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2. Duct (flow) - Wikipedia

   en.wikipedia.org/wiki/Duct_(flow)

   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 get the full internal diameter.

3. Building insulation material - Wikipedia

   en.wikipedia.org/wiki/Building_insulation_material

   Closed-cell foams are superior insulators. While open-cell foams typically have R-values of 3 to 4 per inch (RSI-0.53 to RSI-0.70 per inch), closed-cell foams can attain R-values of 5 to 8 per inch (RSI-0.88 to RSI-1.41 per inch). This is important if space is limited, because it allows a thinner layer of insulation to be used.

4. Pipe insulation - Wikipedia

   en.wikipedia.org/wiki/Pipe_insulation

   Insulated hot water supply and return hydronic piping on a gas-fired boiler. Since pipework can operate at temperatures far removed from the ambient temperature, and the rate of heat flow from a pipe is related to the temperature differential between the pipe and the surrounding ambient air, heat flow from pipework can be considerable.

5. Cross-linked polyethylene - Wikipedia

   en.wikipedia.org/wiki/Cross-linked_polyethylene

   A cross-linked polyethylene (PEX) pipe. Cross-linked polyethylene, commonly abbreviated PEX, XPE or XLPE, is a form of polyethylene with cross-links.It is used predominantly in building services pipework systems, hydronic radiant heating and cooling systems, domestic water piping, insulation for high tension (high voltage) electrical cables, and baby play mats.

6. Process duct work - Wikipedia

   en.wikipedia.org/wiki/Process_Duct_Work

   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.

7. Electrical conduit - Wikipedia

   en.wikipedia.org/wiki/Electrical_conduit

   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.