Ductwork
Ducts are used either for warm air heating or air conditioning. Warm Air Insulate for energy conservation in accordance with the Building Regulations, Approved Document L1. 1.39 Unless the heat loss from a pipe or duct contributes to the useful heat requirement of a room or space the pipe or duct shall be insulated. The requirement would be satisfied for warm air ducts and in the case of pipes if insulation is provided in accordance with the recommendations of BS 5422:1990 table 16 Temperature difference between ambient and air inside duct 10 K 25 K 50 K Class O Armaflex 32 38 50 NH/Armaflex 38 44 63 HT/Armaflex 38 44 63 These Armaflex thickness recommendations are in broad agreement with the insulated heat loss values quoted in BS 5422:1990 Table 16 “Economic thickness of insulation on ductwork carrying warm air”. Air Conditioning Insulate for condensation control, as a minimum requirement. Additional insulation thickness may be desirable to reduce heat gain. Chilled Air in Warm Space Minimum commercially available thicknesses of Class O Armaflex and NH/Armaflex insulation for condensation control on ductwork carrying chilled air. Ambient conditions Insulation Air temperature inside duct Temp. Rel. humidity 15 °C 10 °C 5 °C 0 °C 25 °C 80% Class O Armaflex 6 mm 13 mm 19 mm 25 mm NH/Armaflex 9 mm 19 mm 25 mm 25 mm HT/Armaflex 9 mm 19 mm 25 mm 25 mm 20 °C 70% Class O Armaflex 6 mm 6 mm 6 mm 13 mm NH/Armaflex 6 mm 6 mm 9 mm 13 mm HT/Armaflex 6 mm 6 mm 9 mm 13 mm Air temperature 25 ºC and relative humidity 80% are the ambient conditions used in the calculation of Table 16 in BS 5422 : 1990 for a material with high emissivity. Vapour barrier For chilled air ductwork it is a technical requirement that a vapour barrier shall be applied on the exposed face. The permeance shall not exceed 0.05 g/(s.MN). All Armaflex thermal insulation materials exceed this requirement at the thickness shown above.
Related information: Specification Form - Ductwork

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