ASHRAE-90.1-2022- - Page 138
Extracted Content
Table 6.8.2 Minimum Duct Insulation R-Value [a]
Climate Zone
Duct Location
Exterior [ b] Unconditioned Space and Buried Ducts Indirectly Conditioned Space [ c,d]
Supply and Return Ducts for Heating and Cooling
0 to 4 R-8 R-6 R-1.9
5 to 8 R-12 R-6 R-1.9
Supply and Return Ducts for Heating Only
0 to 1 None None None
2 to 4 R-6 R-6 R-1.9
5 to 8 R-12 R-6 R-1.9
Supply and Return Ducts for Cooling Only
0 to 6 R-8 R-6 R-1.9
7 to 8 R-1.9 R-1.9 R-1.9
a. Insulation R-values, measured in h·ft [2] ·°F/Btu, are for the insulation as installed and do not include film resistance. The required minimum thicknesses
do not consider water vapor transmission and possible surface condensation. Where portions of the building envelope are used as a plenum enclosure, building envelope insulation shall be as required by the most restrictive condition of Section 6.4.4.1 or Section 5, depending on whether the plenum is located in the roof, wall, or floor . Insulation resistance measured on a horizontal plane in accordance with ASTM C518 at a mean temperature of 75°F at the installed thickness. b. Includes attics above insulated ceilings, parking garages and crawl spaces . c. Includes return air plenums with or without exposed roofs above. d. Return ducts in this duct location do not require insulation.
Table 6.8.3-1 Minimum Piping Insulation Thickness Heating and Hot-Water Systems [a,b,c,d] []
(Steam, Steam Condensate, Hot-Water Heating and Domestic Water Systems)
Insulation Thermal Conductivity Nominal Pipe or Tube Size, in.
Fluid Operating Temperature Range ( F)
and Usage
Conductivity, Btu·in/h·ft [2] · F
Mean Rating Temperature, F
<1 1 to <1-1/2 1-1/2 to <4 4 to <8 8
Insulation Thickness, in.
350 0.32 to 0.34 250 4.5 5.0 5.0 5.0 5.0
251 to 350 0.29 to 0.32 200 3.0 4.0 4.5 4.5 4.5
201 to 250 0.27 to 0.30 150 2.5 2.5 2.5 3.0 3.0
141 to 200 0.25 to 0.29 125 1.5 1.5 2.0 2.0 2.0
105 to 140 0.22 to 0.28 100 1.0 1.0 1.5 1.5 1.5
For service water heating systems, see Table 7.4-2.
a. These thicknesses are based on energy efficiency considerations only. Additional insulation is sometimes required relative to safety issues/surface temperature. b. For piping smaller than 1.5 in. and located in partitions within conditioned spaces, reduction of these thicknesses by 1 in. shall be permitted (before thickness adjustment required
in footnote [a]) but not to thicknesses below 1 in. c. For direct-buried heating and hot-water system piping, reduction of these thicknesses by 1.5 in. shall be permitted (before thickness adjustment required in footnote [a]) but not
to thicknesses below 1 in. d. Piping that also serves service water heating systems shall comply with Section 7.4.
Table 6.8.3-2 Minimum Piping Insulation Thickness Cooling Systems (Chilled Water, Brine, and Refrigerant) [a,b]
Insulation Thermal Conductivity Nominal Pipe or Tube Size, in.
Fluid Operating
Temperature Range ( F) and Usage
<1 1 to <1-1/2 1-1/2 to <4 4 to <8 8
Insulation Thickness, in.
Conductivity, Btu·in/h·ft [2] · F
Mean Rating Temperature, F
40 to 60 0.21 to 0.27 75 0.5 0.5 1.0 1.0 1.0
<40 0.20 to 0.26 50 0.5 1.0 1.0 1.0 1.5
a. These thicknesses are based on energy efficiency considerations only. Issues such as water vapor permeability or surface condensation sometimes require vapor retarders or addi tional insulation. b. For direct-buried cooling system piping, insulation is not required.
136 ANSI/ASHRAE/IES Standard 90.1-2022 (I-P)