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Thermaflex® 8" R-KD R4.2 Flex-Vent Insulated Flexible Air Duct (Box)

Item: FD-8X25-R42MH
MFR: 056508000001

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About This Product

Product Info


Thermaflex® R-KD duct is a thermally insulated, fully lined, UL 181 Class I flexible air duct designed for efficient installation and operation in outdoor cooling and heating systems of low and medium pressure. It is available in standard 25-foot lengths. Because of its extreme flexibility and good weathering characteristics, Thermaflex® R-KD is particularly suitable for add-on mobile home remote air conditioning, for connecting double wide units as crossover duct, and for use in modular building systems. Thermaflex RK-D complies with HUD Mobile Home Construction and Safety Code Part 3280.715, Chapter II of 24 CFR. It provides an economical means for handling misalignment between system components and ducting around obstacles where fabricated and fitted ducts are difficult and costly to install.

  • Reduced total installed cost fast, economical installation
  • Underwriters Laboratories listed UL 181 Class I Air Duct. Also complies with HUD Mobile Home Construction and Safety Code Part 3280.715, Chapter II of 24 CFR; NFPA Standards 90A and 90B, and most local, state and federal standards or codes
  • Factory applied extra thick thermal insulation blanket complies with HUD/FHA minimum property standard; also HUD Mobile Home Construction and Safety Code
  • Large diameter, heavy, spring steel wire helix assures dimensional stability, resists mechanical abuse and provides more efficient air delivery
  • Core constructed of multiple layers of strong polyester film encapsulating a heavy corrosion-resistant spring steel helix
  • Inner core oversized for quick instillation
  • Outward cast of heavy steel spring steel helix keeps duct core from shrinking up inside insulation and jacket resulting in less waste
  • Labor savings and reduced waste result in lower installed costs
  • Quality R-KD installations produce referrals that increase volume and profits
  • Available in certified R-4.2 thermal values
Warning: this product contains a chemical known to the State of California to cause cancer.


Weight10.4 Pounds (lbs)
Width8 Inches (In)
Height11.375 Inches (In)
Country of OriginUSA
Length11.375 Inches (In)
ApplicationAir Distribution
ColorBlack, Pink
Comments/NotesUL Listed - USA & CAN
ComplianceNFPA 90 A and 90 B
CompositionLaminated Polyester duct liner is permanently bonded to a corrosion-resistan spring steel wire helix. Also supporting a thick blanket of fiberglass insulation and fiberglass scrim vapor barrier is an outer jacket of heavy Black polyethylene.
Core MaterialPolyester Film
Fire RatingMeets UL 181 & NFPA 90A-90B Fire Codes
Inside Diameter8"
Jacket MaterialVapor Barrior
Maximum Air Flow5000 FPM
Maximum PressurePositive = 6" (6-14" ID) Negative = 1" (6-12" ID) 1/2" (14" ID)
Maximum Temperature250°F (121.1°C)
Operating Temperature-20°F to 250°F (-28.8°C to 121.1°C)
Pressure RatingWG - Positive 6 inches (18"-20" ID) - Negative 1/2 inch (6"-12" ID)
Prop 65Yes
Size8" x 25'
Vapor Transmission0.1
Warranty OfferedYes


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