13.61 Test Procedure: NA7.5.3 Air Distribution Systems Acceptance, Use Form NRCA-MCH-04-A

This test only applies to single-zone units serving less than 5,000 ft² of floor area where 25 percent or more of the duct surface area is in one of the following spaces:

• In a space directly under a roof where the U-factor of the roof is greater than the U-factor of the ceiling, or

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

Within this criteria, this test applies to both new duct systems and to existing duct systems which are either being extended per §141.0(b)2D or the space conditioning system is altered by the installation or replacement of space conditioning equipment per §141.0(b)2E, including: replacement of the air handler; outdoor condensing unit of a split system air conditioner or heat pump; cooling or heating coil; or the furnace heat exchanger. Existing duct systems do not have to be tested if they are insulated or sealed with asbestos.

The duct work of these small single-zone systems with ducts in unconditioned spaces must meet the duct leakage requirements of §140.4(l) for new ducts or §141.0(b)2D for existing ducts. However only new duct systems or the extension of existing ducts must meet the requirements of §120.4, including construction materials, installation, and insulation R-values. Existing ducts are not required to be brought up to current Standards in terms of insulation, or requirements for joint seams and fasteners.

The first component of the construction inspection is to assure that the duct system falls under the scope this test (see above Scope of the Requirements). The rest of the construction inspections apply to new duct systems or extensions of existing ducts only.

Perform a brief review of the drawings and construction to verify that the following items are specified in the construction set and installed in the field. A comprehensive review of each duct is not required.

Drawbands are either stainless steel worm-drive hose clamps or UV-resistant nylon duct ties. Verify compliance by reviewing material cut sheets and visual inspection.

Flexible ducts are not constricted in any way. For example, ensure the flex duct is not compressed against immovable objects, squeezed through openings, or contorted into extreme configurations (i.e., 180° angles). Flex duct that is constricted can increase system static pressure as well as compromise insulation values. Verify compliance through visual inspection.

Duct inspection and leakage tests shall be performed before access to ductwork and associated connections are blocked by permanently installed construction material. The intent here is to ensure construction modifications can be made, if necessary, before access to the ductwork is restricted.

Joints and seams are not sealed with a cloth-back rubber adhesive tape unless used in combination with mastic and drawbands. Verify compliance through visual inspection.

Duct R-values are verified. Duct insulation R-value shall comply with §120.4(a), §120.4(c), and §120.4(d), and can be verified by reviewing material cut sheets and through visual inspection.

Insulation is protected from damage, or suitable for outdoor usage, per §120.4(f). Verify compliance by reviewing material cut sheets and through visual inspection.

Refer to the Scope of the Requirements section above to determine when this test is required. When required, the test will often be conducted by the installer and verified by a HERS rater using the procedures outlined in Reference Nonresidential Appendix NA2, and documented on compliance form, NRCA-MCH-04-A.

The primary metric calculated is the leakage fraction of total fan flow. Total fan flow is based on the cooling capacity of heating and cooling equipment and based on the heating capacity of heating only equipment. As described in Reference Nonresidential Appendix NA2.1.4.1, total fan flow is determined to be 400 cfm/ton for cooling or heating/cooling equipment where a ton of cooling capacity is equal to 12 kBtu/h of cooling capacity. For heating only equipment, total fan flow is 21.7 cfm per kBtuh rated output capacity. The cooling and heating capacity of equipment can be found on the product nameplate.

For new duct systems, the installer blocks off all of the supply and return registers or diffusers and pressurize the ducts with a fan flowmeter to 25 Pascals (Pa) and records the leakage airflow measured by the fan flowmeter. This leakage amount at 25 Pa is divided by the total fan flow to generate the leakage percentage value. If this leakage percentage is less than or equal to 6 percent, the system passes. If the system does not pass, then the installer should look locate and seal any leaks/gaps until the system conforms to the maximum 6 percent leakage requirement. It is easier to find leaks with the ducts pressurized as one can often feel the air escaping from larger leaks/gaps.

For existing duct systems that are having additional ducts added or are having major repairs or replacement of equipment connected to the ducts, the leakage rate of the existing duct system should be tested first before any alterations proceed. This leakage amount is the Pre-test leakage value. After the additional ducts or equipment repairs or replacements conducted, then the ducts are sealed along any fittings or joints. After blocking off all supply and return registers or diffusers, the ducts are then pressurized using a fan flowmeter to 25 Pascals (Pa) and the fan flowmeter measures the final test leakage rate at 25 Pa. This final test leakage amount at 25 Pa is divided by the total fan flow to generate the leakage percentage value. If this leakage percentage is less than or equal to 15 percent, the system passes. If the system does not pass, then the installer should locate and seal any accessible leaks/gaps. It is easier to find leaks with the ducts pressurized as one can often feel the air escaping from larger leaks/gaps.

If after all accessible leaks are sealed, the leakage percentage is still above 15 percent, the installer has two options:

• If the final test leakage is 60 percent lower than the pre-test leakage rate and a visual inspection finds no accessible leaks, crushed ducts, animal infestation, rusted ducts etc., this will be sufficient to pass this requirement.

• If the system meets neither the 15 percent leakage percentage nor was it possible to reduce the pre-tested leakage value by 60 percent, then the system must pass a visual inspection by a HERS rater. Unlike the other methods of compliance this method cannot be sampled – every system must be inspected by the HERS rater.

After completing the air distribution system acceptance test, the installer shall affix a sticker to the air handler access door describing if the system met the prescriptive leakage requirements (6 percent leakage for new systems and 15 percent for existing systems) or if the system failed to meet this standard but that all accessible leaks were sealed. The installer supplies the stickers and can have their company logo on them. However, the preceding information must be on the sticker in 14 point font or larger.

After conducting the air distribution system acceptance test, the installer or the permit applicant must arrange to have a HERS rater perform the required third party verification. Copies of the Construction Inspection and the Air Distribution System Leakage Diagnostic sections of the NRCA-MCH-04-A should be sent to the HERS Provider, HERS rater; the Builder (General Contractor or Construction Manager), the Building Owner at Occupancy and a copy must be posted at the construction site and made available for all applicable inspections by the enforcement agency.

The HERS rater must perform field verification and diagnostic testing, document the results on a Certificate of Field Verification and Diagnostic Testing, and send copies of the Certificate of Field Verification and Diagnostic Testing to the Builder (General Contractor or Construction Manager), the Building Owner at Occupancy, and a copy must be posted at the construction site and made available for all applicable inspections by the enforcement agency. If the test complies by virtue of the tested leakage (6 percent for new ducts and 15 percent for existing duct) or by virtue of a 60 percent leakage reduction after the system was repaired or altered, the building permit applicant may choose for the HERS field verification to be completed for the permitted space conditioning unit alone, or alternatively as part of a designated sample group of up to seven space conditioning units for which the same installing company has completed work that requires field verification and diagnostic testing for compliance. If the sampling method is chosen, the HERS rater must randomly select one system from the group for verification. For existing duct systems that fail both the 15 percent leakage rate and the 60 percent reduction in leakage, the HERS rater must validate all of these systems (100 percent sampling) by visual inspection. Refer to Nonresidential Appendix NA1.5 for additional information about sampling.

Below are excerpts of air distribution system acceptance testing requirements from Reference Nonresidential Appendix NA2.1 Procedures for Field Verification and Diagnostic Testing of Air Distribution Systems.

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

All pressure measurements shall be measured with measurement systems (i.e. sensor plus data acquisition system) having an accuracy of ± 0.2 Pa. All pressure measurements within the duct system shall be made with static pressure probes, Dwyer A303 or equivalent.

Duct leakage air flows during duct leakage testing shall be measured with digital gauges that have an accuracy of ± 3 percent or better.

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 NA2. All testers performing diagnostic tests shall obtain evidence from the manufacturer that the equipment meets the accuracy specifications. The evidence shall include equipment model, serial number, the name and signature of the person of the test laboratory verifying the accuracy, and the instrument accuracy. All diagnostic testing equipment is subject to re-calibration when the period of the manufacturer’s guaranteed accuracy expires.

The apparatus for fan pressurization duct leakage measurements shall consist of a duct pressurization and flow measurement device meeting the specifications in NA2.1.2.

The nominal air handler airflow used to determine the target leakage rate for compliance for an air conditioner or heat pump shall be 400 cfm per rated ton of cooling capacity. Nominal air handler airflow for heating-only system furnaces shall be based on 21.7 cfm per kBtu/hr of rated heating output capacity.

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 13-2 shows the leakage criteria and test procedures that may be used to demonstrate compliance.

Table 13-2 – Duct Leakage Tests

Case	User and Application	Leakage Compliance Criteria (% of Nominal Air Handler Airflow)	Procedure(s)
Sealed and tested new duct systems	Installer Testing HERS Rater Testing	6%	NA2.1.4.2.1
Sealed and tested altered existing duct systems	Installer Testing HERS Rater Testing	15%	NA2.1.4.2.1
Sealed and tested altered existing duct systems	Installer Testing and Inspection HERS Rater Testing and Verification	Fails Leakage Test but All Accessible Ducts are Sealed Inspection and Smoke Test with 100% Verification	NA2.1.4.2.2 NA2.1.4.2.3 NA2.1.4.2.4

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 +25 Pa with respect to outside with all ceiling diffusers/grilles and HVAC equipment installed. When existing ducts are to be altered, this test shall be performed prior to and after duct sealing. The following procedure shall be used for the fan pressurization tests:

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

• For newly installed or altered ducts, verify that cloth backed rubber adhesive duct tape has not been used.

• Seal all the supply and return registers, except for one return register or the system fan access. Verify that all outdoor air dampers and /or economizers are sealed prior to pressurizing the system.

• Attach the fan flowmeter device to the duct system at the unsealed register or access door.

• Adjust the fan flowmeter to produce a + 25 Pa (0.1 in 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.

• Record the flow through the flowmeter (Q_total,25) - this is the total duct leakage flow at 25 Pa.

• Divide the leakage flow by the total fan flow determined by the procedure in Section NA2.1.4.1 and convert to a percentage. If the leakage flow percentage is less than the criteria from Table 13-2 the system passes.

• Duct systems that have passed this total leakage test will be sampled by a HERS rater to show compliance.

For altered existing duct systems that do not pass the leakage test NA2.1.4.2.1, the objective of this test is to show that all accessible leaks are sealed. The following procedure shall be used:

• At a minimum, complete the procedure in NA2.1.4.2.1 to measure the leakage before commencing duct sealing.

• After sealing is complete use the same procedure to measure the leakage after duct sealing.

All duct systems that could not pass either the total leakage test or the leakage reduction test must be verified by a HERS rater to demonstrate compliance. This is a sampling rate of 100 percent.

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:

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 duct surroundings, with all grilles and registers in the duct system sealed.

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

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.

For altered existing duct systems that fail to be sealed to 15 percent of total fan flow, the objective of this inspection is to confirm that all accessible leaks have been sealed. The following procedure shall be used:

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

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

Visually inspect to verify that portions of the duct system that are excessively damaged have been replaced. Ducts that are considered to be excessively damaged are:

• Flex ducts with the vapor barrier split or cracked with a total linear split or crack length greater than 12 inches.

• Metal ducts with rust or corrosion resulting in leaks greater than 2 inches in any dimension.

• Ducts that have been subject to animal infestation resulting in leaks greater than 2 inches in any dimension.