Specifications

2008 Residential Appendices RA3-3
Appendix RA3 – Residential Field Verification and Diagnostic Test Protocols
RA3.1.3 Apparatus
RA3.1.3.1 Duct Pressurization
The app
aratus 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 Duct Leakage to Outside (Existing Duct Systems)
The app
aratus 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 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 Smoke-Test of Accessible-Duct Se
aling (Existing Duct Systems)
The apparatus for determining leakage in and verifying sealing of all accessible ducts shall also include means
for introducing controllable amounts of non-toxic visual smoke into the duct pressurization apparatus for
identifying leaks in accessible portions of the duct system. Adequate smoke shall be used to assure that any
accessible leaks will emit visibly identifiable smoke.
RA3.1.4 Procedures
This
section describes the procedures used to verify diagnostic inputs for the calculation of improved duct
efficiency.
RA3.1.4.1 Diagnostic Supply Duct Location, Surface Area and R-value
The pe
rformance calculations in the Residential ACM Manual, Section 3.12.3, 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 for portions of the system. Compliance credit may be taken for one or more of these duct
system improvements in any combination. The procedure in this section is used to verify that the duct system
is installed according to the design and meets the requirements for compliance credit.
RA3.1.4.1.1 Duct System Design Requirements
The de
sign shall show the location of equipment and all supply and return registers. The size, R-value, and
location of each duct segment shall be shown in the design drawing, which shall be cross referenced to the
supply duct details report in the Certificate of Compliance. For ducts buried in attic insulation, the portion in
contact with the ceiling or deeply buried shall be shown and the design shall include provisions for ducts
crossing each other, interacting with the structure, and changing vertical location to connect with elevated
equipment or registers as required. Credit shall be allowed for buried ducts only in areas where the ceiling is
level and there is at least 6 inches of space between the outer jacket of the installed duct and the roof
sheathing above.
RA3.1.4.1.1.1 Verified Duct Design
The sy
stem meets the Verified Duct Design criteria if it is verified to be consistent with a documented duct
design that meets the requirements of this section. 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 design shall have calculations showing 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
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. The duct design shall be based on an industry
standard design methodology such as ACCA Manual D or equivalent, and shall take into account: the available
external static pressure from the air handler, the pressure drop of external devices, the equivalent length of the
duct runs, as well as the size, type and configuration of the ducts and fittings. The duct design specifications
and layout shall be included with the building plans submitted to the enforcement agency, and a copy of the
duct design layout shall be posted or made available with the building permit(s) issued for the building, and