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Our September email addresses two common project requirements that are often difficult to specify so that they meet system life expectancy with minimal, if any, maintenance and still be cost competitive. Ductwork located outdoors is found on many projects yet its construction, insulation, weatherproofing, and maintenance are often major concerns. Field insulated and weatherproofed outdoor ductwork requires skill to construct and care to maintain the required insulating value and to prevent water intrusion into the ductwork and structure. The multi-step construction process usually requires weather dependent coordination between two trades that can result in construction delays. Shortly after installation it is very common for outdoor duct insulation to experience moisture penetration that renders the insulation nearly valueless and, unless a water leak is apparent in the building, can exist until the system is renovated. Wet insulation increases operating costs and the potential for mold/indoor air quality issues. Fortunately there is a solution that eliminates all of these problems at an affordable price-Thermaduct.
Thermaduct, a pre-insulated, pre-engineered phenolic duct system available in rectangular or round, consists of closed cell rigid insulation bonded on both sides to factory applied 25 micron aluminum foil facing. The exterior cladding is UV stable, IR reflective 1000-micron high impact resistant titanium infused vinyl that is factory bonded using a full lamination process. The lamination process permanently bonds the vinyl cladding to the outer surfaces of the phenolic foam panel to provide a zero-permeability water tight barrier and forms a structurally insulated panel. The New Jersey and New York 2015 Mechanical Codes, the 2014 New York City Mechanical Code and the 2018 Uniform Mechanical Code address non-metallic duct construction applications. All Thermaduct products conform to these codes and the SMACNA phenolic duct construction standard.
Transverse connections are made with 4-bolt flanges, covered with foam insulation tape and a vinyl weather cover. Contrary to other manufacturer’s designs, no exposed fasteners are used so that no water penetration is possible. An internal framing system that exceeds SMACNA standards is installed at the factory to handle internal and external static loads and dynamic loads such as wind, snow and rain.
Thermaduct provides solutions for equipment connections, curbs, wall penetrations, access doors, field installed modifications and branch connections:
Thermaduct benefits include:
  • Thermaduct 10 year limited warranty
  • Long term weather resistance (including ≈1” hail) and salt/sea spray
  • Completely factory assembled and sealed duct sections
  • Specifiable insulation values from R8.1 through R24 for rectangular, R12 minimum for round
  • Long term duct insulating value retention
  • Construction to ±10” static pressure
  • Duct air leakage rate complying with the SMACNA HVAC Duct Construction Standards per the applicable leakage class
  • Reduced energy consumption and operating costs for the life of the installation
  • Thermaduct provided drawings for approval that include recommended support locations
  • Prevention of mold growth and indoor air quality issues
  • 35-40% lower weight than field insulated and weatherproofed sheet metal ductwork
  • Suitable for clean air applications between -15⁰F and +185⁰F
  • Air friction equivalent to galvanized sheet metal friction
  • Fiber free air stream - perfect for many hospital type applications
  • Up to 4 LEED point eligible-Material and Ingredients, Sourcing of Raw Materials
  • UL-181 mold growth test compliance
  • UL-94 flammability V-0
  • Rapid field erection, e.g., approximately 10 minutes for a man to join and seal two 30” x 30” duct sections
  • No exposed screws or fasteners
  • Tear and puncture resistant vinyl cladding
  • Available in white, tan or gray exterior
Indoor applications use Thermaduct’s ultra-low leakage round and flat oval, R-6 insulated phenolic duct systems. These factory assembled and insulated systems save significant construction time with weight savings up to 75% compared to insulated sheet metal.
RTS-Rooftop Support Systems, also represented by Samuel Tepp Associates, provides cost effective, rapidly specified and constructed supports perfect for Thermaduct and any other roof support applications. RTS provides solutions that require only bolting fittings and strut together for both non-penetrating or direct mount applications. RTS solutions are factory fabricated meet to any project’s dimensions, offer rapid installation, and easily accommodate field modifications.  In addition to duct supports, RTS provides pipe and equipment supports, cross over ramps, stairways and equipment access platforms. RTS has developed many standard designs to simplify assembly, minimize cost and their in-house design engineers quickly provide economical custom designs. PE stamped structural calculations are available to address wind, seismic and snow loads. RTS’ supports are factory fabricated with either pre-galvanized steel or stainless steel materials with optional finishes including hot dipped galvanizing, powder coating, and plating.
More information on Thermaduct and RTS products are on line at and as well as by contacting me. Please give me a call to discuss your projects and to schedule our lunch/learn on Thermaduct and RTS applications that is approved for one PDH for New Jersey, New York, and Pennsylvania PE’s. A summary of all of our engineering topics, all approved by New Jersey, New York and Pennsylvania for PE continuing education credits, is on our website

Engineering Tidbit-Variable Frequency Drives
Variable frequency drives can provide major energy savings and expand design options and Samuel Tepp’s long representation of Eaton VFD’s includes in-depth application support as well as VFD programming and commissioning. While VFD’s have been commonly applied for over twenty years there are a few application issues to be considered:
  1. VFD’s are shipped from manufacturers with limited pre-programmed operating sequences and frequently require field programming.
  2. VFD specifications should specify if they are to be provided with bypasses. Bypasses, which enable the motor to run at full speed if the drive fails, were viewed as essential when VFD’s were first introduced. VFD reliability has improved dramatically since that time and their need should be carefully considered. Bypass operation, if not carefully evaluated, can result in high system pressure and damage.
  3. Motor cable lengths must comply with motor manufacturer recommendations.
  4. VFD’s can induce current flow through the motor shaft and bearings. Facilities with many large motors should consider the use of grounding methods to dissipate the shaft current and prevent rapid bearing/motor failure.
Samuel Tepp Associates strives to provide the best technical support in the industry. As part of this support, our monthly emails and our engineering seminars are designed to provide information and to open dialogs on engineering topics relevant to consulting engineers. I hope you found this email informative and look forward to receiving your comments. If there are topics you would like covered or have any questions, please give me a call.
Keith Miller
Samuel Tepp Associates
Cell: 201-638-6591

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