Why standards matter for the machine you buy
The HVAC duct standard your project complies with is not just a paperwork question. It dictates the gauge of sheet metal you cut, the seam type you form, the reinforcement spacing, the leakage rate at acceptance test and the tolerances your machine must hit. If the standard is specified after you have bought the duct line, retrofitting compliance is significantly more expensive than configuring it correctly up front.
This guide is a comparison to use when a project specification mentions a standard you are not familiar with, so you can specify the right machine, the right tooling and the right PLC recipe before the contract is signed.
SMACNA: North America, Middle East, international airports
SMACNA (Sheet Metal and Air Conditioning Contractors' National Association) publishes the dominant ductwork construction standard used in the United States, Canada, the Gulf region and on most international airport projects. The two key documents are HVAC Duct Construction Standards, Metal and Flexible (rectangular) and Round Industrial Duct Construction Standards (round and oval).
SMACNA defines pressure class in inches of water gauge (in.wg). Static pressure classes for rectangular duct are 1/2, 1, 2, 3, 4, 6 and 10 in.wg positive and 1/2, 1, 2 and 3 in.wg negative. Duct gauge, reinforcement type and joint type are tabulated against pressure class, the larger duct dimension and the reinforcement spacing, so the same 600 mm duct can need a different gauge at the same pressure depending on whether it is reinforced every 1.2 m or every 1.5 m. Read the exact case from the SMACNA tables.
Sealing is graded as Class A, B, C or unsealed. Class A is the tightest (joints, seams and penetrations all sealed) and is required for plenums, supply duct above the ceiling and most medium-pressure systems. Class B seals joints and seams only. Class C seals only transverse joints. The leakage limits are documented in our SMACNA Seal Class A, B, C explainer.
Acceptance testing is done by the SMACNA Duct Air Leakage Test method: the duct is pressurised to its design class, leakage is measured with a calibrated orifice plate, and the result is compared to the maximum allowable rate for the seal class in CFM per 100 ft² of duct surface area at the test pressure.
EN 1505 / EN 1506: Europe
EN 1505 is the European standard for sheet metal rectangular ductwork dimensions and tolerances. EN 1506 is the equivalent for circular ductwork. EN 1507 covers leakage testing for rectangular duct, and EN 12237 covers round duct leakage. Together these documents form the European duct construction framework, harmonised by CEN (European Committee for Standardisation) and adopted in EU member states plus Switzerland, Norway and the UK (alongside DW/144).
EN 1505 and EN 1506 themselves cover dimensions and tolerances. The pressure limits and air-tightness classes A, B, C and D come from EN 1507 (rectangular) and EN 12237 (circular): Class A for systems up to 500 Pa positive, Class B up to 1000 Pa, Class C up to 2000 Pa, with Class D as the tightest class for special applications. Note that European pressure classes are stated in pascals not inches of water gauge; the conversion is 1 in.wg ≈ 249 Pa, so SMACNA +2 in.wg ≈ 500 Pa, roughly matching EN Class A.
In the air-tightness classes, A is loosest and D is tightest. Each class allows a leakage of a constant times the test pressure to the power 0.65 (0.027, 0.009, 0.003 and 0.001 for A to D, giving litres per second per square metre of duct surface), a different unit and a different test method than SMACNA.
European practice states sheet thickness in millimetres (typically 0.5 to 1.2 mm), while SMACNA tables use galvanized sheet gauge numbers (26, 24, 22, 20, 18 ga), not American Wire Gauge, which is a wire standard. Reinforcement spacing and type at a given pressure class often differ by 100–300 mm from SMACNA.
AS/NZS 4254: Australia and New Zealand
AS 4254, often written AS/NZS 4254, is the standard for ductwork in Australia and is also used in New Zealand. Part 1 (AS 4254.1) covers flexible duct and Part 2 (AS 4254.2) covers rigid duct, including sheet metal duct. The standard is called up by the National Construction Code (NCC) in Australia and the Building Code in New Zealand, and is referenced in most large commercial and industrial HVAC project specifications.
Like the European documents, AS 4254.2 states pressure in pascals and sheet thickness in millimetres. Its leakage requirements are set in its own terms, so do not assume an EN 1507 class carries over one to one. The reinforcement and tolerance tables are calibrated to local Australian construction practice, with specific clauses on seismic restraint and fire-rated penetrations that reflect Australian Building Code requirements.
AS 4254.2 classifies rigid duct by static pressure in pascals, with gauge, joint and sealing requirements rising with the pressure class. Most Australian commercial supply and return systems sit in the lower classes; data centre, cleanroom and high-velocity systems are specified in the higher ones.
DW/144: United Kingdom
DW/144 is the UK specification for sheet metal ductwork, published by BESA (the Building Engineering Services Association, formerly HVCA). DW/144 is the dominant fabrication specification on UK construction projects and is referenced in most UK Mechanical and Electrical specifications.
DW/144 broadly aligns with EN 1505 but adds UK-specific clauses on installation tolerance, joint sealing material specifications, fire-rated duct construction and acceptance testing procedure. It covers low pressure (up to 500 Pa), medium pressure (up to 1000 Pa) and high pressure (up to 2000 Pa) ductwork, with air leakage limits aligned to the EN air-tightness classes A, B and C. Leakage testing is mandatory for high-pressure ductwork and is required for low and medium pressure only when the job specification calls for it.
For global fabricators bidding into UK projects, DW/144 compliance is normally a contractual requirement and the specification document is mandatory reading. Many UK consultants specify DW/144 by reference and then audit the fabricator's quality control records against the document during the project.
Side-by-side comparison table
The table below summarises the key differences across the four major standards. Use it as a quick reference; always consult the source document for binding clauses on a specific project.
- Pressure class units: SMACNA uses in.wg. EN 1505, AS/NZS 4254 and DW/144 use Pa.
- Gauge units: SMACNA uses galvanized sheet gauge numbers. EN, AS/NZS and DW/144 use millimetre thickness.
- Joint types: SMACNA permits TDF, slip-on flange, drive cleat and angle flange. EN 1505 permits flanged joints, slip joints and welded joints. AS/NZS 4254 broadly aligns with EN 1505. DW/144 specifies flanged joints with detailed gasket material requirements.
- Sealing and leakage: SMACNA seal classes (A, B, C) say which joints and seams get sealed; its leakage classes (CL) set the allowed leakage. EN and DW/144 classes A to D are leakage classes. Compare leakage class with leakage class, not seal class with leakage class, and check the source documents for project compliance.
- Reinforcement spacing: All four specify reinforcement intervals based on duct dimension and pressure class, but the actual spacing values differ by 100–300 mm at any given operating point.
- Leakage test method: SMACNA uses CFM/100 ft² at test pressure. EN, AS/NZS and DW/144 use l/s per m² of duct surface at test pressure. Conversion is non-linear because of the different reference units.
- Geographic scope: SMACNA in USA, Canada, GCC, international airports. EN 1505 in EU + Switzerland + Norway. AS/NZS 4254 in Australia + New Zealand. DW/144 in UK + Ireland.
How to specify the right standard for your project
If you are a building owner, consultant or contractor planning an HVAC project, the standard is normally inherited from the project specification: your M&E consultant or the project owner specifies it in the design package. Before procuring duct or duct-making machinery, confirm which standard is binding by reading the M&E specification.
If you are a fabricator setting up a duct production line, your standard is determined by the markets you serve. North American or Gulf market fabricators should configure their line for SMACNA. European fabricators for EN 1505. Australian and New Zealand fabricators for AS/NZS 4254. UK fabricators for DW/144. Multi-region exporters benefit from a multi-standard PLC, which costs about 5–8% more than a single-standard line but eliminates retooling between project standards.
How Taokron machines comply
Tell Taokron the project standard on your enquiry (SMACNA, EN 1505, AS/NZS 4254 or DW/144) and the tooling, PLC recipes and seam types are configured to match. On a line set up this way, the operator selects the project standard at job start and the PLC adjusts seam selection, reinforcement spacing, gauge thresholds and tolerance bands. The first article from a multi-standard line should pass the project's acceptance test on day one.
The Factory Acceptance Test (FAT) can be written around the project standard. For SMACNA projects that could be a SMACNA leakage test against the specified leakage class (CL) at the design pressure; for EN 1505 an EN 1507 test at the test pressure of the specified class (for example Class B at 1000 Pa); for AS/NZS 4254 the AS 4254.2 test method; for DW/144 the DW/144 high-pressure leakage test. Agree the test method and acceptance criteria in the quotation, and confirm with your consultant that the test record will be accepted.
The flagship SBAL-V auto duct line and the SBTF series spiral tubeformers can be configured to suit any of the four standards. The TDF flange machine and the SBLC lockformer support SMACNA TDF, EN 1505 flanged joint and AS/NZS 4254 flange profiles via tooling change-out. See SBAL-V product page and TDF flange machine for technical details.
When standards conflict: which wins?
Occasionally a project specification references multiple standards (for example, a Saudi airport project specifying SMACNA and a separate EU consultant adding an EN 1505 clause). The contract document hierarchy normally resolves this (the prime contract specification overrides any subsidiary documents), but the practical answer is to fabricate to the tighter of the two standards. The tighter spec passes both tests; the looser spec fails the tighter test.
For leakage: if your contract specifies both a SMACNA leakage class and an EN 1507 class, convert both allowed rates to the same unit at the actual test pressure and fabricate to the lower one. Sealing to SMACNA Seal Class A is normally needed to get there, and the leakage test is what proves it.
Standards revisions to watch
The current SMACNA rectangular standard is the 4th edition (2020). EN 1505 dates from 1997 and EN 1507 from 2006. AS 4254.1 was revised in 2021, while AS 4254.2 is the 2012 edition and is listed as pending revision. DW/144 was last revised in 2013. Check the edition named in your specification before you quote.
For projects that span standard revisions (e.g. a 3-year build project in Australia that runs into a new AS 4254.2 edition), confirm in the contract which version of the standard applies: the version current at contract signing, or the version current at first-article inspection. This is normally a project specification clause; if it is silent, default to the version current at first-article inspection.
Get a Taokron quote configured for your project standard →
FAQ
What is the difference between SMACNA and EN 1505?
SMACNA is the North American standard with pressure classes in in.wg and seal classes A/B/C. EN 1505 is the European standard for rectangular duct dimensions, used with EN 1507, which sets air-tightness classes A/B/C/D and pressure limits in Pa. They overlap functionally but are not interchangeable: gauge tables, reinforcement spacing and sealing requirements differ on every duct size.
Which standard applies in the Middle East?
SMACNA dominates the Gulf region (Saudi Arabia, UAE, Qatar, Kuwait, Bahrain, Oman) because most major projects are specified by US or UK consultants. EN 1505 appears occasionally on European-led projects.
Which standard applies in Australia and New Zealand?
AS 4254.1 (flexible duct) and AS 4254.2 (rigid duct) are called up by the National Construction Code in Australia and are also used in New Zealand. Taokron configures SBAL-V and SBAL-III lines to AS/NZS 4254 on request.
Can one auto duct line meet multiple standards?
Yes. Name the standard on your enquiry and Taokron configures the SBAL-V PLC recipes, tooling and seam types to match SMACNA, EN 1505, AS/NZS 4254 or DW/144. The operator selects the standard at job start; the line adjusts seam type, reinforcement spacing and tolerance bands.
What is DW/144 and where is it used?
DW/144 is the UK specification for sheet metal ductwork, published by BESA. It is used across the UK and parts of Ireland and on UK-led projects globally. It covers low, medium and high pressure ductwork (up to 2000 Pa) and broadly aligns with EN 1505 with UK-specific clauses on installation tolerance and acceptance testing.
