Armaflex Pipe Insulation Thickness Guide: Which Wall Thickness Do You Need?

Armaflex pipe insulation is available in four standard wall thicknesses — 9mm, 13mm, 19mm and 25mm — and choosing the right one for your application is critical for thermal performance, condensation control and compliance with Part L of the Building Regulations. This guide explains which wall thickness to use and why.

Why Wall Thickness Matters

The wall thickness of pipe insulation determines how much heat is lost or gained through the insulation. A thicker wall means lower heat loss on heating pipework and lower heat gain on chilled water and refrigeration pipework. For chilled water and cold pipework, wall thickness also determines whether the insulation can prevent condensation forming on the pipe surface — a critical factor in preventing water damage, mould growth and corrosion.

Choosing too thin a wall thickness will result in excessive heat loss, condensation problems and potential non-compliance with Building Regulations. Choosing too thick is rarely a problem but adds unnecessary cost and can make installation more difficult in tight spaces.

Armaflex Wall Thickness Options

9mm Wall Thickness

9mm wall Armaflex EVO is the thinnest standard option and is primarily used for condensation control on chilled water and cold pipework in air-conditioned or temperature-controlled spaces. It is not suitable as the primary thermal insulation for heating or hot water pipework and will not meet Part L requirements for most heating applications.

Use 9mm Armaflex for:

• Chilled water pipework in air-conditioned spaces where ambient conditions are controlled
• Cold water supply pipework in heated buildings where frost protection is not required
• Refrigeration suction lines in plant rooms with controlled ambient conditions
• Fan coil unit connections in commercial HVAC systems

Do not use 9mm Armaflex for:

• Heating or hot water pipework (insufficient thermal performance)
• Pipework in unheated spaces or exposed to outdoor conditions
• Chilled water in high humidity environments without additional vapour protection

13mm Wall Thickness

13mm wall Armaflex is the standard specification for domestic heating, hot water and cold water pipework in the UK. It meets Part L of the Building Regulations for most domestic heating and hot water applications and provides effective frost protection on cold water pipework in heated buildings.

Use 13mm Armaflex for:

• Domestic central heating flow and return pipework (15mm, 22mm, 28mm pipe)
• Domestic hot water supply and distribution pipework
• Cold water supply pipework in heated buildings
• Condensate pipework from boilers and heat pumps
• Underfloor heating manifold connections
• Light commercial heating and hot water in conditioned spaces

Part L compliance note: 13mm wall meets the minimum insulation thickness requirements of Approved Document L (Conservation of Fuel and Power) for most domestic heating and hot water pipework in heated spaces. Always check the current edition of Part L for your specific application.

19mm Wall Thickness

19mm wall Armaflex is the standard specification for commercial HVAC, chilled water and heating mains in commercial buildings. It provides significantly better thermal performance than 13mm and meets Part L requirements for commercial heating and hot water applications. For chilled water, 19mm provides effective condensation control in most commercial environments.

Use 19mm Armaflex for:

• Commercial heating mains and primary circuits (28mm, 35mm, 42mm, 54mm pipe)
• Commercial hot water distribution and calorifier connections
• Chilled water flow and return in commercial HVAC systems
• Air conditioning pipework in commercial buildings
• Heat pump primary circuits and buffer vessel connections
• Domestic heating pipework in unheated spaces (lofts, garages, underfloor voids)

Part L compliance note: 19mm wall meets Part L requirements for commercial heating mains and hot water distribution in most commercial building applications. For pipework in unheated spaces, 19mm is typically the minimum specification.

25mm Wall Thickness

25mm wall Armaflex provides the highest thermal performance in the standard range and is specified for chilled water mains, refrigeration pipework, pipework in unheated or outdoor locations, and commercial applications where maximum energy efficiency is required. It is also the standard specification for pipework subject to CIBSE Guide C or NHS HTM requirements.

Use 25mm Armaflex for:

• Chilled water mains in large commercial HVAC systems
• Refrigeration suction and liquid lines in commercial refrigeration
• Pipework in unheated spaces, plant rooms and roof-level installations
• District heating secondary connections and heat network pipework
• Pipework subject to CIBSE Guide C, NHS HTM or other enhanced specifications
• Any application where maximum condensation control is required

Quick Reference: Armaflex Wall Thickness by Application

Armaflex EVO vs Self-Seal: Does Wall Thickness Affect the Choice?

Wall thickness is independent of whether you choose standard slit or self-seal Armaflex. Both are available in 9mm, 13mm, 19mm and 25mm wall thicknesses. Self-seal Armaflex has a factory-applied adhesive closure strip that speeds up installation — particularly useful on long straight runs — but provides identical thermal performance to standard slit Armaflex of the same wall thickness.

Specialist Armaflex Products and Wall Thickness

For applications outside the standard temperature range or with specific fire safety requirements, Armacell offers specialist products:

• Armaflex HT Solar — for solar thermal and high-temperature applications up to +150°C. Available in 13mm, 19mm and 25mm wall
• Armaflex Ultima — low smoke, halogen-free, Euroclass B-s1,d0. Available in 13mm, 19mm and 25mm wall
• NH Armaflex Smart — ammonia refrigeration. Available in 13mm, 19mm and 25mm wall

Need Help Choosing?

If you're unsure which wall thickness is right for your project, our technical team can help. Call us on 0161 775 1190 (Mon–Fri 8am–4pm) or browse our full range of Armaflex pipe insulation by pipe size and wall thickness.

Shop Armaflex by Wall Thickness

9mm & 13mm Wall Armaflex | 19mm Wall Armaflex | 25mm Wall Armaflex