4.5  Pipe and Duct Distribution Systems

4.5.1      Mandatory Measures

4.5.1.1    Requirements for Pipe Insulation

Most piping conveying mechanically heated or chilled fluids for space conditioning or service water heating must be insulated. The required thickness of piping insulation depends on the temperature of the fluid passing through the pipe, the pipe diameter, the function of the pipe within the system, and the insulation’s thermal conductivity.

Table 4-15 specifies the requirements in terms of inches of insulation with conductivity within a specific range. These conductivities are typical for fiberglass or foam pipe insulation. Piping within fan coil units and within other heating or cooling equipment should be insulated based on the pipe diameter and the required value in the table.

Piping that does not require insulation includes the following:

1.   Factory installed piping within space-conditioning equipment certified under §110.1 or §110.2|topic=SECTION 110.2 – MANDATORY REQUIREMENTS FOR SPACE-CONDITIONING EQUIPMENT, see Section 4.2 of this chapter. Nationally recognized certification programs that are accepted by the Energy Commission for certifying efficiencies of appliances and equipment are considered to meet the requirements for this exception.

2.   Piping that conveys fluid with a design operating temperature range between 60 degrees F and 105 degrees F, such as cooling tower piping or piping in water loop heat pump systems.

3.   Where the heat gain or heat loss, to or from piping without insulation, will not increase building source energy use. For example, piping connecting fin-tube radiators within the same space would be exempt, as would liquid piping in a split system air conditioning unit.

This exception would not exempt piping in solar systems. Solar systems typically have backup devices that will operate more frequently if piping losses are not minimized.

4.   Piping that penetrates framing members shall not be required to have pipe insulation for the distance of the framing penetration. Metal piping that penetrates metal framing shall use grommets, plugs, wrapping or other insulating material to assure that no contact is made with the metal framing.

Conductivities and thicknesses listed in Table 4-15 are typical for fiberglass and foam. When insulating materials are used that have conductivities different from those listed here for the applicable fluid range, such as calcium silicate, Equation 4-1 may be used to calculate the required insulation thickness.

When a pipe carries cold fluids, condensation of water vapor within the insulation material may impair the effectiveness of the insulation, particularly for applications in very humid environments or for fluid temperatures below 40 degrees F. Examples include refrigerant suction piping and low-temperature thermal energy storage (TES) systems. In these cases, manufacturers should be consulted, and consideration given to low permeability vapor barriers, or closed-cell foams.

The Energy Code also requires that pipe insulation be protected from damage by moisture, UV and physical abrasion including but not limited to the following:

Insulation exposed to weather shall be installed with a cover suitable for outdoor service. The cover shall be water retardant and provides shielding from solar radiation that can cause degradation of the material. Insulation must be protected by an external covering unless the insulation has been approved for exterior use using a recognized federal test procedure. Adhesive tape shall not be used as protection for insulation exposed to weather.

1.    Insulation covering chilled water piping and refrigerant suction piping located outside the conditioned space shall have a Class I or Class II vapor retarder. All penetrations and joints of which shall be sealed.

2.    Pipe insulation buried below grade must have a waterproof, uncrushable casing or sleeve. The Energy Code does not define “uncrushability” as any material can be crushed, given enough pressure, and thus it is left to the professional judgement of the designer.

If the conductivity of the proposed insulation does not fall into the conductivity range listed in Table 4-15, the minimum thickness must be adjusted using the following equation:

Equation 4-10: Insulation Thickness

Where:

T          = Minimum insulation thickness for material with conductivity K, inches.

PR       = Pipe actual outside radius, inches.

t          = Insulation thickness, inches (Table 4-15 for conductivity k).

K         = Conductivity of alternate material at the mean rating temperature indicated in Table 4-15 for the applicable fluid temperature range, in Btu-in./(h-ft² -°F).

k          = The lower value of the conductivity range listed in Table 4-15 for the applicable fluid temperature, Btu-in/(h-ft² -°F).

Table 4-15a: Space-Heating and Service Water-Heating Systems Pipe Insulation (thickness in inches)
(Steam, Steam Condensate, Refrigerant, Space Heating, Service Hot Water)

Source: Energy Code Table 120.3-A and Table 160.3-D

Table 4-15b: Space-Heating and Service Water-Heating Systems Pipe Insulation (R-Value)
(Steam, Steam Condensate, Refrigerant, Space Heating, Service Hot Water)

Source: Energy Code Table 120.3-A and Table 160.3-D

Table 4-15c: Residential Space-Cooling Systems Pipe Insulation (thickness in inches)
(Chilled Water, Refrigerant and Brine)

Source: Energy Code Table 120.3-A and Table 160.3-D

Table 4-15d: Residential Space-Cooling Systems Pipe Insulation (R-Value)
(Chilled Water, Refrigerant and Brine)

Source: Energy Code Table 120.3-A and Table 160.3-D

Table 4-15e: Nonresidential Space-Cooling Systems Pipe Insulation (thickness in inches)
(Chilled Water, Refrigerant and Brine)

Source: Energy Code Table 120.3-A and Table 160.3-D

Table 4-15f: Nonresidential Space-Cooling Systems Pipe Insulation (R-Value)
(Chilled Water, Refrigerant and Brine)

Source: Energy Code Table 120.3-A and Table 160.3-D

4.5.1.2    Requirements for Air Distribution System Ducts and Plenums

Poorly sealed or poorly insulated duct work can cause substantial losses of air volume and energy. All air distribution system ducts and plenums, including building cavities, mechanical closets, air handler boxes and support platforms used as ducts or plenums, are required to be in accordance with the California Mechanical Code Sections 601, 602, 603, 604, 605 and ANSI/SMACNA-006-2006 HVAC Duct Construction Standards - Metal and Flexible, 3rd Edition

The 2022 Energy Code requires all ductwork to be sealed to meet Seal Class A. Sealing means the use of adhesives, gaskets, and/or tape systems to close openings in the surface of ductwork and field erected plenums and casings through which air leakage would occur, or the use of continuous welds. Seal Class A means sealing all ductwork connections and applicable duct wall penetrations. Penetrations include pipe, tubing, rods, and wire. Rods that penetrate the duct wall must be allowed to move to function properly (such as a control rod for a volume damper) and should not be sealed in a way that prevents operation. Penetrations do not include screws and other fasteners.

Healthcare facilities are exempt from §120.4 and shall comply with the applicable requirements of the California Mechanical Code.

A.  Installation and Insulation

Portions of supply-air and return-air ducts or ductwork conveying heated or cooled air shall be insulated to a minimum installed level of R-8 when installed:

1.   Outdoors

2.   In a space between the roof and an insulated ceiling

3.   In a space directly under a roof with fixed vents or openings to the outside or unconditioned spaces

4.   In an unconditioned crawlspace

5.   In other unconditioned spaces

Portions of supply-air ducts ductwork that are not in one of the above spaces shall be insulated to a minimum installed level of R-4.2 or be exposed in a directly conditioned space. For example, supply-air ducts that are inside the thermal envelope but concealed from view (such as ducts in a chase or above a hard or T-bar ceiling) are required to be insulated with at least R-4.2. However, if the ducts are exposed to directly conditioned space (i.e. ducts are visible to the occupants), then no insulation would be required.

B.  Requirements of the California Mechanical Code

1.   Mechanically fasten connections between metal ducts and the inner core of flexible ducts.

2.   Joint and seal openings with mastic, tape, aerosol sealant or other duct closure system that meets the applicable requirements of UL 181, UL 181A, UL 181B or UL 723 (aerosol sealant).

All joints must be made airtight by use of mastic, tape, aerosol sealant, or other duct-closure system that meets the applicable requirements of UL 181, UL 181A, UL 181B, or UL 723. Duct systems shall not use cloth-back, rubber adhesive duct tape regardless of UL designation, unless it is installed in combination with mastic and clamps.

When mastic or tape is used to seal openings greater than 1/4 inch, a combination of mastic and mesh or mastic and tape must be used.

The Energy Commission has approved two cloth-backed duct tapes with special butyl or synthetic adhesives rather than rubber adhesive to seal flex duct to fittings. These tapes are:

1.  Polyken 558CA or Nashua 558CA, manufactured by Berry Plastics, Tapes and Coatings Division; and

2.  Shurtape PC 858CA, manufactured by Shurtape Technologies, Inc.

These tapes passed Lawrence Berkeley National Laboratory tests comparable to those that cloth-back rubber-adhesive duct tapes failed (the Lawrence Berkeley National Laboratory test procedure has been adopted by the American Society of Testing and Materials as ASTM E2342-03). These tapes are allowed to be used to seal flex ducts to fittings without combination with mastic. These tapes cannot be used to seal other duct system joints, such as the attachment of fittings to plenums and junction boxes. On their backing, these tapes have the phrase "CEC Approved," and a drawing of a fitting to plenum joint in a red circle with a slash through it (the international symbol of prohibition) to illustrate where they are not allowed to be used. Installation instructions in the box explains how to install the tape on duct core to fittings and a statement that the tape cannot be used to seal fitting to plenum and junction box joints.

C.  Factory-Fabricated Duct Systems

Factory-fabricated duct systems must meet the following requirements:

1.   All factory-fabricated duct systems shall comply with UL 181 for ducts and closure systems, including collars, connections, and splices, and be labeled as complying with UL181. UL181 testing may be performed by UL laboratories or a laboratory approved by the Executive Director.

2.   Pressure-sensitive tapes, heat-activated tapes, and mastics used in the manufacture of rigid fiberglass ducts comply with UL 181 and UL181A.

3.   Pressure-sensitive tapes and mastics used with flexible ducts comply with UL181 and UL181B.

4.   All ductwork and plenums with pressure class ratings shall be constructed to Seal Class A. Joints and seams of duct systems and their components shall not be sealed with cloth back rubber adhesive duct tapes unless such tape is used in combination with mastic and drawbands.

Duct located in occupied space and exposed to view is not required to meet Seal Class A.

D.  Field-Fabricated Duct Systems

Field-fabricated duct systems must meet the following requirements:

1.   Factory-made rigid fiberglass and flexible ducts for field-fabricated duct systems comply with UL 181. Pressure-sensitive tapes, mastics, aerosol sealants or other closure systems shall meet applicable requirements of UL 181, UL 181A and UL 181B.

2.   Mastic Sealants and Mesh:

a.    Sealants comply with the applicable requirements of UL 181, UL 181A, and UL 181B, and shall be non-toxic and water resistant.

b.    Sealants for interior applications shall pass ASTM C 731(extrudability after aging) and D 2202 (slump test on vertical surfaces), incorporated herein by reference.

c.     Sealants for exterior applications shall pass ASTM C 731, C 732 (artificial weathering test) and D 2202, incorporated herein by reference.

d.    Sealants and meshes shall be rated for exterior use.

3.   Pressure-sensitive tapes shall comply with the applicable requirements of UL 181, UL 181A and UL 181B.

4.   Drawbands used with flexible duct shall:

a.    Be either stainless-steel worm-drive hose clamps or UV-resistant nylon duct ties.

b.    Have a minimum tensile strength rating of 150 lbs.

c.     Be tightened as recommended by the manufacturer with an adjustable tensioning tool.

5.   Aerosol-Sealant Closures.

a.    Aerosol sealants meet applicable requirements of UL 723 and must be applied according to manufacturer specifications.

b.    Tapes or mastics used in combination with aerosol sealing shall meet the requirements of this section.

6.   All ductwork and plenums with pressure class ratings shall be constructed to Seal Class A. Joints and seams of duct systems and their components shall not be sealed with cloth back rubber adhesive duct tapes unless such tape is used in combination with mastic and drawbands.

Ductwork located in occupied space and exposed to view is not required to meet Seal Class A.

E.  Duct Insulation R-Values

Since 2001, the Energy Code has included the following requirements for the labeling, measurement, and rating of duct insulation:

1.   Insulation R-values shall be based on the insulation only and not include air-films or the R-values of other components of the duct system.

2.   Insulation R-values shall be tested C-values at 75 degrees F mean temperature at the installed thickness, in accordance with ASTM C 518 or ASTM C 177.

3.   The installed thickness of duct insulation for purpose of compliance shall be the nominal thickness for duct board, duct liner, factory made flexible air ducts and factory-made rigid ducts. For factory-made flexible air ducts, the installed thickness shall be determined by dividing the difference between the actual outside diameter and nominal inside diameter by two.

4.   The installed thickness of duct insulation for purpose of compliance shall be 75 percent of its nominal thickness for duct wrap.

5.   Insulated flexible air ducts must bear labels no further than three feet apart that state the installed R-value (as determined per the requirements of the Energy Code).

A typical duct wrap, nominal 1-1/2 inches and 0.75 pound per cubic foot will have an installed rating of R-4.2 with 25 percent compression.

F.   Protection of duct Insulation

The Energy Code requires that exposed duct insulation be protected from damage by moisture, UV and physical abrasion including but not limited to the following:

1.   Insulation exposed to weather shall be suitable for outdoor service, e.g., protected by aluminum, sheet metal, painted canvas, or plastic cover. Insulation must be protected by an external covering unless the insulation has been approved for exterior use using a recognized federal test procedure.

2.   Cellular foam insulation shall be protected as above or painted with a coating that is water retardant and provides shielding from solar radiation that can cause degradation of the material.

G     Duct Sealing and Leakage Testing.

Since 2001, the Energy Code has included prescriptive duct leakage testing for ducts that are part of small single zone systems with portions of the ductwork either outdoors or in uninsulated or vented ceiling spaces. The 2019 California Mechanical Code (CMC) introduced mandatory requirements to seal and test all nonresidential air distribution systems. The prescriptive requirements for duct leakage in the Energy Code were therefore made mandatory and all systems that do not meet the criteria for testing according to the Energy Code are required to meet the requirements in the CMC.

New or replacement duct systems that meet the criteria in 1-4 below shall be sealed to a leakage rate not to exceed 6 percent of the nominal air handler airflow rate as confirmed through HERS field verification and diagnostic testing, in accordance with Reference Nonresidential Appendix NA7.5.3.

1.    The duct system does not serve a healthcare facility.

2.    The duct system provides conditioned air to an occupiable space for a constant volume, single zone, space-conditioning system.

3.    The space conditioning system serves less than 5,000 square feet of conditioned floor area.

4.    The combined surface area of the ducts located outdoors or in unconditioned space is more than 25 percent of the total surface area of the entire duct system.

New or replacement duct systems that do not meet the criteria above shall instead meet the duct leakage testing requirements of CMC Section 603.10.1.

Alterations to an existing space conditioning system may trigger the duct sealing requirement. For more information, see Section 4.10.4.2.

A.    Duct Leakage Testing for Multiple Duct Systems with Common Return Ducts

If there are two or more duct systems in a building that are tied together at a common return duct, then each duct system should be tested separately, including the shared portion of the return duct system which should be included in each system test. Under this scenario, the portions of the second duct system that is not being tested must be completely isolated from the portions of the ducts that are being tested, so the leakage from the second duct system does not affect the leakage rate from the side that is being tested. The diagram below represents the systems that are attached to a shared return boot or remote return plenum. In this case, the point in the return system that needs to be blocked off is readily accessible through the return grille. The “duct leakage averaging” method where both systems are tested together (as though it is one large system) and the results divided by the combined tonnage to get the target leakage may not be used as it allows a duct system with more the 6 percent leakage to pass if the combined system’s leakage is 6 percent or less.

Figure 4-13: Example of Two Duct Systems with a Common Return

H             Acceptance Requirements

The Energy Code has acceptance requirements where duct sealing and leakage testing is required by §120.5(a)3.

These tests are described in the Chapter 13, Acceptance Requirements, and the Reference Nonresidential Appendix NA7|topic=Appendix NA7 – Installation and Acceptance Requirements for Nonresidential Buildings and Covered Processes.