C403.11 Construction of HVAC System Elements (Mandatory)
Supply and return air ducts and plenums shall be insulated with not less than R-6 insulation where located in unconditioned spaces and where located outside the building with not less than R-8 insulation in Climate Zones 1 through 4 and not less than R-12 insulation in Climate Zones 5 through 8. Where located within a building envelope assembly, the duct or plenum shall be separated from the building exterior or unconditioned or exempt spaces by not less than R-8 insulation in Climate Zones 1 through 4 and not less than R-12 insulation in Climate Zones 5 through 8.
Exceptions:
- Where located within equipment.
- Where the design temperature difference between the interior and exterior of the duct or plenum is not greater than 15°F (8°C).
Ducts, air handlers and filter boxes shall be sealed. Joints and seams shall comply with Section 603.9 of the International Mechanical Code.
Longitudinal and transverse joints, seams and connections of supply and return ducts operating at a static pressure less than or equal to 2 inches water gauge (w.g.) (498 Pa) shall be securely fastened and sealed with welds, gaskets, mastics (adhesives), mas-tic-plus-embedded-fabric systems or tapes installed in accordance with the manufacturer's instructions. Pressure classifications specific to the duct system shall be clearly indicated on the construction documents in accordance with the International Mechanical Code.
Exception: Locking-type longitudinal joints and seams, other than the snap-lock and button-lock types, need not be sealed as specified in this section.
Ducts and plenums designed to operate at static pressures equal to or greater than 3 inches water gauge (747 Pa) shall be insulated and sealed in accordance with Section C403.11.1. In addition, ducts and plenums shall be leak tested in accordance with the SMACNA HVAC Air Duct Leakage Test Manual and shown to have a rate of air leakage (CL) less than or equal to 4.0 as determined in accordance with Equation 4-8.
(Equation 4-8)
where:
F = The measured leakage rate in cfm per 100 square feet of duct surface.
P = The static pressure of the test.
Documentation shall be furnished by the designer demonstrating that representative sections totaling not less than 25 percent of the duct area have been tested and that all tested sections comply with the requirements of this section.
Piping serving as part of a heating or cooling system shall be thermally insulated in accordance with Table C403.11.3.
Exceptions:
- Factory-installed piping within HVAC equipment tested and rated in accordance with a test procedure referenced by this code.
- 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 AHRI 840, respectively.
- Piping that conveys fluids that have a design operating temperature range between 60°F (15°C) and 105°F (41°C).
- Piping that conveys fluids that have not been heated or cooled through the use of fossil fuels or electric power.
- Strainers, control valves, and balancing valves associated with piping 1 inch (25 mm) or less in diameter.
- Direct buried piping that conveys fluids at or below 60°F (15°C).
MINIMUM PIPE INSULATION THICKNESS (in inches)a, c
| FLUID OPERATING TEMPERATURE RANGE AND USAGE (°F) | INSULATION CONDUCTIVITY | NOMINAL PIPE OR TUBE SIZE (inches) | |||||
| Conductivity Btu • in./(h • ft2• °F)b | Mean Rating Temperature, °F | < 1 | 1 to < 1 1/2 | 1 1/2 to < 4 | 4 to < 8 | ≥ 8 | |
| > 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 |
| < 40 | 0.20 — 0.26 | 50 | 0.5 | 1.0 | 1.0 | 1.0 | 1.5 |
For SI: 1 inch = 25.4 mm, °C = [(°F) - 32]/1.8.
- For piping smaller than 11/2 inches and located in partitions within conditioned spaces, reduction of these thicknesses by 1 inch shall be permitted (before thickness adjustment required in footnote b) but not to a thickness less than 1 inch.
For insulation outside the stated conductivity range, the minimum thickness (T) shall be determined as follows:
where:
T = minimum insulation thickness,
r = actual outside radius of pipe,
t = insulation thickness listed in the table for applicable fluid temperature and pipe size,
K = conductivity of alternate material at mean rating temperature indicated for the applicable fluid temperature (Btu • in/h • ft2 • °F) and
k = the upper value of the conductivity range listed in the table for the applicable fluid temperature.
- For direct-buried heating and hot water system piping, reduction of these thicknesses by 11/2 inches (38 mm) shall be permitted (before thickness adjustment required in footnote b but not to thicknesses less than 1 inch.