Wash. Admin. Code § 51-11C-40391
Ducts conveying outdoor air shall be insulated continuously from the building exterior to an automatic shutoff damper or heating or cooling equipment. Duct surfaces shall be insulated with the minimum insulation values in Table C403.10.1.1. Duct surfaces included as part of the building envelope shall not be used in the calculation of maximum glazing area as described in Section C402.4.1.
EXCEPTION: | Outdoor air ducts serving individual supply air units with less than 2,800 cfm of total supply air capacity, provided these are insulated to the minimum insulation values in Table C403.10.1.1. |
Table C403.10.1.1 Outdoor Air Ductwork Insulation
Duct system | Duct Location and Use | Climate Zone | Airflow | Minimum Installed Duct Insulation R-valuea,b | Notes |
Outdoor Air | Inside conditioned space and upstream of automatic shutoff damper | 4C and 5B | [GREATER THAN EQUAL TO] 2800 CFM | R-16 | See Section C403.10.1.1 for additional requirements |
Outdoor Air | Inside conditioned space and downstream of automatic shutoff damper to HVAC unit or room | 4C | [GREATER THAN EQUAL TO] 2800 CFM | R-8 | |
Outdoor Air | Inside conditioned space and downstream of automatic shutoff damper to HVAC unit or room | 5B | [GREATER THAN EQUAL TO] 2800 CFM | R-12 | |
Outdoor Air | Inside conditioned space | 4C and 5B | [LESS THAN EQUAL TO] 2800 CFM | R-7 | See Exception 1 to Section C403.10.1.1 for additional details |
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 See International Mechanical Code Sections 603.12 and 604 for further details on duct insulation requirements.
EXCEPTIONS: | 1.Where located within equipment. 2.Supply and return ductwork located in unconditioned spaces where the design temperature difference between the interior and exterior of the duct or plenum does not exceed 15°F (8°C) and are insulated in accordance with Table C403.10.1.2. |
Where located within conditioned space, supply ducts which convey supply air at temperatures less than 55°F or greater than 105°F shall be insulated with a minimum insulation R-value in accordance with Table C403.10.1.2.
EXCEPTION: | Ductwork exposed to view within a zone that serves that zone is not required to be insulated. |
Where located within conditioned space, return or exhaust air ducts that convey return or exhaust air downstream of an energy recovery media shall be insulated with a minimum insulation R-value in accordance with Table C403.10.1.2.
All ducts, air handlers, and filter boxes shall be sealed. Joints and seams shall comply with Section 603.9 of the International Mechanical Code.
Table C403.10.1.2 Supply, Return, Exhaust and Relief Air Ductwork Insulation
Duct system | Duct Location and Use | Climate Zone | Minimum Installed Duct Insulation R-valuea,b | Notes |
Supply air or return air | Outside the building (outdoors and exposed to weather)c | 4C | R-8 | See Section C403.10.1.2 for details |
Supply air or return air | Outside the building (outdoors and exposed to weather)c | 5B | R-12 | See Section C403.10.1.2 for details |
Supply air or return air | Unconditioned space (enclosed but not in the building conditioned envelope) | 4C and 5B | R-6 | See Section C403.10.1.2 for details |
Supply air or return air | Unconditioned space where the duct conveys air that is within 15°F of the air temperature of the surrounding unconditioned space | 4C and 5B | R-3.3 | See IMC Section 603.12 for additional requirements for condensation control at ductwork |
Supply air or return air | Where located in a building envelope assembly | 4C and 5B | R-16 | Duct or plenum is separated from building envelope assembly with the minimum insulation value |
Supply air | Within conditioned space where the supply duct conveys air that is less than 55°F or greater than 105°F | 4C and 5B | R-3.3 | See Section C403.10.1.2 for details |
Supply air | Within conditioned space that the duct directly serves where the supply duct conveys air that is less than 55°F or greater than 105°F | 4C and 5B | None | See Section C403.10.1.2 for details |
Supply air | Within conditioned space where the supply duct conveys air that is 55°F or greater and 105°F or less | 4C and 5B | None | |
Return or exhaust air | Within conditioned space, downstream of an energy recovery media, upstream of an automatic shutoff damper | 4C | R-8 | |
Return or exhaust air | Within conditioned space, downstream of an energy recovery media, upstream of an automatic shutoff damper | 5B | R-12 | |
Relief or exhaust air | Conditioned space and downstream of an automatic shutoff damper | 4C and 5B | R-16 |
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 See International Mechanical Code Sections 603.12 and 604 for further details on duct insulation requirements.
c Includes attics above insulated ceilings, parking garages and crawl spaces.
EXCEPTION: | Continuously welded and locking-type longitudinal joints and seams on ducts operating at static pressures less than 2 inches water gauge (w.g.) (500 Pa) pressure classification. |
Documentation shall be furnished demonstrating that representative sections totaling at least 25 percent of the duct area have been tested and that all tested sections meet the requirements of this section.
EXCEPTIONS: | 1. Factory-installed piping within HVAC equipment tested and rated in accordance with a test procedure referenced by this code. 2. Factory-installed piping within room fan-coils and unit ventilators tested and rated according to AHRI 440 (except that the sampling and variation provisions of Section 6.5 shall not apply) and 840, respectively. 3. Piping that conveys fluids that have a design operating temperature range between 60°F (15°C) and 105°F (41°C). 4. Piping that conveys fluids that have not been heated or cooled through the use of fossil fuels or electric power. 5. Strainers, control valves, and balancing valves associated with piping 1 inch (25 mm) or less in diameter. 6. Direct buried piping that conveys fluids at or below 60°F (15°C). 7. In radiant heating systems, sections of piping intended by design to radiate heat. |
Table C403.10.3 Minimum Pipe Insulation Thickness (thickness in inches)a
Fluid Operating Temperature Range and Usage (°F) | Insulation Conductivity | Nominal Pipe or Tube Size (Inches) | |||||
Conductivity Btu *In. /(h * ft* °F)b | Mean Rating Temperature, °F | [LESS THAN ]1 | 1 to [LESS THAN ] 1-1/2 | 1-1/2 to [LESS THAN ] 4 | 4 to [LESS THAN ]8 | [GREATER THAN EQUAL TO] 8 | |
[GREATER THAN EQUAL TO] 350 | 0.32 - 0.34 | 250 | 4.5 | 5.0 | 5.0 | 5.0 | 5.0 |
251 - 350 | 0.29 - 0.32 | 200 | 3.0 | 4.0 | 4.5 | 4.5 | 4.5 |
201 - 250 | 0.27 - 0.30 | 150 | 2.5 | 2.5 | 2.5 | 3.0 | 3.0 |
141 - 200 | 0.25 - 0.29 | 125 | 1.5 | 1.5 | 2.0 | 2.0 | 2.0 |
105 - 140 | 0.21 - 0.28 | 100 | 1.0 | 1.0 | 1.5 | 1.5 | 1.5 |
40 - 60 | 0.21 - 0.27 | 75 | 0.5 | 0.5 | 1.0 | 1.0 | 1.0 |
[LESS THAN ] 40 | 0.20 - 0.26 | 75 | 0.5 | 1.0 | 1.0 | 1.0 | 1.5 |
a For piping smaller than 1-1/2 inch (38 mm) and located in partitions within conditioned spaces, reduction of these thicknesses by 1 inch (25 mm) shall be permitted (before thickness adjustment required in footnote b) but not to a thickness less than 1 inch (25 mm).
b For insulation outside the stated conductivity range, the minimum thickness (T) shall be determined as follows:
c For direct-buried heating and hot water system piping, reduction of these thicknesses by 1-1/2 inches (38 mm) shall be permitted (before thickness adjustment required in footnote b but not to thicknesses less than 1 inch (25 mm).
Wash. Admin. Code § 51-11C-40391