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




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.


Verified Duct System Design

Procedure for duct system design layout approval and field verification


Duct Leakage

Verify that duct leakage is less than or equal to the compliance criteria given in Table RA3.1-2.


Return Duct Design

Verify compliance with the return duct and return grill sizing requirements of Table 150.0-C or Table 150.0-D).


Air Filter Device Design

Verify compliance with the requirements in 150(m)12.


Verification of Prescriptive Bypass Duct Requirements

Verification to confirm zonally controlled systems comply with the bypass duct requirements in 150.1(c)13



RA3.1.2 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 Supply 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 supply 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.       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. The duct design layout shall be approved by the enforcement agency.