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Insulation thicknesses – pipework, ductwork

1. LTHW Heating, Condenser Cooling Water, Dry Cooler Circuits (up to 85°C)

THICKNESS BASED ON BS5422 TABLES 12 & 13
NOMINAL PIPE SIZE (mm) MINERAL WOOL THICKNESS (mm)
15 25
20 25
25 25
32 30
40 30
50 30
65 30
80 30
100 30
125 40
150 40
200 40
250 40
300 and above 40
flat surfaces 40

2. Domestic Hot Water Services

THICKNESS BASED ON BS5422 TABLES 15
NOMINAL PIPE SIZE (mm) MINERAL WOOL THICKNESS (mm)
15 25
20 30
25 30
32 30
40 30
50 30
65 40
80 40
100 40
125 40
150 40
flat surfaces 50

3. Internal Cold Water Services, Chilled Water Services and Fire Protection Services - Protection from Freezing, Including Cold Water Feeds and Vents

THICKNESS BASED ON BS5422 TABLES 12 & 13
NOMINAL PIPE SIZE (mm) MINERAL WOOL THICKNESS (mm) INDOORS (1 & 2)
15 60
20 50
25 30
32 30
40 30
50 30
65 30
80 30
100 25
125 25
150 25
200 25
250 25
300 and above 25
flat surfaces 25

• Indoor installations include roof spaces, ventilated ground floor voids and unheated basements etc.;

• Also includes hot services that operate intermittently located in spaces in (1) above.

The above thicknesses comply with or exceed the requirements of Byelaw 49 of the Water Supply Byelaws ad BS 6700 1987.

4. Internal Cold Water Services, Chilled Water Services and Rainwater Pipes to Prevent Condensation

THICKNESS BASED ON BS 5422 TABLE 7
NOMINAL PIPE MINERAL WOOL THICKNESS (mm)
SIZE (mm) 10OC* 5OC* 0OC*
15 20 25 30
20 20 25 30
25 20 30 40
32 20 30 40
40 20 30 40
50 25 30 40
65 25 30 40
80 25 30 40
100 30 40 50
125 30 40 50
150 30 50 60
200 30 50 60
250 40 50 60
300 40 50 60
flat surfaces 40 60 80

* Temperature and contents

10ºC – Cold water services

5ºC – Chilled water services

0ºC – Rainwater pipes

Cold water storage tanks, including feed and expansion tanks.

• All flat sided tanks – 50mm thick;

• All externally flanged tanks – 80mm thick applied in two layers, each 40mm thick.

5. Ductwork Carrying Warm Air

THICKNESS BASED ON BS 5422 TABLE 16
TEMPERATURE DIFFERENCE BETWEEN AIR IN DUCT AND AMBIENT STILL AIR MINERAL WOOL THICKNESS (mm)
+10K 40
+25K 50
+20K 60

6. Ductwork Carrying Chilled Air (Condensation Control)

THICKNESS BASED ON BS 5422 TABLE 17
MINIMUM AIR TEMPERATURE INSIDE DUCT MINERAL WOOL THICKNESS (mm)
150C – 200C 25
100C – 140C 40
50C – 90C 60
00C – 40C 70

7. Refrigeration Pipework for Condensation Control

APPLICATION REFRIGERANT
PIPE O/D
ARMAFLEX INSULATION THICKNESS (mm) THICKNESS BASED ON BS 5422 TABLE 2 FO
NORMAL CONDITIONS.
MILD CONDITIONS AMBIENT 20ºC   R.H 60% NORMAL CONDITIONS AMBIENT 20ºC R.H 70%* SERVE CONDITIONS AMBIENT 25ºC R.H 80%
Down to minus 18ºC 15 to 114mm 19 19 32
 Above 114mm and other flat sheet applications 19 19 25 45
Down to -30oC 15 to 114mm 19 32 38
 Above 114mm and other flat sheet applications 19 19 32 64
Down to -40oC 15 to 114mm 25 32 49
 Above 114mm and other flat sheet applications 25 32 41 73

* Unless otherwise indicated, normal conditions are to be applied.

• Liquid refrigeration pipes external to buildings and subject to solar radiation shall have a reflective or light coloured finish applied to the “Armaflex” insulation.

At REMARS, we use industry standards, regulations to help measure effective insulation thicknesses of pipework / ductwork. Call us or send us email to help you properly size insulation thicknesses.

Get in touch…

we can help you get an accurate Insulation Thicknesses of ductwork / pipework for your next project.

REMARS Engineering Team
Written by REMARS Engineering Team
https://remars.co.uk
REMARS is a multidisciplinary MEP consulting team specialising in HVAC design, BIM integration, and complex engineering projects across commercial, industrial, and energy sectors.

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