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Kinks in flexible ducting must be avoided. Some flexible duct markets prefer to avoid using flexible duct on the return air portions of HVAC systems, however flexible duct can tolerate moderate negative pressures. The UL181 test requires a negative pressure of 200 Pa. To use flexible ducting in a system, make sure to pull the duct tight so you ...
Flexible metallic tubing (FMT; North America) is not the same as flexible metallic conduit (FMC) which is described in US National Electrical Code (NEC) Article 348. FMT is a raceway, but not a conduit and is described in a separate NEC Article 360. It only comes in 1/2" & 3/4" trade sizes, whereas FMC is sized 1/2" ~ 4" trade sizes.
Pipe insulation made from rigid Phenolic, PIR, or PUR foam insulation is common in some countries. Rigid-foam insulation has minimal acoustic performance but can exhibit low thermal-conductivity values of 0.021 W/(m·K) or lower, allowing energy-saving legislation to be met whilst using reduced insulation thicknesses. [8]
Polyurethane is a closed-cell foam insulation material that initially contains a low-conductivity gas in its cells. [6] As a result of the high thermal resistance of the gas, spray polyurethane insulation typically has an initial R-value around R-3.4 to R-6.7 per inch. [6] In comparison, glass wool typically has an R-Value of only R-3 to R-4 ...
While pipe sizes in Australia are inch-based, they are classified by outside rather than inside diameter (e.g., a nominal 3 ⁄ 4 inch copper pipe in Australia has measured diameters of 0.750 inches outside and 0.638 inches inside, whereas a nominal 3 ⁄ 4 inch copper pipe in the U.S. and Canada has measured diameters of 0.875 inch outside and ...
In the background of this photo is a duct flange. The duct flange normally has 3/4" bolts at 6" nominal; spacing. Duct flange angle thickness needs to be designed for duct plate tensile stresses, as flanges will bend. 5/16" or 3/8" angle thicknesses are common. See above photo of round duct elbows, transitions, and stiffeners.
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