Q. What are the most important elements of an
 efficient HVAC and duct system?

A. There are four elements: 

  • The duct system must have a good design that is planned early in the construction process and understood by the builder, framer, structural engineer and truss company. Every fit and bend in the duct system affects the efficiency of the system.
  • The system must be properly installed with the correct amount of airflow and refrigerant verified through the tests listed in the appendix of the ACM.
  • The system must be appropriately sized according to Air Conditioning Contractors of America standards.
  • There must be easy access to the coil for maintenance.

Q. What are "sealed ducts"?

A. Ducts are tubes that make up a system to distribute heated or cooled air to various rooms throughout a house. Sealed ducts have appropriately installed joints and connections to minimize leakage of conditioned air. Air leakage cannot be seen by the naked eye, therefore, diagnostic testing verifies leakage and, by using complying tapes, mastics and mechanical fasteners or aerosol sealant, leaks can be closed.

Q. What is a "Duct Blaster®"?

A. A Duct Blaster® is a tool used to test the air leakage rate of forced air duct systems. The equipment and appurtenances consist of a calibrated fan, pressure tape to temporarily seal all the registers and grilles, flexible duct to fasten the system to the central return or the air handler cabinet of the duct system; and a digital monometer to measure fan flow and duct pressure.

Duct leakage is measured by either pressurizing or depressurizing the duct system and precisely measuring the fan flow and duct pressure. Duct leakage measurements are used to diagnose and demonstrate leakage problems, estimate efficiency losses from duct leakage, and certify the quality of duct system installation.

Q. Do all houses have to have their duct systems sealed?

A. Not necessarily. It depends on the compliance approach. Under the Title 24 Prescriptive Compliance Method ducts must be sealed in all climate zones. Under the Performance Compliance Method, the builder may make credit by "trading-off" between the envelope, water heating and space conditioning, but will probably find that duct sealing is the most cost-effective measure.

Q. Can I still put an HVAC forced air unit on a platform in the garage?

A. Yes. The return plenum that is normally located under the platform must contain either a duct to the HVAC unit or be constructed of sealed sheet metal or ductboard, not the commonly used sheetrock or drywall.

Q. What kind of duct tape can I use?

A. You must use a UL 181 approved tape or sealant. Duct tape, which is a cloth-backed tape with rubber adhesive is not permitted in the new Title 24 unless it is used with mastic and a draw band.

Q. What are the new AB970 mandatory requirements for duct systems?

A. The requirements under AB970 include:

  • UL 181 approved tapes and sealants.
  • No cloth-backed rubber adhesive tapes without mastic and a draw band.
  • Building cavities cannot convey conditioned air.
  • Plenum insulation must have a R4.2 resistance factor.
  • Ducts must be supported every four inches to reduce sagging.

In addition, when using the Prescriptive Compliance Approach, every custom home and every seventh production home must be tested by a HERS rater. In many cooling load zones, a thermostatic expansion valve (TXV) is required to meter the correct amount of refrigerant in a system.

Q. What is a "HERS" rater?

A. A HERS rater is an energy expert certified by the California Energy Commission (CEC) to rate homes in California according to the Home Energy Rating System (HERS). These services include field verification and diagnostic testing to differentiate energy efficiency levels among homes tested for duct efficiency and envelope leakage for compliance with current building efficiency standards. You can locate a HERS rater at

Q. What do I have to do to be a HERS rater?

A. To become a HERS rater, you must take a certification exam and become certified by CHEERS. To do this you can take a training program through CHEERS that provides technical instruction on the rating procedures and background on residential construction and home heating and cooling equipment.

Q. What is CHEERS?

A. The California Home Energy Efficiency Rating System or CHEERS, is a non-profit educational organization that trains and provides services to HERS raters. CHEERS has been approved by the California Energy Commission as a "Provider" for HERS.

CHEERS also provides information to consumers and builders on energy efficiency and provides a listing service to find a HERS rater who can measure the energy efficiency of a home. You can learn more about CHEERS by visiting or calling, 1-800-4-CHEERS.

Q. Do I need to seal the ducts in multi-family housing?

A. Yes, if the Prescriptive Compliance Method is used, the ducts must be sealed according to the minimum requirements described above. Open-ended fan coils may not be used in a sheet rock plenum unless the plenum is lined with sealed ductboard or sheet metal. See Chapter 4 of the California Energy Commission's Residential Manual for details on duct testing and sealing.

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