Thermaduct LLC v. Albers Sheetmetal Ventilating Inc

I. Executive Summary and Procedural Information

• Parties & Counsel:
  • Plaintiff: Thermaduct, LLC (Ohio)
  • Defendant: Albers Sheetmetal and Ventilating, Inc. d/b/a Ducts and Cleats (Minnesota)
  • Plaintiff’s Counsel: Carlson, Caspers, Vandenburgh & Lindquist, P.A.; Harness, Dickey & Pierce, P.L.C.
• Case Identification: 0:26-cv-00963, D. Minn., 02/02/2026
• Venue Allegations: Venue is asserted based on the Defendant residing in the District of Minnesota, maintaining a regular and established place of business in the district, and committing the alleged acts of infringement within the district.
• Core Dispute: Plaintiff alleges that Defendant’s Pro-R Duct product line infringes a patent related to structurally reinforced, pre-insulated HVAC ducts.
• Technical Context: The technology involves methods for reinforcing lightweight, foam-based HVAC ductwork to withstand significant internal pressure and external loads, making it suitable for demanding outdoor applications.
• Key Procedural History: The complaint alleges a significant prior business relationship, stating that from 2013 to 2019, Defendant was an authorized fabricator of Plaintiff's patented duct system. The complaint further alleges that Defendant was made aware of the patent-pending technology during this relationship, cited Plaintiff's patent publication in its own patent filings, and launched the accused competing product after Plaintiff terminated the fabrication agreement in 2019.

Case Timeline

II. Technology and Patent(s)-in-Suit Analysis

U.S. Patent No. 9,995,503 - "Structurally Reinforced Duct"

• Patent Identification: U.S. Patent No. 9,995,503, "Structurally Reinforced Duct", issued June 12, 2018.

The Invention Explained

• Problem Addressed: The patent addresses the structural limitations of conventional insulated foam panel ducts, which may lack the strength and rigidity to withstand "extreme external loading" (such as snow) and "extreme internal pressure loading" without failing or deforming (Compl. ¶13; '503 Patent, col. 1:1-6).
• The Patented Solution: The invention describes a reinforcement system for foam panel ducts that uses both internal and external components to counteract forces. The system comprises internal ribs on opposing duct walls connected by a "compression member" (e.g., a strut) to prevent the walls from bowing inward ('503 Patent, abstract; '503 Patent, col. 2:64-3:2). Simultaneously, an external "tension member" (e.g., a threaded rod) connects "force distribution members" (e.g., plates) on the outside of the same walls to prevent them from bowing outward under internal pressure ('503 Patent, abstract; '503 Patent, col. 3:56-62).
• Technical Importance: This dual internal/external reinforcement system allows lightweight, high-insulation foam ducts to be used in demanding structural applications, such as on rooftops, that were traditionally reserved for heavier sheet metal ductwork (Compl. ¶¶13, 22).

Key Claims at a Glance

• The complaint asserts independent claim 1 Compl. ¶66
• The essential elements of independent claim 1 include:
  • A duct section made of foam panel side walls.
  • A first and second longitudinal "rib" on the inside surfaces of two opposed, parallel side walls.
  • A "compression member" secured between the ribs to prevent the walls from moving towards each other.
  • First and second "force distribution members" on the outside surfaces of the same side walls.
  • A "tension member" connecting the force distribution members to prevent the walls from moving away from each other.
  • A first and second "flange" secured to the ends of the side walls.
  • "Fasteners" connecting the ends of the ribs to portions of the flanges.
• The complaint reserves the right to assert additional claims of the ’503 Patent Compl. ¶66

III. The Accused Instrumentality

Product Identification

• The accused product is Defendant's "Pro-R Duct," specifically versions that include the "ProTruss" reinforcement system Compl. ¶44 Compl. ¶58

Functionality and Market Context

• The Pro-R Duct is advertised as a pre-assembled, pre-insulated, and efficient ductwork solution Compl. ¶46 Marketing materials submitted with the complaint describe the "ProTruss" system as a method for reinforcing the duct for "higher static pressure needs," which "integrates with tie rod supports and connects from flange to flange" Compl., Ex. 14, p. 23
• A diagram from Defendant's brochure shows the "ProTruss Reinforcement Method Detail," which includes an "Interior ProTruss Plate with Two Standing Seams," "Tie Rods," and external reinforcement plates Compl., Ex. 13, p. 23
• The complaint alleges that the Pro-R Duct with the ProTruss system is a "knockoff" or "copycat" of Plaintiff's patented "Thermaduct System with Airtruss reinforcement," which Defendant began selling after Plaintiff terminated a multi-year agreement under which Defendant had been a fabricator of Plaintiff's system (Compl. ¶¶44, 55).

IV. Analysis of Infringement Allegations

'503 Patent Infringement Allegations

• Identified Points of Contention:
  • Structural Questions: A potential dispute may arise over whether the accused "Interior ProTruss Plate with Two Standing Seams" Compl., Ex. 13, p. 23 constitutes the "first rib" and "second rib" as two distinct elements required by the claim, or if it is a single, structurally different component.
  • Functional Questions: The patent describes a "compression member" and a "tension member" that perform opposing functions. The accused product's marketing clearly identifies "Tie Rods" Compl., Ex. 13, p. 23 that appear to function as tension members. A key question will be what evidence the complaint provides that the accused product also contains a distinct "compression member" operable to prevent the walls from moving towards each other, as required by the claim.

V. Key Claim Terms for Construction

• The Term: "compression member"
• Context and Importance: The identification of a "compression member" in the accused product is central to the infringement allegation. Defendant may argue that its "ProTruss" system, which uses "tie rods," is a tension-only system and lacks the claimed compressive element. Practitioners may focus on this term because the patent's drawings depict the compression member and tension member as separate components, raising the question of whether a single structure can satisfy both limitations or if the accused product has a compressive element at all.
• Intrinsic Evidence for Interpretation:
  • Evidence for a Broader Interpretation: The specification states the component "may have any configuration that achieves the function of the compression member, namely, to resist movement of the ribs 28 and 30 towards each other" ('503 Patent, col. 3:4-8). This language may support a functional interpretation that is not limited to a specific structure.
  • Evidence for a Narrower Interpretation: The patent's abstract and detailed description consistently describe the "compression member" and "tension member" as separate elements that counteract opposing forces ('503 Patent, abstract). The embodiments shown in Figures 1-5 depict the compression member (38) as a distinct physical strut separate from the tension member (46), which may support an interpretation requiring separate structures.

VI. Other Allegations

• Indirect Infringement: The complaint alleges inducement by citing Defendant's marketing materials, brochures, and sales presentations Compl., Exs. 8, 13, 14, which allegedly instruct and encourage customers and installers to use the Pro-R Duct in an infringing manner (Compl. ¶¶68, 70-73). The complaint also alleges contributory infringement, stating the Pro-R Duct is a material component of the invention and is not a staple article of commerce with substantial non-infringing uses Compl. ¶¶74-75
• Willful Infringement: The complaint makes extensive allegations to support willfulness. It claims Defendant had pre-suit knowledge of the '503 patent and its technology based on: (1) a prior business relationship (2015-2019) as a fabricator of Plaintiff's patented system Compl. ¶39; (2) alleged direct notice from the inventor in 2015 that the technology was patent-pending Compl. ¶49; (3) Defendant's own 2017 provisional patent application that cited Plaintiff's published application Compl. ¶¶50-51; and (4) an Information Disclosure Statement filed in 2022 during prosecution of Defendant's own patent, which cited the issued '503 patent Compl. ¶52 Compl. ¶79

VII. Analyst’s Conclusion: Key Questions for the Case

• A core issue will be one of structural identity: can the Defendant's "ProTruss" system, described as an "Interior ProTruss Plate with Two Standing Seams," be proven to meet the claim limitations of a "first rib," a "second rib," and a "compression member," or does it represent a materially different, non-infringing design?
• A second central question will concern willfulness and damages, hinging on the extensive factual allegations of the parties' prior business relationship. The court's determination will likely depend on evidence of Defendant's pre-suit knowledge of the patent and the timing and nature of its development of the accused Pro-R Duct after the termination of its role as Plaintiff's fabricator.