Why Our Fiberglass Reinforced Plastic UnderDuct is Superior


UnderDuct Double Wall and Single WallMonoxivent’s UnderDuct fiberglass HVAC ductwork provides excellent resistance to corrosion and leakage. The corrosion resistance qualities are maintained throughout both the inside diameter (ID) and outside diameter (OD) allowing for a wide range of applications.

Ease of Use

Monoxivent’s UnderDuct fiberglass duct can be directly placed onto a pea gravel bed in a graded trench, then backfilled with pea gravel eliminating concrete encasement. Simple joining methods provide for easy and quick installation, and the FRP duct is impervious to minerals or salts present in soil.


Monoxivent’s UnderDuct systems can be sealed to achieve a water and air tight system. A leak-free system and smooth interior surface will ensure the air reaches its destination efficiently and without contamination, when installed correctly.

Material Integrity

Monoxivent’s UnderDuct FRP fiberglass duct is filament wound with two chemically inert materials – glass and resin. The finished product provides longer underground service life than galvanized sheet metal, stainless steel, or PVC coated sheet metal. The filament winding provides greater hoop strength resulting in a stronger duct than other methods of construction such as hand lay-up. The finished product is lighter than steel while offering superior acoustical qualities and corrosion resistance.


Monoxivent’s UnderDuct has been tested by ICC-ES and listed (PMG-1171) and shown to be compliant with the following building codes: IMC, IRC, UMC, and CMC. Corrosion Composites adhere to ASTM, SMACNA, AWWA, and other industry standards.


Monoxivent’s UnderDuct FRP products are available in straight lengths, standard and custom fittings, or in shop fabricated sections. All Monoxivent FRP duct can be shipped in prefabricated assemblies. Pre-insulated double wall duct has many advantages, including assured uniformity of insulation, permanent protection of insulation, and all-in-one installation.

FRP Solutions Brochure

Monoxivent FRP Capability Statement

Wide Range of Products Provide Versatility

The right product for a wide variety of jobs and needs, including:

Flume Hoods
Tank Covers
Stack Liners
Pressure Vessels, and more!

UnderDuct Vs. The Competition

Underduct has distinct advantages over its competitors

UnderDuct by Monoxivent provides the most versatile and cost effective Underground Fiberglass Reinforced Plastic (FRP) Duct on the market. We provide a wide range of solutions for the most demanding environments to standard layouts.

Monoxivent’s manufacturing source has over 50 years of experience and is a leader in the Under-Slab Fiberglass Duct market. Monoxivent has a nationwide network of sales representatives and a top-tier inside support staff the provides: engineering, design, sales, service, and marketing. UnderDuct is offered in single wall and pre-insulated double wall construction to meet any ventilation needs. Monoxivent 824 Low Smoke Class 1 duct is approved for direct burial. UnderDuct has received Code Compliance Approval from ICC Evaluation Service.

UnderDuct markets for supply, return, and exhaust systems include, but are not limited to: auditoriums, auto exhaust, banks, botanical centers, churches, high rise office, hospitals, libraries, parking garages, residences, restaurants, schools, super markets, swimming pools, and zoos.