WAREHOUSE AND DISTRIBUTION DUCT FABRICATION
Warehouse duct is defined by run length and mounting height rather than by specification complexity. The runs are long, the bays are high, the branch count per square foot is low, and most of the package is exposed rather than concealed above a ceiling. JMC fabricates that scope in galvanized steel from its Pascagoula, MS shop.
Long spiral runs and exposed installation change what matters in fabrication, and they change what a good delivery looks like.
Published August 5, 2026 · JMC Fabrication
A distribution center is a large volume with very few interior partitions, which means the duct runs a long way with relatively few branches. That inverts the usual commercial ratio. Instead of a moderate amount of trunk feeding many small branches, there is a lot of trunk and comparatively few fittings.
Spiral round is often the right answer for those runs. It is efficient on airflow, it installs quickly in long sections, and it looks acceptable exposed, which matters because warehouse duct is normally hung in the open at high bay rather than hidden. Rectangular still shows up at equipment connections, in office and support areas, and where the layout forces it.
Exposed installation also raises the bar on appearance and consistency. Duct that will be visible for the life of the building needs consistent seam presentation and clean joints, and dimensional variation across long runs shows in a way it does not above a ceiling grid.
Four scopes, often with different requirements:
- Main distribution runs: Long spiral round or rectangular trunk at high bay, fabricated in sections sized for practical handling and hoisting on site.
- Make-up air and ventilation: Supply and general exhaust sized for the air change rate the design carries, which in a large volume building can mean substantial duct for a modest branch count.
- Office and support areas: Conventional low-bay commercial duct for the office block, break areas, and restrooms, usually rectangular with a normal branch density.
- Process and specialty exhaust: Where the facility runs battery charging, packaging equipment, paint or coating operations, or other processes that call for dedicated exhaust, which may push into welded or heavier-gauge construction.
The differences are geometric more than regulatory:
| Attribute | Typical commercial | Warehouse and distribution |
|---|---|---|
| Run length | Moderate, many turns | Long, few turns |
| Fitting density | High per linear foot | Low per linear foot |
| Dominant profile | Rectangular | Spiral round for main runs |
| Installation | Concealed above ceiling | Exposed at high bay |
| Field constraint | Tight plenum coordination | Hoisting and access at height |
Long duct is awkward freight and awkward to handle at height. Section length is a real fabrication decision, balancing fewer joints in the run against what the crew can actually hoist and connect with the lift equipment they have on site.
JMC's project management asks that question at the front of the job rather than assuming a standard length. Sections get sized to the crew's equipment and access, then shipped in install order so the run assembles in sequence instead of the crew hunting for the next section in a pile.
Freight economics also work in favor of regional sourcing here. Duct is bulky and warehouse packages are duct-heavy, so shipping from Pascagoula rather than from out of state takes meaningful cost out of a Gulf Coast or Southeast project.
- Building footprint and clear height, which drive run length and mounting
- SMACNA pressure class and gauge from the mechanical specification
- Estimated linear footage by profile, spiral round versus rectangular
- Make-up air and exhaust requirements, including air change rate if specified
- Any process or specialty exhaust scope and what it serves
- Lift equipment and access available to the install crew, which sets section length
- Delivery location and site staging constraints
Does JMC fabricate duct for warehouse and distribution projects?
Yes, as part of its commercial duct work. Warehouse packages are usually galvanized SMACNA construction with a high proportion of long spiral round runs and a low fitting count relative to linear footage.
Why is spiral duct common in warehouses?
It is efficient on airflow, it installs fast in long sections, and it presents acceptably when hung exposed at high bay, which is how most warehouse duct is installed. Rectangular still appears at equipment connections and in office areas.
How long are the duct sections?
That is a project decision rather than a shop standard. Longer sections mean fewer joints in the run, but the crew has to be able to hoist and connect them with the equipment on site. JMC asks what lift equipment and access the crew has and sizes sections to it.
Does exposed duct change how it is fabricated?
It raises the bar on consistency. Seam presentation and joint cleanliness matter more when the duct is visible for the life of the building, and dimensional variation shows across long exposed runs in a way it does not above a ceiling.
Can JMC handle process exhaust inside a distribution facility?
Yes, and it usually prices as its own scope. Battery charging, packaging equipment, and coating operations can call for heavier gauge or welded construction rather than standard commercial detail, so flag that scope in the RFQ.