Chilled Water Pipe Insulation — Complete UK Guide

Introduction

Chilled water pipe insulation is one of the most technically demanding applications in building services. Get it wrong and you face dripping pipework, saturated insulation, corrosion, and structural damage. Get it right and the insulation will perform reliably for 20+ years.

This guide covers the correct materials, thicknesses, and installation techniques for chilled water pipe insulation in the UK — from small fan coil unit connections to large-diameter primary distribution mains.

Why Chilled Water Pipe Insulation Is Different

Chilled water pipes operate at temperatures below ambient — typically 6–12°C flow and 12–16°C return. In a typical UK plant room or ceiling void at 20–25°C with moderate humidity, the pipe surface is well below the dew point of the surrounding air. Without insulation, condensation forms continuously on the pipe surface.

The primary purpose of chilled water pipe insulation is condensation control, not heat loss reduction. This changes the specification requirements significantly compared to heating pipework. See: Vapour Barriers for Pipe Insulation — Complete Guide.

The Vapour Barrier Requirement

For chilled water insulation to work, the vapour barrier must be continuous and unbroken across the entire pipe run. Water vapour in the surrounding air will always migrate towards the cold pipe surface — the vapour barrier is the only thing stopping it.

This means:

• Only closed-cell insulation with an integral vapour barrier is suitable — open-cell materials (mineral wool, polyethylene foam) are not appropriate for chilled water without a separate vapour barrier jacket
• All joints must be fully bonded with adhesive — any gap in the vapour barrier is a failure point
• All fittings, valves, and tees must be fully insulated — no exceptions

Choosing the Right Material

Armaflex EVO — the standard specification

Armaflex EVO is the most widely specified material for chilled water pipe insulation in the UK. Key properties: λ = 0.033 W/m·K, μ ≥ 10,000, Microban antimicrobial protection, Euroclass B-s2,d0. The Microban protection is particularly valuable in ceiling voids and plant rooms where mould growth on insulation surfaces is a risk. See: Armaflex vs K-Flex — Which Should You Choose?

K-Flex ST — acceptable alternative

K-Flex ST (λ = 0.036 W/m·K, μ ≥ 7,000) is an acceptable alternative to Armaflex EVO for most chilled water applications. Its lower μ value provides less margin of safety in high-humidity environments.

Foil-faced phenolic foam (Kooltherm) — where space is constrained

Kingspan Kooltherm achieves BS5422 compliance at thinner wall thicknesses than elastomeric foam due to its lower λ value (≈ 0.022–0.025 W/m·K). However, the foil facing must be maintained intact at all joints — any breach creates a complete vapour barrier failure. See: Foil-Faced vs Elastomeric Foam — Which Should You Choose?

Materials not suitable for chilled water

Mineral wool and polyethylene foam are not suitable for chilled water without a separate vapour barrier jacket. See: Mineral Wool Pipe Insulation for appropriate applications.

BS5422 Thickness Requirements for Chilled Water

BS5422 provides condensation control thickness tables for chilled water pipework. The required thickness depends on the pipe temperature, the ambient conditions, and the insulation λ value. See: BS5422 Explained — The Complete Guide and What Thickness Pipe Insulation Do I Need?

Chilled water (10°C flow, ambient 25°C / 60% RH) — Armaflex EVO (λ 0.033):

Chilled water (6°C flow, ambient 25°C / 70% RH — high humidity):

Always refer to BS5422 and the insulation manufacturer’s condensation control tables for compliant specification. For pool plant rooms and other extreme humidity environments, greater thicknesses are required — see: Pipe Insulation for Swimming Pools.

Installation Requirements

The installation requirements for chilled water pipe insulation are more demanding than for heating pipework because the vapour barrier must be continuous and unbroken. See: How to Cut and Install Pipe Insulation — Complete Guide.

• Bond all longitudinal seams with Armaflex 520 adhesive — both faces, allow to become tacky, press firmly
• Bond all butt joints with adhesive
• Insulate all fittings, valves, and tees — no gaps
• Use insulated pipe supports with a thermal break — standard pipe clamps create cold bridges
• Seal all penetrations through walls and floors

Frequently Asked Questions

What insulation should I use on chilled water pipes?

Closed-cell elastomeric foam — Armaflex EVO or K-Flex ST. Do not use polyethylene foam or mineral wool without a separate vapour barrier jacket.

What thickness insulation do I need on chilled water pipes?

For 10°C chilled water at 25°C / 60% RH ambient, 19–25mm Armaflex EVO is typically required depending on pipe size. For colder water or higher humidity, 25–38mm is required. Always verify against BS5422.

Why is my chilled water pipe insulation dripping?

The most likely cause is insufficient insulation thickness for the actual ambient conditions, or a failed vapour barrier at joints or fittings. Check every seam, joint, and fitting for gaps. Replace any failed sections with correctly specified Armaflex EVO at the thickness calculated for the actual ambient conditions.

Can I use foil-faced insulation on chilled water pipes?

Yes, but the foil facing must be maintained intact at all joints and fittings. For most chilled water applications, closed-cell elastomeric foam is simpler and more reliable. See: Foil-Faced vs Elastomeric Foam.

Related Guides

• Vapour Barriers for Pipe Insulation — Complete Guide
• BS5422 Explained — The Complete Guide
• What Thickness Pipe Insulation Do I Need?
• Armaflex vs K-Flex — Which Should You Choose?
• How to Prevent Condensation on Copper Pipes
• Pipe Insulation for Cold Water Systems
• Foil-Faced vs Elastomeric Foam — Which Should You Choose?
• Pipe Insulation for Swimming Pools
• How to Cut and Install Pipe Insulation
• Mineral Wool Pipe Insulation — Complete Guide
• Phenolic Foam Pipe Insulation — Complete Guide (Kooltherm)
• Pipe Insulation Glossary