Frequently Asked Questions
How are Thermaduct products different than what I use now?
Thermaduct products are fully engineered high R-value, low air leakage pre-insulated duct solutions that offer high efficiency air distribution. Each duct system has a fiber free insulation core for increased indoor air quality. Air passes through a smooth aluminum interior, free from fibers that are found in duct liners. Because our products are pre-manufactured, your customer is assured the highest performance and energy savings available.
How is installing a Thermaduct product different than Sheet Metal?
While we try to keep our products familiar to HVAC contractors, there are some differences in using our phenolic products that should be observed. Support practices, connections and field modification all may differ in order to set the foundation for a long lasting, weather resistant application.
Online training is available for installers that covers the guidelines discussed in our installation manual. Contractors installing a Thermaduct product should talk to their local Thermaduct representative or request access directly on our training site.
Is Thermaduct your company or product?
Our Rectangular Outdoor Ductwork, Thermaduct, was our first pre-insulated solution we introduced in 2011 and bears our company name. We have gone on to develop round and flat oval solutions for both indoor and outdoor applications since then and have introduced them into the Thermaduct family of products.
What insulation R values can your products provide?
Our rectangular outdoor pre-insulated ductwork, Thermaduct, can provide R8 through R-24 insulated values. Thermaround comes standard at an R-12 insulated value. For indoor applications, both InspiralR and Floval made with R-6 phenolic panels.
Is cladding applied in the field with your outdoor products?
No, Thermaduct outdoor systems do not require cladding to be applied in the field. Whether you select our UV-stable 1000-micron vinyl cladding or our durable metal cladding options, the exterior finish on the product comes from the factory during fabrication. This ensures a consistent, high-quality weather barrier without additional field-applied cladding steps.
By eliminating the need for field-applied tapes or wraps, we avoid the common issues found in some other pre-insulated duct systems, where cladding tapes can degrade over time or be prone to misapplication. Our process provides a long-lasting, seamless protective surface that helps maintain insulation performance and appearance for years to come.
What are the lead times on ordering a Thermaduct product?
Thermaduct products are fabricated in licensed facilities across the country through trained fabrication partners. Lead times may vary from location to location, but standard lead times are usually 2-4 weeks from issuance of a PO and verified field measurements.
Are Thermaduct products easy to install?
HVAC Contractors should feel right at home installing Thermaduct products. Please review our Installation Resources Page for an overview of our systems installation steps. You can also receive a Contractor’s Installation Manual from any Thermaduct Representative.
Where can I buy Thermaduct products?
We have a network of partners in all major market areas across the United States. Locate your Representative here. If you do not see one in your area, please contact Thermaduct at 855-809-6903.
Can Thermaduct products be painted?
Vinyl cladded Thermaduct & Thermaround are not paintable. The three vinyl color options are specifically chosen and tested to ensure minimal heat absorption & buildup to maintain surface temperatures below expansion of vinyl. Paints can damage the cladding and would void Thermaduct’s 10 Year limited warranty.
For applications that require a specific architectural look, we would recommend our Architectural line of products that can offer 24 Kynar coated colors or paint grip galvanized metal.
Will Thermaduct products comply with the SMACNA Phenolic Duct Construction Standards?
Thermaduct rectangular products will meet or exceed the SMACNA Phenolic Duct Construction Standards, which are internationally recognized by the leading authority in HVAC construction. These do not currently apply to round or flat oval ductwork, but the same attention to product safety and longevity will be adhered to in all Thermaduct offerings.
Can your outdoor products be used indoors?
Thermaduct and Thermaround are designed to withstand the outdoor elements with unmatched quality and durability. For indoor applications, factory made air ducts benefit from a UL 181 listing, which does not extend to our vinyl cladded products. Both InspiralR and Floval are UL 181 listed products and are excellent solutions for indoor applications.
Where is Thermaduct Manufactured?
Thermaduct is headquartered in Perrysburg, Ohio.
Is there any required training to install Thermaduct products?
Thermaduct, Thermaround, InspiralR and Floval are designed to be familiar to HVAC Contractors. Despite this, we do require online training for installations to cover the differences in installing a phenolic system compared to traditional metal ductwork. Our installation instructions in our online courses respect your time and contain all documents in one place. You can request access today by visiting training.thermaduct.com.
What type of foam is Thermaduct using?
Thermaduct, Thermaround, InspiralR and Floval all use a high-quality phenolic insulation core with greater than 90% closed-cell content. This provides excellent resistance to water intrusion and the highest R-value per inch of any rigid insulation. For outdoor systems, this core is factory finished with either our UV-stable 1000-micron vinyl cladding or our durable metal cladding, giving you long-lasting protection and design flexibility without sacrificing thermal performance.
What Static Pressure can Thermaduct products handle?
Thermaduct products all have a high static pressure design. Proper reinforcement will be required.
Thermaduct - 10" w.c. Positive, 10" w.c. Negative
Thermaround - 10" w.c. Positive, 8" w.c. Negative
InspiralR - 10" w.c. Positive, 8" w.c. Negative
Floval - 10" w.c. Positive, 8" w.c. Negative
How do you accommodate dynamic load with your outdoor products?
Outdoor applications require additional considerations that may not be experienced in the indoors. Wind, rain and snow all need to be planned for. This is important with pre-insulated ductwork where snow doesn’t melt from escaping heat that may occur in a sheet metal installation that is not well insulated.
Thermaduct uses a patented reinforcement system called Airtruss™ to go above and beyond the SMACNA Phenolic Duct Construction Standards. Snow load calculations for each region across the country are considered in the design of our outdoor products. This system is built in, flange to flange, and gives our product a backbone that other pre-insulated duct systems do not have.
Why are your outdoor products white?
The standard color of our outdoor products is white to comply with Cool Roof Initiatives across the country. At peak temperatures a white roof is 20 degrees cooler than a roof with an aluminum coating, and up to 60 degrees cooler than a dark roof. This is important with ductwork as the temperature differences between your airstream and outdoor environment may be drastically different.
For installations where color may be important, our rectangular outdoor duct does have a tan and light gray color to match common building facades or with our Thermaround system, we offer a Kynar Finished Metal cladded system for architectural applications.
How are the seams of Thermaduct and Thermaround made?
While other manufacturers use tapes, adhesives and seams held together with screws, which experience degradation over time, our outdoor products use a patented heat or solvent welded seam to ensure impervious water and air integrity.
How do Thermaduct and Thermaround perform in warmer climates? Cooler climates?
Our outdoor products have a UV stable, 1000 micron vinyl cladding and are designed to handle any climate.
Do InspiralR and Floval come in other colors?
While Thermaduct and Thermaround’s cladding color has been carefully selected and is not paintable, both InspiralR and Floval can be painted in indoor exposed applications. These paints should be water based and compatible with aluminum surfaces.
Consult your application’s engineer when painting InspiralR and Floval as paint selections do have a bearing on fire performance requirements.
Can I download your guide specification?
Thermaduct products guide specifications can be found on our literature page or on SpecLink Cloud in the Division 23 master spec.
How is acoustic performance handled?
Thermaduct systems provide a smooth, rigid phenolic construction that helps eliminate many common noise issues found in traditional metal ductwork. While phenolic insulation does not absorb sound the way fibrous duct liners do, it reduces noise in other ways:
- Vibration Control – The rigid phenolic core and cladding minimize “oil canning” or vibration resonance that can occur with sheet metal.
- Thermal & Pressure Stability – Low air leakage and tight gasketed connections reduce whistling and rattling at joints.
For projects with strict sound attenuation requirements, Thermaduct ducts can be paired with inline silencers or acoustically liners to achieve targeted noise reduction. This combination provides the energy efficiency and IAQ benefits of phenolic with acoustic control for the space.
How are Thermaduct System Joints sealed?
Thermaduct rectangular duct sections connect using a gasketed 4-bolt flange system. Each flange joint is lined with factory-specified EPDM or foam gasketing to create a continuous air and water seal across the entire perimeter of the connection. The flanges are mechanically fastened with bolts, ensuring a secure, uniform compression on the gasket. A weather resistant cover system is used to keep water away from the connection.
For round Thermaround systems, a sealed offset coupling with an external drawband is used. The coupling utilizes sealant and gasketing to prevent air leakage, and the drawband provides even clamping pressure around the joint.
These connection methods eliminate the need for field-applied wraps or tapes, relying instead on:
- Precision-fabricated flanges that align perfectly in the field.
- Continuous gasket compression for long-term airtightness and weather resistance.
- Protected sealing surfaces that maintain flexibility and performance through years of thermal expansion, contraction, and freeze/thaw cycles.
When installed to Thermaduct specifications, both the rectangular 4-bolt system and the round coupling system provide extremely low air leakage rates—well beyond SMACNA Class 3 performance—and maintain their integrity for the life of the system. See our online training for more information
What is the system's resistance to UV, corrosion, and chemical exposure?
UV Resistance
- Vinyl Cladding – 1000-micron, titanium-infused vinyl is UV stable and tested to resist deterioration and discoloration through extended QUV exposure testing. Available in “cool roof” color options to minimize heat gain and maintain insulation performance.
- Metal Cladding – Finished with durable coatings that resist UV degradation and maintain appearance over time, even in high-sunlight environments.
Corrosion Resistance
- Vinyl Cladding – Impervious to rust and corrosion, making it ideal for coastal, high-humidity, or industrial atmospheres.
- Metal Cladding – Multiple options to ensure compatibility with needs of the application.
Chemical Resistance
- Vinyl Cladding – Highly resistant to many environmental chemicals, acids, and alkalis, maintaining integrity in polluted or chemically exposed environments.
- Metal Cladding – Multiple options to ensure compatibility with needs of the application.
What types of cladding options does Thermaduct offer for exterior durability?
Thermaduct offers two primary cladding options for exterior durability, both factory-applied to the phenolic panel before fabrication for long-lasting performance:
UV-Stable Vinyl Cladding
- 1000-micron thick, titanium-infused vinyl for superior UV resistance.
- Highly impact resistant and up to five times thicker than many traditional duct claddings.
- Designed to for a zero perm, UV stable, appearance that maintains in extreme weather conditions.
- Offered in cool roof color options that help reduce heat buildup on the duct system.
Durable Metal Cladding
- Provides a strong, impact-resistant finish with a broader range of color options for architectural applications.
- Adds rigidity to SMACNA standards while protecting the phenolic insulation core.
- Suitable for projects where aesthetics or painting are key priorities.
Both cladding types are permanently bonded during manufacturing, eliminating the need for field-applied wraps or tapes, and protecting the system’s insulation from UV damage, moisture intrusion, and mechanical wear over time.
Can you provide data on air leakage rates under SMACNA testing?
Under SMACNA Phenolic Duct Construction Standards testing, Thermaduct’s phenolic duct systems are engineered to meet or exceed SMACNA Class 3 air leakage performance and in many cases, achieve even tighter results.
- SMACNA Class 3 requirement = Maximum leakage rate of 3% of system design airflow at 1 in. w.c. positive pressure.
- Thermaduct testing results = Systems regularly perform well above this requirement, with air leakage often approaching near-zero levels in both lab and field applications.
This performance is achieved through factory-fabricated joints, gasketed or solvent-welded seams, and full perimeter sealing using factory-specified sealants — all fabricated in accordance with SMACNA’s phenolic duct guidelines.
By delivering Class 3 or greater performance, Thermaduct reduces energy loss, protects against water intrusion, and ensures long-term system efficiency.
What is the flame spread and smoke developed index of the phenolic used in Thermaduct Products?
For Thermaduct’s phenolic-based systems, the phenolic insulation core meets the 25/50 requirement per NFPA 90A for flame spread and smoke developed index.
- Flame Spread Index: ≤ 25
- Smoke Developed Index: ≤ 50
These values indicate that the material does not support significant flame spread and produces very low levels of smoke during fire testing, which is why it is approved for use in duct applications where fire safety is critical.
This performance applies to the phenolic insulation used across Thermaduct, Thermaround, InspiralR, and Floval, whether the exterior is finished in our UV-stable vinyl cladding or our durable metal cladding.
How do Thermaduct systems perform in freeze/thaw cycles or extreme weather conditions?
Thermaduct systems are engineered for durability in harsh outdoor environments, including repeated freeze/thaw cycles, high humidity, rain, snow, hail (under golf-ball size), salt/sea spray, and wide temperature swings.
Our phenolic insulation core has greater than 90% closed-cell content, making it highly resistant to water absorption and helping preserve thermal performance over time. Whether finished with our UV-stable 1000-micron vinyl cladding or our durable metal cladding, the exterior weather barrier is factory applied, permanently bonded, and designed to withstand extreme conditions without peeling, cracking, or degrading.
These protective layers help maintain both the system’s appearance and its R-value in demanding climates, reducing the risk of moisture intrusion, freeze-related damage, or loss of efficiency.
Does Thermaduct provide layout support or assist in system sizing and routing?
Yes. Thermaduct’s engineering team can assist with system layout, sizing, and routing to ensure the duct design meets performance goals, code requirements, and installation best practices. This support includes:
- Reviewing plans for compliance with SMACNA Phenolic Duct Construction Standards and Thermaduct installation guidelines.
- Advising on duct sizing, pressure classes, and support spacing based on product capabilities.
- Recommending routing strategies to maximize efficiency, reduce air leakage, and minimize installation challenges with rectangular or round ductwork.
- Coordinating with contractors, engineers to ensure drawings translate into efficient, code-compliant installations.
While Thermaduct provides this design and layout guidance, final system design approval remains the responsibility of the project’s licensed mechanical engineer.
Can your team develop custom fittings or transitions based on our space constraints?
Yes. Each piece is precision-fabricated in our facility for long-term durability and performance expected from a Thermaduct installation. Thermaduct’s engineering and fabrication teams regularly design and manufacture custom fittings, transitions, and specialty components to address unique space limitations or architectural requirements. Common requests include offsets, tapers, non-standard terminations, and transitions to existing equipment or duct systems.
What level of design assist or design-build collaboration do you offer?
Thermaduct provides design-assist support that starts well before fabrication. Our team works with you to review drawings, determine required insulation values, and verify that the system meets your project’s temperature, pressure, and performance criteria. We confirm details such as flange types, gasket specifications, and connection methods so that every duct section is fabricated to fit precisely in the field.
In design-build settings, we can collaborate directly with your engineering and installation teams to plan routing, coordinate connection locations, and identify the best cladding option, vinyl or metal, for your environment. This early involvement helps minimize field modifications, ensures proper support spacing, and streamlines installation using our gasketed 4-bolt rectangular connections or sealed drawband round connections.
By aligning fabrication details with project requirements from the outset, we help you achieve a high-performance, low-leakage outdoor duct system that installs quickly and maintains its efficiency for years to come.
Are your products SMACNA Compliant?
Thermaduct rectangular products are engineered to meet or exceed the SMACNA Duct Construction & Phenolic Duct Construction Standards, recognized worldwide as the benchmark for HVAC duct construction. Although these standards do not yet apply to round or flat oval configurations, all Thermaduct systems are manufactured with the same rigorous focus on safety, durability, and long-term performance.
How do you comply with UL 181, NFPA 90A or ASTM E84 testing requirements?
Thermaduct products use a phenolic insulation core that meets the requirements of UL 181, NFPA 90A, and ASTM E84 testing. InspiralR and Floval indoor systems are UL 181 Listed, and all Thermaduct products meet NFPA 90A’s 25/50 requirement for flame spread and smoke developed index. The phenolic core has also been tested to ASTM E84 and meets the same 25/50 classification.
Are your systems able to be used in high-humidity, coastal or seismic zones?
Yes. Thermaduct systems are engineered for durability in demanding environments, including high-humidity regions, coastal areas with salt/sea spray, and locations subject to seismic activity. The phenolic insulation core has greater than 90% closed-cell content, making it highly resistant to water absorption, and is protected by either our UV-stable 1000-micron vinyl cladding or our durable metal cladding for long-term corrosion resistance.
In coastal and high-humidity conditions, this combination prevents moisture intrusion and protects R-values over time. For seismic zones, Thermaduct follows SMACNA Phenolic Duct Construction Standards and can be supported with engineered hanger and bracing designs to meet local seismic code requirements. Final seismic restraint design should be reviewed and approved by the project’s licensed engineer.
Do your systems meet state or federal energy codes?
Yes. Thermaduct systems are designed to meet or exceed the insulation and air leakage requirements outlined in ASHRAE 90.1, the International Energy Conservation Code (IECC), and most state or federal energy codes. With available insulation values ranging between R-8 to R-24 for outdoor and R-6 for our indoor round systems, our products can be specified to match or surpass the minimum duct insulation levels required in your jurisdiction.
Are LEED credits available based on your product's attributes?
Yes. Thermaduct products can contribute toward LEED credits in several categories, depending on your project’s certification goals. While LEED credits are awarded to the project—not to individual products—our systems support credit achievement through attributes such as high thermal performance, low air leakage, and improved indoor air quality.
Can your facility scale to accommodate a project of this size?
Yes. In addition to our own production capabilities, Thermaduct works with a network of licensed fabricators across the country, allowing us to scale quickly to meet the demands of large or fast-track projects. For example, on data center projects with aggressive startup timelines, we’ve coordinated production through three separate licensed fabricators simultaneously to ensure all duct sections were delivered on schedule. This flexibility allows us to maintain product quality while meeting even the most challenging project timelines.
Do you use automated or manual fabrication processes?
Our fabrication process is primarily manual, which allows for the precision and quality control required for each custom project. However, we continually evaluate and incorporate automation where it can improve efficiency, consistency, or turnaround times. This balance ensures that every Thermaduct product meets our performance standards while allowing us to streamline production as new technologies and processes become available.
What quality control measures are in place during manufacturing?
Thermaduct follows detailed fabrication guidelines that go beyond the requirements of the SMACNA Phenolic Duct Construction Standards. Every product manufactured, whether in our headquarter facility or by a licensed fabricator, adheres to these guidelines to ensure consistent fabrication practices, precise assembly, and long-term performance. By exceeding industry standards and enforcing uniform procedures across our network, we ensure each duct section meets the same high level of quality before it leaves the shop.
Are your components manufactured in the U.S., or are any parts imported?
Thermaduct sources its phenolic panels and certain limited components from trusted international manufacturers. However, the majority of our manufacturing materials—and all fabrication labor—are U.S.-based. Our processes comply with the Build America, Buy American Act requirements, ensuring that our products meet federal procurement standards while delivering the performance and quality expected from Thermaduct systems.
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