Overlap joints by at least 25 mm
Seal end caps and valve covers

4. Insulate Valves, Fittings & Elbows

Don't leave gaps! Uninsulated valves, elbows, and tees are common condensation points.

Use pre-formed fittings or wrap with insulation tape and seal with adhesive.

5. Consider Ambient Conditions

High-humidity environments (basements, coastal areas, plant rooms) require thicker insulation.

If relative humidity is consistently above 70%, increase thickness by one size (e.g., 19 mm → 25 mm).

📊 Dew Point Reference Table

Air Temperature	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

🔧 Troubleshooting Condensation Problems

Problem: Insulation is sweating

Cause: Insulation is too thin or joints are not sealed

Solution: Increase thickness or re-seal all joints with adhesive

Problem: Water dripping from pipe

Cause: Gaps in insulation at valves, elbows, or fittings

Solution: Insulate all fittings and seal gaps

Problem: Insulation feels damp

Cause: Open-cell insulation or damaged vapour barrier

Solution: Replace with closed-cell elastomeric insulation

🛒 Shop Condensation-Proof Insulation

📚 Related Guides

Need help? Contact our technical team for project-specific advice.