Related Resources: heat transfer

Minimum Duct Insulation R-Value

Heat Transfer Knowledge and Engineering
HVAC Engineering

Minimum Duct Insulation R-Value,^a Cooling and Heating-Only Supply Ducts and Return Ducts

Thermal insulation is commonly used to reduce energy consumption of HVAC systems and equipment. Minimum insulation levels for ductwork and piping are often dictated by energy codes, many of which are based on ASHRAE Standards 90.1 and 90.2. In many cases, it may be cost-effective to go beyond the minimum levels dictated by energy codes. Thicknesses greater than the optimum economic thickness may be required for other technical reasons such as condensation control, personnel protection, or noise control.

Duct Location
Climate Zoned	Exterior	Ventilated Attic	Unvented Attic Above Insulated Ceiling	Unvented Attic with Roof Insulationa	Unconditioned Spaceb	Indirectly Conditioned Spacec	Buried
1, 2	none	none	none	none	none	none	none
3	R-3.5	none	none	none	none	none	none
4	R-3.5	none	none	none	none	none	none
5	R-6	R-3.5	none	none	none	none	R-3.5
6	R-6	R-6	R-3.5	none	none	none	R-3.5
7	R-8	R-6	R-6	none	R-3.5	none	R-3.5
8	R-8	R-8	R-6	none	R-6	none	R-6
Cooling-Only Ducts
1	R-6	R-6	R-8	R-3.5	R-3.5	none	R-3.5
2	R-6	R-6	R-6	R-3.5	R-3.5	none	R-3.5
3	R-6	R-6	R-6	R-3.5	R-1.9	none	none
4	R-3.5	R-3.5	R-6	R-1.9	R-1.9	none	none
5, 6	R-3.5	R-1.9	R-3.5	R-1.9	R-1.9	none	none
7, 8	R-1.9	R-1.9	R-1.9	R-1.9	R-1.9	none	none
Return Ducts
1 to 8	R-3.5	R-3.5	R-3.5 n	one	none	none	none

^a Insulation R-values, measured in h·ft²·°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. 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 crawlspaces, both ventilated and nonventilated.
^c Includes return air plenums with or without exposed roofs above.
^d Climate zones for the continental United States defined in ASHRAE Standard 90.1-2010.

Climate Zones Map
(Click on image to enlarge)

Related:

• Insulation Material Thermal Conductivity Chart
• Insulation Blanket Applications and Capabilities Overview
• Time to Freeze Piping Formulas and Calculator
• Insulating Materials Thermal Properties
• Heat Loss Insulated Pipe Equation and Calculator
• Heat Loss Insulated Electric Wire Equations and Calculator
• Insulation Resistance for Electrical Equipment Calculator Spreadsheet

Reference:

• ASME Code for Pressure Piping, B31.5, Refrigeration Piping and Heat Transfer Components