Heating andVentilating

Contractors’Association

DW/144

Specification for

SheetMetalDuctwork

DW/144Specification for

Sheet Metal Ductwork

Low, medium and highpressure/velocity air systems

1998

Copyright © 1998 by theHeating and VentilatingContractors’ Association

All rights reserved

ISBN 0-903783-27-4

Further copies of this publication are available from:

Publications UnitHeating and Ventilating Contractors’ Association

Old Mansion House Eamont BridgePenrith Cumbria CA10 2BX

Tel: 01768 860405 Fax: 01768 860401e-mail: hvcapublications@welplan.co.uk

For more than a decade-and-a-half, the DW/142 Specification for Sheet MetalDuctwork published by the Heating and Ventilating Contractors’ Associationhas gained national and international recognition as the industry standard

against which the quality of ductwork manufacture and installation can be judged.In recent years, however, it has become increasingly evident to the members of

the HVCA Ductwork Group that the developments in technology and workingpractices which have taken place since the drafting of DW/142 have rendered obsolete significant parts of the document.

It was an acknowledgement of this state of affairs which led the Technical Sub-Committee of the Ductwork Group, ably chaired by Edgar Poppleton, to undertakethe task of producing a radically revised specification which would promote bestpractice and quality standards well into the next Millennium.

This new publication — designated DW/144 — represents the direct result ofthat initiative.

The new specification recognises the computer age — with special reference toCAD/CAM procedures and techniques — and the international performance stan-dards established by the Committee for European Normalisation (CEN), as well asthe need to update and consolidate much of the information contained in the origi-nal DW/142 publication and its Addendum A companion volume.

During the drafting process, the Technical Sub-Committee has consulted widelywith individuals and organisations throughout the building services and construc-tion sectors in order to ensure that the new specification fully reflected the currentthe “state-of-the-art” in terms both of technical expertise and industry best practice.

I firmly believe that this process has resulted in a publication which clearlydemonstrates the high level of professionalism which exists within the ductworkcommunity — and I take this opportunity of thanking all those who have con-tributed to its production.

In particular, my thanks go to Edgar Poppleton and his colleagues on theTechnical Sub-Committee, to Keith Elphick for the provision of invaluable techni-cal consultancy, and to Ductwork Group secretary Gareth Keller for overseeing theproject as a whole.

THE INDUSTRYSTANDARD

Ken ParslowChairman

Executive CommitteeDuctwork Group

1996-98

3

5

Like most industries, the ductwork sectormust be prepared continually to innovate inorder to survive and prosper.

A key element in that innovation process is thetimely review and updating of quality standards toensure that they continue to offer realistic bench-marks to which all professional individuals andorganisations can perform.

The development of this new Specification forSheet Metal Ductwork — designated DW/144 —has been carried out with that objective in mind.

In the 16 years since the publication of itspredecessor, DW/142 — and in the ten years sincethe supplementary volume Addendum A appeared— many technical advances, changes in workingpractices and regulatory introductions and amend-ments have taken place.

The common performance standards for duct-work being developed by the Committee forEuropean Normalisation (CEN), for example, hadto be taken fully into account during the draftingprocess. Similarly, notice had to be given to theprovisions of the Control of Substances Hazardousto Health (COSHH) and Construction (Design andManagement) Regulations, neither of which hadbeen issued when DW/142 was published.

It is not possible — nor, I think, desirable — toinclude in this foreword an exhaustive catalogue ofthe points of difference between this specificationand its predecessor. These will clearly emergefrom a detailed reading of the text.

I should, however, like to take the opportunity tohighlight a few topics which I believe to be of par-ticular significance. They are:● the omission of high-pressure Class D (in order

to conform to European practice);● the highlighting of information to be provided by

the designer;● the end-sealing of ducts and explosion risks;● the removal of standard sizes of rectangular

ducts;● the omission of cleated joints;● the acceptance of proprietary flanges certificated

to DW/TM1 no longer illustrated in detail;● the consolidation into the document of coverage

of hangers and supports;● the addition of a note on linings, along with their

cleaning considerations;● the consolidated graphical representation of

Class A, B and C air leakage characteristics,mandatory testing Class C only;

● updated appendices on galvanising after man-ufacture, stainless steel, pre-coated steel, alu-minium, Eurovent and galvanised material, plusa bibliography;

● transport, handling, storage and interface withDW/TM2 Guide to Good Practice — InternalCleanliness of New Ductwork Installations;

● an overview of fire-rated ductwork;● a new appendix on inspection, servicing and

cleaning access openings (the default inclusionof Level 1 should be noted);

● a new section on standard component drawings— incorporating a framework of nomenclature,and a description of drawing symbols, abbrevia-tions and rules — which is intended to reduceambiguity and promote common understanding;

● a rewritten description of all forms of dampers,for which I am indebted to Bill Clark and JohnMawdsley of the HEVAC Association.I take this opportunity to acknowledge the per-

mission granted by the Sheet Metal and AirConditioning Contractors’ National Association(SMACNA) of the USA for the use of its tie rodspecification (designer approval required).

And I also include a plea on behalf of ductworkconstructors to be allowed to make the final choiceof components and techniques within the parame-ters set by the designer, and allowed within thisspecification to satisfy performance characteristics.

It will, of course, be clear to anyone who hasever taken on such a task that the production of thisspecification has involved a colossal input in termsof industry consultation and from a wide variety ofindividuals, a number of whom I should like toidentify for special mention.

They are: former Technical Sub-Committeemembers Keith Waldron and the late Keith Angood;current members Chris Collins, Stuart Howard,Brian James and — last but by no means least —Jim Murray; technical consultant Keith Elphick; andDuctwork Group secretary Gareth Keller.

Finally, may I remind readers of the crucialimportance of ensuring that all ductwork is manu-factured and installed in a manner which is safe,efficient, effective and free of risk.

The publication of DW/144 is intended to assistsignificantly in the achievement of this objective.

MAINTAINING QUALITY

Edgar PoppletonChairmanTechnical

Sub-CommitteeDuctwork Group

Acknowledgements

The HVCA wishes to record its sincere thanks to the followingmembers — past and present — of the Technical Sub-Committeeof the Ductwork Group, who contributed their time, knowledge

and experience to the production of this document

Edgar Poppleton (chairman)

Keith Angood

Chris Collins

Stuart Howard

Brian James

Jim Murray

Keith Waldron

Technical Consultant:

Keith Elphick

Ductwork Group Secretary:

Gareth Keller

6

Other Ductwork-Related Publications

DW/143 A Practical Guide to Ductwork Leakage TestingDW/151 Specification for Plastic DuctworkDW/171 Guide to Good Practice for Kitchen Ventilation SystemsDW/191 Guide to Good Practice: Glass Fibre DuctworkDW/TM1 Acceptance Scheme for New Products: Rectangular Cross Joint ClassificationDW/TM2 Guide to Good Practice: Internal Cleanliness of New Ductwork InstallationsDW/TM3 Guide to Good Practice for the Design for the Installation of Fire and Smoke DampersTR/17 Guide to Good Practice: Cleanliness of Ventilation Systems

Copies of the above publications are available from:

Publications UnitHeating and Ventilating Contractors’ Association

Old Mansion House Eamont BridgePenrith Cumbria CA10 2BX

Tel: 01768 860405 Fax: 01768 860401e-mail: hvcapublications@welplan.co.uk

Previous Sheet Metal Ductwork Specifications_ Ductwork Specification for High-Velocity Air Systems (Circular) 1963 _ Standard Range of Rectangular Ducting 1967

DW/131 Sheet Metal Ductwork Specification for High-Velocity AirSystems (Rectangular) 1968

DW/121 Specification for Sheet Metal Ductwork (Low-VelocityLow-Pressure Air Systems) (Rectangular and Circular) — Metric 1969

DW/122B Specification for Sheet Metal Ductwork (Low-VelocityLow-Pressure Air Systems (Rectangular and Circular) — British 1969

DW/112 Standard Range of Rectangular Ducts and Fittings — Metric andBritish Units 1970

DW/132 Specification for Sheet Metal Ductwork (High-VelocityHigh-Pressure Air Systems) (Rectangular, Circular and Flat Oval) — Metric 1970

DW/141 Specification for Sheet Metal Ductwork (Low and High-Velocity/Pressure Air Systems) (Rectangular, Circular and Flat Oval)— Metric 1977

DW/142 Specification for Sheet Metal Ductwork (Low, Medium and HighPressure/Velocity Air Systems) 1982

DW/142 Specification for Sheet Metal Ductwork Addendum A (Low,Medium and High Pressure/Velocity Air Systems) 1988

7

Page

Notes 10

Part One - Technical Information to be provided by the designer1. Introduction 112. Standards 113. Components 114. Particular Requirements 11

Part Two - Standards5. Application 136. Ductwork Classification and Air Leakage 137. Materials 138. Ductwork Construction and Joint Sealing 14

Part Three - Rectangular Ducts9. Rectangular Duct Sizes 1510. Construction 15

10.1 General 1510.2 Steel Thicknesses 1510.3 Longitudinal Seams 1510.4 Cross Joints 1510.5 Stiffeners 1510.6 Ductwork Galvanised After

Manufacture 1610.7 Fastenings 16

11. Fittings 1611.1 Standardisation of Fittings 1611.2 Stiffeners 1611.3 Splitters 1611.4 Turning Vanes 1611.5 Branches 1611.6 Change Shapes 1611.7 Expansions and Contractions 1711.8 Sealant 17

Part Four - Circular Ducts12. Standard Sizes 2713. Construction 27

13.1 Longitudinal Seams 2713.2 Cross Joints 2713.3 Fastenings 27

14. Fittings 2914.1 Standardisation of Fittings 2914.2 Nominal Diameters 2914.3 Sheet Thickness 2914.4 Sealing of Joints 29

Part Five - Flat Oval Ducts15. Standard Sizes and Sheet Thicknesses 3516. Construction (Spirally wound) 35

16.1 General 3516.2 Longitudinal Seams 3516.3 Cross Joints 35

16.4 Fastenings 3516.5 Stiffening 35

17. Construction (Straight Seamed) 3518. Fittings 35

18.1 General Construction Requirements 3518.2 Standardisation of fittings 35

Part Six - Hangers and Supports19. General 43

Part Seven - General20. Access/Inspection Openings 4721. Regulating Dampers 4822. Fire Dampers 4923. Smoke Dampers 5024. Combination Smoke and Fire Dampers 5125. Flexible Ducts 5126. Flexible Joint/Connections 5227. Protective Finishes 5328. Connections to Building Openings 5329. Internal Duct Linings 5430. Thermal Insulation 5431. Kitchen Ventilation 5432. Fire Rated Ductwork 5433. Standard Component Drawings

and Abbreviations 54

Part Eight - AppendicesAppendix A. Air Leakage from

Ductwork 75Appendix B. Identification of

Ductwork 80Appendix C. Guidance Notes for the

Transport, Handling and Storage of Ductwork 82

Appendix D. Ductwork Systems andFire Hazards 83

Appendix E. Hot Dip Galvanizing afterManufacture 85

Appendix F. Stainless Steel for Ductwork 86Appendix G. Pre-Coated Steel 89Appendix H. Aluminium Ductwork 90Appendix J. Eurovent 91Appendix K. Summary of BS.EN10142:

1991 Continuously Hot-DipZinc Coated Mild Steel Stripand Sheet for Cold Forming 92

Appendix L. ‘Design Notes for Ductwork’(CIBSE Technical Memorandum No. 8) 93

Appendix M. Guidance Notes For Inspection,Servicing and Cleaning AccessOpenings 94

Appendix N. Bibliography 95Appendix P. Conversion Tables 97

8

Contents

List of TablesTable Page

Part Two - Standards1. Ductwork Classification and Air

Leakage Limits 13

Part Three - Rectangular Ducts2. Constructional Requirements

Low Pressure up to 500Pa 183. Constructional Requirements

Medium Pressure up to 1000Pa 194. Constructional Requirements

High Pressure up to 2000Pa 195. Fastening Centres 24

Part Four - Circular Ducts6. Standard Sizes 277. Spirally-Wound Ducts 288. Straight-Seamed Ducts 289. Permitted fastenings and maximum

spacings 2910. Fittings Sheet Thicknesses 29

Part Five - Flat Oval Ducts11. Standard sizes and sheet thicknesses 3612. Stiffening requirements

low and medium pressures 3713. Stiffening requirements

high pressure 3814. Permitted fastenings and maximum

spacings 40

Part Six - Hangers and Supports15. Supports for horizontal ducts - rectangular,

flat oval and circular 44

Part Seven - General16. Standard Abbreviations 72-73

Part Eight - Appendices17. Air Leakage Rates 7618. Recommended duct identification colours 8019. Examples of further identification symbols 8120. Ductwork galvanized after manufacture -

rectangular 8521. Compositions of the commonly used

Stainless Steel grades 8822. Rectangular aluminium ducts -

low pressure constructional requirements 9023. Circular aluminium ducts -

low pressure constructional requirements 9124. Zinc coating mass (weight) 9325. Access requirements for inspection,

servicing and cleaning 94

List of IllustrationsFigs Pages

Part Three - Rectangular Ducts1-8 Longitudinal Seams 209 Illustrations of panel stiffening 2010-12 Flanged cross joints 21

13-17 Socket and spigot cross joints 2218-24 Stiffeners 2325-28 Tie rod assembly 2429 Hard and Easy bends 2530 Turning Vanes 25

Part Four - Circular Ducts31 Spiral and straight seams 2932-38 Cross joints spirally wound ducts 30-3139-45 Cross joints straight seamed ducts 32-33

Part Five - Flat Oval Ducts53-58 Cross joints spirally wound ducts 39-4059-63 Cross joints straight seamed ducts 41-42

Part Six - Hangers and Supports64-75 Horizontal ducts

bearers and hangers 45-4676-77 Vertical ducts supports 46

Part Seven - General78-79 Fire barrier/fire damper expansion 5080 Flexible joint connections 5281-124 Standard component drawings -

Rectangular 55-61125-152 Standard component drawings -

Circular 62-67153-167 Standard component drawings -

Flat Oval 68-70168-177 Plant/equipment/miscellaneous 71

Part Eight - Appendices178 Permitted leakage at various

pressures 78179 Example of duct identification symbol 81

9