Modular Plenum System FAQ

A plenum is the structural enclosure that manages radiator discharge air from a standby generator. The industry uses many names, generator plenum, genset plenum, plenum tower, generator shroud, radiator shroud, discharge stack, discharge tower, discharge chimney, radiator discharge duct, and discharge ductwork. RoXteel's product is a standardized, modular, self-supported version of this infrastructure.

In the field the terms are often used interchangeably. A 'generator shroud' or 'radiator shroud' typically refers to a sheet-metal enclosure around the radiator discharge. A 'plenum' or 'plenum tower' implies a taller, structural enclosure that manages discharge air at height. RoXteel's Modular Plenum System is a structural, self-supported, modular tower, not a bolt-on sheet-metal shroud. It is engineered to IBC / ASCE 7 loading and divorced from the genset enclosure.

A divorced plenum is structurally independent from the genset enclosure. It supports itself, it does not transfer load to or rely on the genset package, the enclosure, or any surrounding screen wall. RoXteel's system is divorced by design: the plenum is self-supported, which simplifies scope, reduces coordination between trades, and makes the system repeatable across genset brands and project sites.

It is built in 20-foot modular sections, divorced from the genset enclosure (self-supported), and repeatable across projects, sites, and genset brands. It is not a custom plenum offering. Only a few interface components (flashing kits) are project-specific, the system itself is not.

The genset enclosure includes a radiator discharge bump-out that insets into the plenum. RoXteel uses angle flashing kits to seal the interface between the genset bump-out and the plenum opening. These flashing kits are among the few project-specific components, the plenum system itself is standardized.

40 ft (2 × 20 ft sections, 2 picks), 60 ft (3 × 20 ft sections, 3 picks), 80 ft (20 ft straddle base + 60 ft of plenum), and 100 ft (40 ft straddle base + 60 ft of plenum, designed to accommodate double-stacked gensets). 80 and 100 ft configurations with straddle structures are handled case by case. Every tower configuration is engineered to be self-supported.

Yes. The system is engineered to resist applicable IBC / ASCE 7 loading (wind, seismic, snow, ice, live load) with no support required from surrounding buildings or screen walls.

The optional turn vane redirects radiator discharge air upward into the plenum. It sits below the radiator opening and includes a lip intended to prevent water from feeding back toward the radiator. With the turn vane, drain holes move water to the concrete below. Whether you need one depends on your site airflow requirements, discuss it during the Solution Call.

The standard plenum bottom is open to concrete, no bar grating as standard. The tower sits slightly above concrete so water can drain. Optional weather protection includes a bird screen and a weather head. The optional turn vane includes drainage provisions. Angle flashing kits seal the genset-to-plenum interface.

The base cube weighs approximately 9,500 lb. Other cubes weigh approximately 8,800 lb. These weights are provided for rigging planning and crane selection, RoXteel supplies pick plans and rigging information for every project.

Two 20-foot sections per step-deck trailer load. The 20-foot sections are designed for efficient shipping without pilot cars. RoXteel is primarily the manufacturer, customers may arrange transportation. RoXteel supports delivery planning and JIT scheduling.

Approximately 10× faster erection, about 90% less erection time and 90% less subcontractor labor hours versus conventional site-built discharge infrastructure. The first tower normally takes a couple of days; as crews learn the system, later towers can often be erected in less than a day. Expected cadence is approximately 2–3 sixty-foot towers per week.

RoXteel does not install plenums directly. On Arizona projects, sister company ATM Steel can potentially provide installation depending on schedule alignment. Every project receives a comprehensive installation guide, pick plans, rigging information, weights, pick counts, a dedicated RoXteel project manager, first-install support, and ongoing installer question support.

Foundation reaction loads are available through the genset packager or project partner. When working directly for a general contractor, RoXteel can provide them to the engineer of record. Anchoring (anchor bolts or drill-and-epoxy) is installed by the client or installer, anchoring installation is not RoXteel's scope.

Optional exhaust can be included, preinstalled, flanged, and integrated with the plenum cube (supplied by a partner; RoXteel does not manufacture exhaust). With optional insulation, the wall assembly may reduce sound transmission from low-frequency sources by approximately 25 dB (not a guaranteed site result). RoXteel does not claim quantified backpressure reduction; the team believes the plenum should not adversely affect radiator fan backpressure, but supporting test data is not yet available.

SSPC-SP5 White Metal Blast preparation, Galvapac zinc primer, and a 2-component polysiloxane topcoat applied to externally exposed portions as applicable. Plenum components are zinc coated. This structural steel coating system may also be available for the industrial steel assembly offering.

Standard lead time is approximately 6 to 9 months across configurations. An inventory program is launching early 2027, standard 20-foot plenum sections supporting towers up to 60 feet, with approximately 4 to 6 weeks lead time ready for install. Straddle bases are not inventory products. Storage is available for a per-unit fee, and JIT delivery is available.

Current information indicates the RoXteel plenum does not affect genset warranties. Approval concerns may need review in unusual cases involving very oversized radiator openings (approximately wider than 12 feet).

The system is engineered to resist applicable IBC / ASCE 7 loading, wind, seismic, snow, ice, and live load. Drawings are PE stamped and licensed as needed by project. The framing is 100% HSS-free, using angles and beams. Modules connect at corners plus internal exhaust flanges with approximately 12 exterior bolts per cube.

Patent Pending, USA & International.