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.

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.

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.

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.

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.

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.

A visual inspection shall confirm that all habitable spaces in the dwelling unit receive space-conditioning system airflow either by use of a ductless space-conditioning system indoor unit located on the wall, ceiling, or floor of the habitable space, or by use of space-conditioning system air supply registers located in the habitable space that use ductwork connected from the register directly to the supply air outlet of a ducted space-conditioning system air handling unit. Refer to Standards Section 100.1 for the definition of habitable space. Transfer fans that move air from one space in the dwelling to a different space in the dwelling, but do not heat or cool the air transferred, do not meet the requirement for providing space-conditioning system airflow.

A visual inspection shall confirm that ductless indoor units are located entirely in conditioned space in accordance with the following requirements:

1. Ductless indoor unit types that mount entirely on the interior surface of dwelling unit walls, ceilings, or floors shall be considered to be entirely in conditioned space. Penetrations in the wall, ceiling or floor surface necessary for the indoor unit refrigerant piping, condensate drain, or electrical connections shall be allowed, provided the penetrations are sealed.
2. Ductless indoor units that penetrate the interior surface of dwelling unit walls, ceilings, or floors, and protrude through cut-out openings in the dwelling unit walls, ceilings, or floors shall be inspected to determine whether the indoor unit is installed inside both the thermal boundary and the air barrier of the dwelling according to the following criteria as applicable:
   1. Ductless indoor units that protrude through the air barrier into unconditioned spaces (including but not limited to attics, crawl spaces, garages, or outdoors) are not located entirely in conditioned space.
   2. Ductless indoor units that protrude into indirectly conditioned spaces (including but not limited to drop ceilings, or floor assemblies in a single family or multifamily multi-story building) that are wholly inside both the thermal boundary and the air barrier of the dwelling are located entirely in conditioned space. Note: Verification at an early stage of building construction may be necessary for visual verification to be possible.

If field verification according to RA3.1.4.1.8 determines the installed system's ductless indoor units are not located entirely in conditioned space, then the system does not comply with the VCHP compliance option eligibility requirements.

Default air handler airflow may be used for any one of the following conditions:

1. for heating-only systems, or
2. when a duct system is being tested prior to installation of the air conditioning or heating system equipment, or
3. when the space conditioning system equipment specification is not known.

Default air handler airflow shall be a calculated value equal to 0.5 CFM per ft² of Conditioned Floor Area.

Nominal air handler airflow shall be calculated according to one of the following methods as applicable:

1. For heating-only systems, the nominal air handler airflow shall be 21.7 CFM per kBtu/hr of rated heating output capacity.
2. For split or packaged cooling systems with only one indoor unit, the nominal air handler airflow shall be 400 CFM per nominal ton of outdoor condensing unit cooling capacity as specified by the manufacturer.
3. For small duct high velocity systems, the nominal air handler airflow shall be 250 CFM per nominal ton of outdoor condensing unit cooling capacity as specified by the manufacturer.
4. For multiple-split systems that provide cooling, the nominal air handler airflow for each indoor unit shall be 350 CFM per nominal ton of indoor unit cooling capacity as specified by the manufacturer.

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.

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:

1. 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.
2. 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.
3. 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.
4. 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.
5. Install a static pressure probe at a supply register located close to the air handler, or at the supply plenum.
6. 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.
7. Record the flow through the flowmeter; this is the leakage flow at 25 Pa (0.1 inches water).
8. 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.

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:

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:

1. 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.
2. 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.
3. Inspect all joints to ensure that no cloth backed rubber adhesive duct tape is used.

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:

1. Seal all the supply registers and return grilles except for one large centrally located return grille or the air handler cabinet access panel.
2. Attach the fan flowmeter device to the duct system at the unsealed return grille or the air handler cabinet access panel.
3. Install a static pressure probe at the supply plenum.
4. 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.
5. 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.
6. 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.
7. Adjust the blower door fan to provide positive 25 Pa (0.1 inches of water) pressure in the conditioned space with respect to outside.
8. 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.
9. 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 required by the Standards, the system passes.
10. 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.

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:

1. Complete the leakage test specified in Section RA3.1.4.3.1 to measure the leakage before commencing duct sealing.
2. Seal all accessible ducts.
3. After sealing is complete, again use the procedure in RA3.1.4.3.1 to measure the leakage after duct sealing.
4. Complete the Smoke Test as specified in RA3.1.4.3.6.
5. Complete the Visual Inspection as specified in RA3.1.4.3.7.

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:

1. 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.
2. Visually inspect all accessible portions of the duct system during smoke injection.
3. 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.

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:

1. Connections to plenums, evaporator coils, and other connections to the forced air unit.
2. Refrigerant lines, p-traps and other penetrations into the forced air unit.
3. Air handler door panel (do not use permanent sealing material, metal tape is acceptable).
4. Register boots sealed to surrounding material at all registers and grilles.
5. Connections between lengths of duct, as well as connections to takeoffs, wyes, tees, and splitter boxes.

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 .

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.