© Copyright CalCERTS, Inc. 2019
Code Cycle: 2016 and 2019 Standards
Reference: 2019 CalCERTS Alterations Training Manual Chapter 3, Section 2
150.1(c)13 HVAC System Bypass Ducts: Bypass ducts that deliver conditioned supply air directly to the space conditioning system return duct airflow shall not be used.
RA220.127.116.11 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.
Bypass Ducts - Performance Approach in New Construction only!
Bypass ducts are not allowed in newly constructed homes unless they have been specifically modeled in the compliance calculations using the performance approach. Therefore, HERS Raters are required to verify newly installed zoned duct systems to ensure that they are consistent with what was modeled and what appears on the CF1R:
- A visual inspection shall confirm that bypass ducts that deliver conditioned supply air directly to the space conditioning system return duct airflow are not used; or
- If the Certificate of Compliance indicates an allowance for use of a bypass duct, the bypass duct shall conform to the specifications given on the Certificate of Compliance.
Alternative to Bypass Ducts - Dump Zones
Wherever possible bypass ducts should be avoided due to the impact on efficiency. An alternative approach is to send the “excess air” back into conditioned space rather than directly back into the return air. These are not considered bypass ducts if the air has a chance to mix with house air in a way that does not substantially change the return air temperatures. The area in the home where the excess air is sent to is referred to as a “dump zone”. These dump zones will generally be over conditioned by this excess air and are usually unoccupied portions of the home, such as hallways, stairwells or vaulted ceiling areas above the occupied zones.