Are you a homeowner or building manager?
Find a Contractor »

Duct-related Changes to IAPMO’s 2018 Uniform Mechanical Codes

Posted on:

In February 2018, the International Association of Plumbing and Mechanical Officials (IAPMO) began shipping the 2018 editions of the Uniform Mechanical Code and the Uniform Plumbing Code. To purchase these codes, go to

The 2018 editions represent a 3-year code cycle which involved code committees taking action on submitted proposals and considering comments from the public and affected parties. Below are some HVAC duct related revisions to the 2018 UMC that represent significant changes and/or issues.

  • (Revised) 601.2, Sizing Requirements, will require duct system sizing to be in accordance with ACCA Manual D listed in Table 1701.1, or by other approved methods. This change makes Manual D a mandatory requirement in the UMC, whereas previous editions had referenced Manual D in a non-mandatory Exhibit. This change was made possible due to ACCA updating Manual D to contain “normative” code-enforceable language as well as being designated as an ANSI “consensus-based” standard.
  • (Revised) 603.4.1, Length Limitation, will allow factory-made flexible air ducts and connectors to be used as an elbow at a terminal device, as long as they are limited to 5 feet in length. This clarifies the existing requirement that prohibits their use in commercial buildings in lieu of rigid elbows or fittings. The exception for residential occupancies is still in effect (despite efforts to delete it during the code change cycle); hence, residential buildings can continue to use flex ducts in lengths greater than 5 feet.
  • (New) 603.10.1, Duct Leakage Tests, will require ductwork to be leak-tested per a SMACNA test manual. That manual is for duct systems having static pressures of 3” W.C. and higher. The test only involves representative sections totaling not less than 10% of the total installed duct area. However, if the tested 10% percent fails to comply, then 40% of the total must be tested. Failing that will require testing 100% of the total installed duct area.

IAPMO is currently seeking proposals to the UMC and the UPC that will culminate with the 2021 editions of those codes. The due date for proposals was March 16, 2018. On behalf of the ACCA Codes Committee, ACCA has submitted several proposals for the UMC, as shown below.

  • Revise 1105.1, Human Comfort, to require ACCA Manual J for calculating loads and ACCA Manual S for selecting cooling equipment. Manual J and S are currently referenced in non-mandatory Exhibit E in the UMC.
  • Revise 601.2, Sizing Requirements, to require zoned duct systems to comply with ACCA Manual Zr.
  • Revise 303.1, Listed Appliances, under 303.0, Installation, to require HVAC systems to comply with ACCA 5 QI as minimum criteria for proper installation.

Proposals for the UMC/UPC will be considered by the respective IAPMO Technical Committees during their May 15-18, 2018 meetings in Ontario, CA.

Industry Involvement Needed … Being Proactive for the Current Code Change Cycles!

The ICC “Group A” I-Codes three-year code change cycle has begun for what will be the 2021 editions of the IMC, IRC, IFGC, IPC and others. ACCA has submitted several proposals to revise the 2018 IMC and IRC (mechanical). The proposals have been published on the ICC’s webpage and will be considered by the applicable ICC committees in mid-April at hearings in Columbus, Ohio. Click here to access all I-Code proposals for “Group A”:

In addition, the IAPMO three-year code change cycle has begun for the UMC and UPC codes, which will culminate in the 2021 editions. ACCA has also submitted proposals for the UMC, which will be considered by the IAPMO UMC Technical Committee at its meeting in mid-April in Ontario, CA.

The ACCA Codes Committee takes a proactive role in developing proposed code changes based on member input, including commenting on other proposed code changes. For the above 2021 code change cycles, the Codes Committee is SEEKING CONTRACTOR INPUT on the above proposals. Contractors are encouraged to review the above code change proposals when they become available and send your input on them to

Persons interested in becoming more involved on the ACCA Codes Committee or learning more about the codes process should contact

David Bixby

Posted In: Technical Tips

Looking for an ACCA QA Accredited Contractor?

Are you a homeowner or building manager?


join now

PLUS It's Risk Free!