## RA3.1 Field Verification and Diagnostic Testing of Air Distribution Systems

### RA3.1.1 Purpose and Scope

RA3.1 contains procedures for measuring the air leakage in forced air distribution systems as well as procedures for verifying duct location, duct surface area, duct R-value, return duct design, return grille design, and air filter installation.

RA3.1 applies to air distribution systems in both new and existing low-rise residential buildings.

RA3.1 provides required procedures for installers, HERS raters and others who need to perform field verification of air distribution systems.

Table RA3.1-1 is a summary of the tests and criteria included in RA3.1.

Table RA3.1-2 Provides compliance criteria for the duct leakage test protocols in Section RA3.1.4.3.

#### Table RA3.1-1 – Summary of Duct System Field Verification and Diagnostic Test Protocols

Verification/Diagnostic | Description | Procedure
Duct Location, Surface Area and R-value | Verify duct system was installed according to the specifications on the Certificate of Compliance or in accordance with an approved duct system design layout. | RA3.1.4.1
Verified Duct System Design | Procedure for duct system design layout approval and field verification | RA3.1.4.1.1
Duct Leakage | Verify that duct leakage is less than or equal to the compliance criteria given in Table RA3.1-2. | RA3.1.4.3
Return Duct Design | Verify compliance with the return duct and return grill sizing requirements of Table 150.0-B or Table 150.0-C. | RA3.1.4.4
Air Filter Device Design | Verify compliance with the requirements in 150.0(m)12. | RA3.1.4.5
Verification of Prescriptive Bypass Duct Requirements | Verification to confirm zonally controlled systems comply with the bypass duct requirements in 150.1(c)13 | RA3.1.4.6

### RA3.1.2 Instrumentation Specifications

The instrumentation for the air distribution diagnostic measurements shall conform to the following specifications:

RA3.1.2.1 Pressure Measurements

All pressure measurements shall be measured with measurement systems (i.e. sensor plus data acquisition system) having an accuracy equal to or better than ± 1% of pressure reading or ± 0.2 Pa. (0.0008 inches water) (whichever is greater). All pressure measurements within the duct system shall be made with static pressure probes such as Dwyer A303 or equivalent.

RA3.1.2.2 Duct Leakage Measurements

Duct leakage airflow rates during duct leakage testing shall be measured with a duct leakage airflow rate measurement apparatus that has a duct leakage airflow rate measurement accuracy equal to or better than ± 3 percent of reading or ± 1 cfm (whichever is greater).

RA3.1.2.3 Calibration

All instrumentation used for duct leakage diagnostic measurements shall be calibrated according to the manufacturer’s calibration procedure to conform to the accuracy requirement specified in Section RA3.1.2.

### RA3.1.3 Diagnostic Apparatus

RA3.1.3.1 Apparatus for Duct Pressurization and Leakage Flow Measurement

The apparatus for fan pressurization duct leakage measurements shall consist of a duct pressurization and flow measurement device meeting the specifications in Section RA3.1.2.

RA3.1.3.2 Apparatus for Duct Leakage to Outside Measurement

The apparatus for measuring duct leakage to outside shall include a fan that is capable of maintaining the pressure within the conditioned spaces in the house at 25 Pa (0.1 inches water) relative to the outdoors. The fan most commonly used for this purpose is known as a “blower door” and is typically installed within a temporary seal of an open exterior doorway.

RA3.1.3.3 Apparatus for Smoke-Test of Accessible-Duct Sealing (Existing Duct Systems)

The apparatus for determining leakage in and verifying sealing of all accessible leaks in existing duct systems provide means for introducing controllable amounts of non-toxic visual/theatrical smoke into the duct pressurization apparatus for identifying leaks in accessible portions of the duct system. The means for generating smoke shall have sufficient capacity to ensure that any accessible leaks will emit visibly identifiable smoke.

### RA3.1.4 Verification and Diagnostic Procedures

This section describes the procedures used to verify compliance with the mandatory and performance compliance requirements for air distribution systems.

RA3.1.4.1 Diagnostic Duct Location, Surface Area and R-value

The performance compliance calculations allow credit for duct systems that are designed to be in advantageous locations, that have reduced duct surface areas, and/or that provide higher R-values or portions of the system. This section specifies procedures for verification of duct systems for conformance with the requirements for the performance compliance credits. When indicated on the Certificate of Compliance, the Installer shall certify compliance with the applicable procedures in RA3.1.4.1 on a Certificate of Installation, and a HERS rater shall verify compliance on a Certificate of Verification.

##### RA3.1.4.1.1 Verified Duct System Design

An installed duct system meets the Verified Duct System Design compliance criteria if it is field verified by a HERS rater to be in conformance with a duct design layout that meets all applicable duct design and documentation requirements given in Section RA3.1.4.1.1. The duct design layout shall be approved by the enforcement agency.

RA3.1.4.1.1.1 Verified Duct System Design - Duct Design Layout

The duct system design shall be documented on the Duct Design Layout, a scaled layout drawing that identifies the location of the space conditioning equipment, all supply and return registers/grilles, the size, R-value, and location of each duct segment. The Duct Design Layout shall incorporate all other duct details reported on the registered Certificate of Compliance.

RA3.1.4.1.1.2 Verified Duct System Design - Compliance Criteria

The duct system design shall be based on an industry standard design methodology such as ACCA Manual D or an equivalent, and shall take into account: the available external static pressure from the air handler, the equivalent length or pressure drop of external devices, and the pressure drop of the duct runs accounting for size, type and configuration of the ducts and fittings. The duct system shall be designed to meet the required system airflow rate with the manufacturer-specified available external static pressure for the specified system air handler at that airflow. The duct system design shall include calculations that indicate the duct system will operate at equal to or greater than 0.0292 cfm/Btu (350 cfm/12000 Btu) in cooling speed (350 cfm per nominal ton of condensing unit cooling capacity specified by the manufacturer) or, if heating only, equal to or greater than 16.8 cfm per 1000 Btu/hr furnace nominal output specified by the manufacturer.

RA3.1.4.1.1.3 Verified Duct System Design - Duct Design Layout Approval

The Duct Design Layout shall be included with the building design plans and the registered 3 Certificate of Compliance submitted to the enforcement agency in conjunction with the application for the building permit. A copy of the Duct Design Layout approved by the enforcement agency shall be posted or made available with the building permit(s) issued for the building, and shall be made available to the enforcement agency, installing contractor, and HERS rater for use during the installation work and for all applicable inspections.

RA3.1.4.1.1.4 Verified Duct System Design - Field Verification of Installation

The location of all supply and return registers shall be verified by inspection of the interior of the dwelling unit. The location of the space conditioning equipment and the size, R-value, and location of each duct segment shall be verified by observation in the spaces where they are located. Deviations from the approved Duct Design Layout shall not be allowed without a revised a Duct Design Layout approved by the enforcement agency.

##### RA3.1.4.1.2 Verification of 12 Linear Feet or Less of Duct Located Outside Of Conditioned Space

A visual inspection shall confirm space conditioning systems with air handlers located outside the conditioned space have 12 linear feet or less of duct located outside the conditioned space including air handler and plenum. If the space conditioning system has more than 12 feet of duct outside of conditioned space, the system does not pass.

##### RA3.1.4.1.3 Visual Verification of Ducts Located Entirely In Conditioned Space

A visual inspection shall confirm space conditioning duct systems are located entirely in conditioned space. If any part of the space conditioning duct system is outside of conditioned space, the system does not pass.

##### RA3.1.4.1.4 Verification of Duct Surface Area Reduction

Compliance with Verified Duct System Design procedures specified in RA3.1.4.1.1 are prerequisite for compliance with the Duct Surface Area Reduction compliance credit. A visual inspection shall on confirm the installed duct system layout conforms to the Duct Design Layout.

##### RA3.1.4.1.5 Verification of Buried Ducts on The Ceiling R-Value

Compliance with Verified Duct System Design procedures specified in RA3.1.4.1.1 is prerequisite for compliance with the Buried Ducts on the Ceiling compliance credit. A visual inspection shall confirm the installed duct system layout conforms to the Duct Design Layout. This procedure shall be carried out prior to covering the ducts with insulation.

Ducts designed to be buried shall be insulated to R4.2 or greater. In addition, ducts designed to be in contact with the ceiling shall be not more than 3.5 inches from the ceiling drywall. A sign shall be hung near the attic access that displays a warning: “Caution: Buried Ducts. Markers indicate location of buried ducts.” All ducts that will be completely buried shall have vertical markers that are visible after insulation installation, placed at least every 8 feet of duct length and at the beginning and end of each duct run.

##### RA3.1.4.1.6 Verification of Deeply Buried Ducts R-Value

Compliance with Verified Duct System Design procedures specified in RA3.1.4.1.1 is prerequisite for compliance with the Deeply Buried Ducts compliance credit. A visual inspection shall confirm the installed duct system layout conforms to the Duct Design Layout. This procedure shall be carried out prior to covering the ducts with insulation.

Ducts designed to be buried shall be insulated to R4.2 or greater. In addition, ducts designed to be in contact with the ceiling shall be not more than 3.5 inches from the ceiling drywall. A sign shall be hung near the attic access that displays a warning: “Caution: Buried Ducts. Markers indicate location of buried ducts.” All ducts that will be completely buried shall have vertical markers that are visible after insulation installation, placed at least every 8 feet of duct length and at the beginning and end of each duct run.

RA3.1.4.2 Determining Air Handler Airflow for Calculation of Duct Leakage Rate Compliance Targets

For use in establishing the target duct leakage rate compliance criteria, the system air handler airflow shall be calculated using RA3.1.4.2.1, RA3.1.4.2.2, or RA3.1.4.2.3

##### RA3.1.4.2.1 Default Air Handler Airflow

Default air handler airflow may be used only for homes where the duct system is being tested before the air conditioning and heating system is installed and the equipment specification is not known. For heating only systems the default air handler airflow shall be 0.5 CFM per ft² of Conditioned Floor Area.

##### RA3.1.4.2.2 Nominal Air Handler Airflow

For heating only systems the nominal air handler airflow shall be 21.7 CFM per kBtu/hr of rated heating output capacity. For split or packaged systems with cooling, the nominal air handler airflow shall be 400 CFM per nominal ton of condensing unit cooling capacity as specified by the manufacturer or the heating only value, whichever is greater. For small duct high velocity systems, the nominal air handler airflow shall be 250 CFM per nominal ton of condensing unit cooling capacity as specified by the manufacturer.

##### RA3.1.4.2.3 Measured System Airflow

The system airflow shall be as measured according to a procedure in Section RA3.3.3. The system airflow can be used as the air handler airflow for the purpose of establishing duct leakage percentage.

RA3.1.4.3 Diagnostic Duct Leakage

Diagnostic duct leakage measurement is used by installers and raters to verify that total leakage meets the criteria for any sealed duct system specified in the compliance documents. Table RA3.1-2 summarizes the leakage test procedures that may be used to demonstrate compliance.

#### Table RA3.1-2 – Duct Leakage Verification and
Diagnostic Test Protocols and Compliance Criteria

Verification Description | User Application | Procedure(s)
Sealed and tested new duct systems in single family homes and townhomes | Installer Testing at Final HERS Rater Testing | RA3.1.4.3.1
Sealed and tested new duct systems in single family homes and townhomes | Installer Testing at Rough-in, Air Handling Unit Installed | RA3.1.4.3.2 RA3.1.4.3.2.1 RA3.1.4.3.3
Sealed and tested new duct systems in single family homes and townhomes | Installer Testing at Rough-in, Air Handling Unit Not Installed | RA3.1.4.3.2 RA3.1.4.3.2.2|topic=RA3.1.4.3.2.2 Ducts with Air Handling Unit Not Yet Installed\ RA3.1.4.3.3
Sealed and tested new duct systems in multifamily homes regardless of duct system location. | Installer Testing at Final HERS Rater Testing | RA3.1.4.3.1
Sealed and tested new duct systems in multifamily homes regardless of duct system location. | Installer Testing at Final HERS Rater Testing | RA3.1.4.3.4
Verification of Low Leakage Air Handler with Sealed and Tested Duct System Compliance Credit | Installer Testing at Final HERS Rater Testing | RA3.1.4.3.1 and RA3.1.4.3.9
Verification of low leakage ducts located entirely in conditioned space. | Installer Testing HERS Rater Testing | RA3.1.4.3.8
Sealed and tested altered existing duct systems | Installer Testing HERS Rater Testing | RA3.1.4.3.1
Sealed and tested altered existing duct systems | Installer Testing HERS Rater Testing | RA3.1.4.3.4
Sealed and tested altered existing duct systems | Installer Testing and Inspection HERS Rater Testing and Verification | RA3.1.4.3.5 RA3.1.4.3.6 RA3.1.4.3.7

##### RA3.1.4.3.1 Diagnostic Duct Leakage from Fan Pressurization of Ducts

The objective of this procedure is for an installer to determine or a rater to verify the total leakage of a new or altered duct system. The total duct leakage shall be determined by pressurizing the entire duct system to a positive pressure of 25 Pa (0.1 inches water) with respect to outside. The following procedure shall be used for the fan pressurization tests:

(a) Verify that the air handler, supply and return plenums and all the connectors, transition pieces, duct boots and registers are installed and sealed. The entire duct system shall be included in the total leakage test.

(b) For newly installed or altered ducts, verify that cloth backed rubber adhesive duct tape has not been used and if a platform or other building cavity used to house the air distribution system has been newly installed or altered, it contains a duct or is ducted with duct board or sheet metal.

(c) Seal all the supply registers and return grilles except for one large centrally located return grille or the air handler cabinet access panel. Floor registers on carpeted floors may be removed and the opening sealed to the floor under the carpet. If allowed by the equipment manufacturer, the air-handling unit blower compartment access panel may be sealed with an approved tape - do not use mastic or other permanent sealing material.

(d) Attach the fan flowmeter device to the duct system at the unsealed return grille or the air handler cabinet access panel. Ensure that the air filter has been removed.

(e) Install a static pressure probe at a supply register located close to the air handler, or at the supply plenum.

(f) Adjust the fan flowmeter to produce a positive 25 Pa (0.1 inches water) pressure at the supply register or the supply plenum with respect to the outside or with respect to the building space with the entry door open to the outside.

(g) Record the flow through the flowmeter; this is the leakage flow at 25 Pa (0.1 inches water).

(h) Divide the leakage flow by the total air handler airflow determined by the procedure in Section RA3.1.4.2 and convert to a percentage. If the leakage flow percentage is equal to or less than the compliance criterion required by the Standards, the system passes.

##### RA3.1.4.3.2 Diagnostic Duct Leakage at Rough-in Construction Stage

Installers may determine duct leakage in newly constructed buildings by using diagnostic measurements at the rough-in building construction stage prior to installation of the interior finishing. When using this measurement technique, the installer shall complete additional inspection (as described in section RA3.1.4.3.3) of duct integrity after the finishing wall has been installed. In addition, after the finishing wall is installed, spaces between the register boots and the wallboard shall be sealed. Cloth backed rubber adhesive duct tapes shall not be used to seal the space between the register boot and the wall board.

The duct leakage measurement at rough-in construction stage shall be performed using a fan pressurization device. The duct leakage shall be determined by pressurizing both the supply and return ducts to 25 Pa (0.1 inches water). The following procedure (either RA3.1.4.3.2.1 or RA3.1.4.3.2.2) shall be used:

RA3.1.4.3.2.1 Ducts with the Air Handling Unit Installed and Connected:

For total leakage:

(a) Verify that supply and return plenums and all the collars, connectors, transition pieces, duct boots, and return boxes have been installed. If a platform or other building cavity is used to house portions of the air distribution system, it shall contain a duct, be lined with duct board or sheet metal, and all duct connectors and transition parts shall be installed and sealed. The platform, ducts, and connectors shall be included in the total leakage test. All joints shall be inspected to ensure that no cloth backed rubber adhesive duct tape is used.

(b) Seal all the supply duct boots and return boxes except for one return duct box.

(c) Attach the fan flowmeter device at the unsealed return duct box.

(d) Insert a static pressure probe at one of the sealed supply duct boots located close to the supply plenum or at the supply plenum.

(e) Adjust the fan flowmeter to maintain a positive 25 Pa (0.1 inches water) pressure in the duct system with respect to the outside, or with respect to the building space with the entry door open to the outside.

(f) Record the flow through the flowmeter; this is the leakage flow at 25 Pa (0.1 inches water).

(g) Divide the leakage flow by the total air handler airflow determined by the procedure in Section RA3.1.4.2 and convert to a percentage. If the leakage flow percentage is less than or equal to the compliance criterion required by the Standards the system passes.

RA3.1.4.3.2.2 Ducts with Air Handling Unit Not Yet Installed:

For total leakage:

(a) Verify that supply and return plenums and all the collars, connectors, transition pieces, duct boots, and return boxes have been installed. If a platform or other building cavity is used to house portions of the air distribution system, it shall contain a duct, be lined with duct board or sheet metal, and all duct connectors and transition parts shall be installed and sealed. The platform, ducts and connectors shall be included in the total leakage test. All joints shall be inspected to ensure that no cloth backed rubber adhesive duct tape is used.

(b) Supply and return leaks may be tested separately, or the supply and return plenums may be connected together using suitable temporary air-tight means to facilitate testing the total system. If the supply and return systems are to be tested separately, the opening to the supply or return plenums shall be sealed to prevent leakage unless used as the point of attachment for the fan flowmeter.

(c) Seal all the supply duct boots and/or return duct boxes except for a location where the fan flowmeter device will be attached.

(d) Attach the fan flowmeter device at the unsealed location.

(e) Insert a static pressure probe at one of the sealed supply duct boots, or return duct boxes, located at a point in the system close to the fan flowmeter.

(f) Adjust the fan flowmeter to produce a positive 25 Pa (0.1 inches water) pressure at the supply plenum with respect to the outside or with respect to the building space with the entry door open to the outside.

(g) Record the airflow through the flowmeter; this is the leakage flow at 25 Pa (0.1 inches water).

(h) If the supply and return ducts are tested separately, repeat items 4 through 6 with the flow meter attached to the unsealed return box and the static pressure probe in the return duct boxes, located at a point in the system close to the fan flowmeter, then add the two leakage rates together to get a total leakage flow.

(i) Divide the leakage flow by the total air handler airflow determined by the procedure in Section RA3.1.4.2 and convert to a percentage. If the leakage flow percentage is less than or equal to the compliance criterionrequired by the Standards, the system passes.

##### RA3.1.4.3.3 Installer Visual Inspection at Final Construction Stage

After installing the interior finishing drywall, or other finishing material, and verifying that one of the above rough-in tests was completed, the following procedure shall be used:

(a) Remove at least one supply and one return register, and verify that the spaces between the register boot and the interior finishing wall are properly sealed.

(b) If the house rough-in duct leakage test was conducted without an air handler installed, inspect the connection points between the air handler and the supply and return plenums to verify that the connection points are properly sealed.

(c) Inspect all joints to ensure that no cloth backed rubber adhesive duct tape is used.

##### RA3.1.4.3.4 Duct Leakage to Outside from Fan Pressurization of Ducts

The objective of this test is to determine the amount of duct leakage to outside the air barrier for the conditioned space. This measurement is utilized to verify that duct systems are located entirely within conditioned space. The procedure is also utilized to provide an alternate leakage measurement for situations when it is likely that a portion of the total duct leakage is inside the air barrier for the conditioned space. The duct leakage to outside shall be determined by pressurizing the ducts and the conditioned space of the house to 25 Pa (0.1 inches water) with respect to outside. The following procedure shall be used for the fan pressurization test of leakage to outside:

(a) Seal all the supply registers and return grilles except for one large centrally located return grille or the air handler cabinet access panel.

(b) Attach the fan flowmeter device to the duct system at the unsealed return grille or the air handler cabinet access panel.

(c) Install a static pressure probe at the supply plenum.

(d) Attach a blower door to an external doorway. If the door between the dwelling and the garage is used, the garage car-bay doors must be open.

(e) If any ducts are located in an unconditioned basement, all doors or accesses between the conditioned space and the basement shall be closed, and at least one operable door or window (if it exists) between the basement and outside shall be open during the test.

(f) If the ducts are located in a conditioned basement, any door between the basement and the remaining conditioned space shall be open, and any basement doors or windows to outside must be closed during the test.

(g) Adjust the blower door fan to provide positive 25 Pa (0.1 inches of water) pressure in the conditioned space with respect to outside.

(h) Adjust the fan/flowmeter to maintain a zero pressure difference (plus or minus 0.5Pa (.002 inches water)) between the ducts and the conditioned space, and adjust the blower door fan to maintain a positive 25 Pa (0.1 inches of water) pressure in the conditioned space with respect to outside. This step may require several iterations.

(i) Record the flow through the flowmeter; this is the duct leakage flow to outside at 25 Pa (0.1 inches water). If the leakage flow is less than or equal to the applicable compliance criteria in Table RA3.1-2, required by the Standards, the system passes.

(j) If required for compliance, divide the leakage flow by the system air handler airflow determined by the procedure in Section RA3.1.4.2, and convert to a percentage. If the leakage flow percentage is less than or equal to the criterion required by the Standards, the system passes.

##### RA3.1.4.3.5 Sealing of All Accessible Leaks

For altered existing duct systems that are unable to pass either the Fan Pressurization of Ducts test (RA3.1.4.3.1), or the Duct Leakage to Outside test (RA3.1.4.3.4), the objective of this test is to verify that all accessible leaks are sealed. The following procedure shall be used:

(a) Complete the leakage test specified in Section RA3.1.4.3.1 to measure the leakage before commencing duct sealing.

(b) Seal all accessible ducts.

(c) After sealing is complete, again use the procedure in RA3.1.4.3.1 to measure the leakage after duct sealing.

(d) Complete the Smoke Test as specified in RA3.1.4.3.6.

(e) Complete the Visual Inspection as specified in RA3.1.4.3.7.

##### RA3.1.4.3.6 Smoke-Test of Accessible-Duct Sealing

For altered existing ducts that fail the leakage tests, the objective of the smoke test is to confirm that all accessible leaks have been sealed. The following procedure shall be used:

(a) Inject either theatrical or other non-toxic smoke into a fan pressurization device that is maintaining a duct pressure difference of 25 Pa (0.1 inches water) relative to the duct surroundings, with all grilles and registers in the duct system sealed.

(b) Visually inspect all accessible portions of the duct system during smoke injection.

(c) The system shall pass the test if one of the following conditions is met:

1. No visible smoke exits the accessible portions of the duct system.

2. Smoke only emanates from the furnace cabinet which is gasketed and sealed by the manufacturer and no visible smoke exits from the accessible portions of the duct system.

##### RA3.1.4.3.7 Visual Inspection of Accessible Duct Sealing

The objective of this inspection in conjunction with the smoke test (RA3.1.4.3.6) is to confirm that all accessible leaks have been sealed. Visually inspect to verify that the following locations have been sealed:

(a) Connections to plenums, evaporator coils, and other connections to the forced air unit

(b) Refrigerant lines, p-traps and other penetrations into the forced air unit

(c) Air handler door panel (do not use permanent sealing material, metal tape is acceptable)

(d) Register boots sealed to surrounding material at all registers and grilles,

(e) Connections between lengths of duct, as well as connections to takeoffs, wyes, tees, and splitter boxes.

##### RA3.1.4.3.8 Verification of Low Leakage Ducts Located Entirely In Conditioned Space

A visual inspection shall confirm the duct system location as specified by Section RA3.1.4.1.3. Additionally, ducts shall be confirmed to have less than or equal to 25 cfm leakage to outside when measured as specified by Section RA3.1.4.3.4.

##### RA3.1.4.3.9 Verification of Low Leakage Air-Handling Unit with Sealed and Tested Duct System

An additional performance compliance credit is available for verified low leakage ducts if a qualified low leakage air-handling unit is installed. The low leakage air-handling unit cabinet (furnace, or heat pump fan and inside coil) shall conform to the qualification requirements given in Reference Joint Appendix JA9, and shall be included in the list of low leakage air handling units published by the Energy Commission. The qualified air handler must be connected to a sealed and tested new duct system to receive the credit.

In order to comply with this credit, the duct system shall be verified to leak less than or equal to the leakage rate specified on the Certificate of Compliance using the methods in Section RA3.1.4.3.1, and the air handler manufacturer make and model number shall be verified to be a model certified to the Energy Commission as qualified for credit as a low leakage air handler.

RA3.1.4.4 Verification of Return Duct Design

Verification shall consist of a visual inspection to confirm that the duct design conforms to the criteria given in Table 150.0-B or Table 150.0-C.

RA3.1.4.5 Verification of Air Filter Device Design

Verification shall consist of a visual inspection to confirm that the air filter devices conform to the requirements given in Section 150.0(m)12.

RA3.1.4.6 Verification of Bypass Ducts for Zonally Controlled Forced Air Systems

When a zonally controlled forced air system is installed, a visual inspection shall confirm:

(a) That bypass ducts are not used to deliver conditioned supply air directly to the space conditioning system return duct airflow; or

(b) That the Certificate of Compliance indicates an allowance for use of bypass ducts.