2025 Single-Family Heating, Ventilation, and Air Conditioning (HVAC)

The Energy Code heating, ventilation, and air conditioning (HVAC) requirements apply to newly constructed buildings, and additions and alterations to existing buildings. This includes mandatory requirements for all single-family residential buildings—such as single-family homes, duplexes, and townhouses. When applicable, projects must meet either the prescriptive or performance compliance options. If the HVAC system design does not meet the minimum prescriptive requirements, the performance compliance option allows for tradeoffs to demonstrate compliance.

The heating, ventilation, and air conditioning (HVAC) requirements consist of both mandatory and prescriptive requirements that apply to newly constructed buildings, and additions and alterations to existing buildings. Newly constructed single-family buildings must comply with the mandatory HVAC requirements outlined in Sections 110.0 through 110.3 - PDF, and 110.5, 150.0(e) - PDF, 150.0(h) - PDF, 150.0(i) - PDF, 150.0(j)1B - PDF, 150.0(j)2 - PDF, 150.0(m) - PDF, 150.0(o) - PDF and 150.0(t) - PDF.

The HVAC prescriptive requirements for newly constructed single-family residences are found in Sections 150.1(c)6 through 7 - PDF, 150.1(c)9 through 10 - PDF, and 150.1(c)12 through 13 - PDF. Newly constructed single-family residences may also comply using the performance compliance option for the climate zone in which the building is located. 

Requirements for additions to existing buildings 

Additions to existing single-family residences that include new equipment installed to serve the addition must meet the applicable sections: 

• Section 150.2(a)1C - PDF, 150.2(a)1E - PDF, if the prescriptive approach is used.
• Section 150.2(a)2C-D - PDF, if the performance approach is used.
• The following exceptions may apply for additions:
  • For space-conditioning systems: When heating or cooling is extended to an addition from an existing system(s), the existing heating and cooling equipment is not required to comply with Part 6. The heating system capacity must be adequate to meet the minimum requirements of CRC 303.10.
  • For space conditioning system ducts: When the duct is extended from an existing duct system to serve the addition, the existing duct system and the extended duct must meet the applicable requirements in Section 150.2(b)1Di - PDF and 150.2(b)1Dii - PDF.
  • For Ventilation: Additions that are 1,000 square feet or less do not need to meet the ventilation cooling requirements in Section 150.1(c)12 - PDF.  

Alteration Requirements 

Alterations to existing single-family residential buildings, or alterations in conjunction with a change in building occupancy to a single-family residential occupancy with altered or replacement systems, must meet the applicable sections:  

• Section 150.2(b)1C-G - PDF, 150.2(b)1L-M – PDF, if the prescriptive approach is used.
• Section 150.2(b)2 - PDF, if the performance approach is used. 

Field verification and diagnostic testing (FV&DT) is mandatory for all newly constructed single-family buildings and is prescriptively required for most HVAC additions and alterations. Some mechanical, envelope, and water heating systems require FV&DT prescriptively when modeled for compliance credit under the performance approach. Any FV&DT that is required for a project will be specified on the Certificate of Compliance (CF1R). The building owner, builder, and some types of installers are responsible for completing FV&DT and related documentation and must coordinate with one or more ECC-Raters to provide third-party compliance ratings. Visit Energy Code Compliance Program for more information.

See the CBECC Frequently Asked Questions (FAQs) for more information on modeling different HVAC systems for single-family residences in the California Building Energy Code Compliance (CBECC) software.

No. But per Energy Code Sections 110.0 - PDF and 110.1 - PDF, plug-in room air conditioner and plug-in room heat pump equipment types must meet all applicable state and federal appliance efficiency requirements. For more information on the CA Title 20 appliance regulations, visit the Appliance Efficiency Regulations webpage.  

Yes. Energy Code Sections 110.0 and 110.1 require plug-in room air conditioner and plug-in room heat pump systems to meet any applicable state and federal efficiency requirements. Also, if this is the main heating source for the dwelling, it must meet the minimum sizing requirements of the California Building Code. For more information on the CA Title 20 appliance regulations, visit the Appliance Efficiency Regulations webpage.

Yes. Exception 1 Section 150.0(a)1 - PDF of the 2025 Energy Code applies to a newly constructed single-family dwelling with a ventilated attic when a ductless mini-split system is used to serve the entire dwelling. The exception to mandatory roof insulation applies when:  

• Air handler and ducts are located in conditioned space below the ceiling separating the occupiable space from the attic; or
• The space-conditioning system air handler is located in unconditioned space and has 12 linear feet or less of supply duct, including the length of the air handler and the plenum, located in unconditioned space, with all other portions of the supply ducts located in conditioned space below the ceiling separating the occupiable space from the attic; or
• Space conditioning system is ductless. 

Since the ductless mini-split system falls under the third condition, it is exempt from having to meet the mandatory roof deck insulation requirement under Section 150.0(a)1 - PDF. 

No. All newly constructed dwelling units must meet the mandatory ventilation requirements in Section 150.0(o) – PDF no matter the size of the new dwelling unit.

Yes. Installation of a space conditioning appliance (other than a plug-in room appliance) requires a building permit. It also requires wall penetrations and sturdy mounting to support the indoor fan-coil unit. New HVAC systems require load calculations. If the new system is replacing an old system (an alteration), then removal of the old system requires refrigerant recovery by a technician that holds an EPA 608 Type II or Universal certificate.  

Even though the DIY system is charged at the factory, to complete the installation it must be altered by connecting the indoor unit(s), outdoor unit, and the charged line set at the home. This disqualifies it from the Exception to Section 150.1(c)7A - PDF.

Yes. For computer modeling, include the square footage of any not habitable or indirectly conditioned spaces with the closest habitable zone. See the CBECC Frequently Asked Questions (FAQs) for more information on modeling different HVAC systems for single-family residences in the California Building Energy Code Compliance (CBECC) software. 

Yes. If an exhaust fan is operated continuously to deliver 50 CFM, then the volume of air required of the central fan integrated (CFI) system is reduced to 100 CFM, or an average of 50 CFM over the hour such that the sum of ventilation air delivered averages 100 CFM. A 1,000 CFM furnace providing 10 percent outside air could be used in this case. Even though such a combined ventilation system is partially balanced, it does not qualify as a balanced system in the calculation of Qfan - PDF. 

No. Section 150.1(c)6 – PDF of the Energy Code requires heat pumps to be used for space conditioning for all climate zones. Alternative fuel space conditioning systems like gas furnaces must be modeled under the performance compliance approach. 

Yes. If a new HVAC system is installed for newly constructed buildings, or for additions or alterations to existing buildings, it must meet all the requirements for space conditioning systems which include the prescriptive refrigerant charge verification in all climate zones for heat pumps and in climate zones 2 and 8 through 15 for air conditioners.

No. If existing equipment is used to serve the addition, the refrigerant charge, airflow, and Watt draw requirements do not need to be met as specified by Exception 3 to Section 150.2(a) - PDF. However, if the existing duct system is extended to serve the addition, the entire duct system, i.e., the existing and extended duct, must meet the duct insulation and duct sealing requirements (Exception 4 to Section 150.2(a) - PDF). New ducts in unconditioned space also shall meet the prescriptive duct insulation requirements per Section 150.2(b)1Di - PDF.  

If a new system, equipment and ducting is installed to serve the addition, it must meet all the requirements for space conditioning in a new home which includes prescriptive refrigerant charge verification in all climate zones for heat pumps and in climate zones 2 and 8 through 15 for air conditioners. Additionally, mandatory fan airflow and Watt draw testing is required in all climate zones.  

Yes. If there is a new HVAC system being installed in the addition, in which the airflow is not field verified to be at least 350 CFM per ton, then it must meet the maximum capacity limits provided in Table 150.2-A - PDF and Table 150.2-B - PDF. The maximum capacity limits in Tables 150.2-A and B depend on the relative sizes of the calculated heating design load (HL) and cooling design load (CL), type of space conditioning system, and the duct sizing per Section 150.2(a)1E.

Yes. When doing load calculations for additions, the envelope leakage specified in the load calculation shall be no greater than the value shown in Table 150.2-C - PDF (“average” for many load calculation software tools).

Additionally, if the leakage is established through field verification and diagnostic testing following Reference Residential Appendix RA3.8 - PDF, the tested envelope leakage value may be used in the load calculations and no disclosure is required. 

Yes. Per Exception 1 to Section 150.0(h)1 - PDF, block loads (the total load for all rooms combined that are served by the central equipment) may be used for the purpose of system sizing for additions.  

No. Per Section 150.2(b)1Miib - PDF, alterations or replacements of a vented range hood alone (using existing ducts) do not require ECC-Rater field verification. However, per Section 150.2(b)1L - PDF a new vented range hood with an entirely new duct system must meet the mandatory requirements in Section 150.0(o) - PDF, which will include ECC-Rater field verification. 

Yes. Replacing the outdoor unit (or indoor unit) of a split system by itself will trigger the duct sealing and field verification requirements. The alteration requirements differ from newly constructed building requirements. (See Section 150.2(b)1Ei through iii – PDF for the requirements and exceptions). 

Yes. Per Exception 4 to Section 150.2(a) - PDF, whenever any length of duct is extended from an existing system to serve an addition, the existing duct system and extended duct must meet Section 150.2(b)1Di - PDF and 150.2(b)1Dii - PDF.  

This means that duct leakage testing per Section 150.2(b)1Dii applies to the whole system. The measured duct leakage must meet one of the following: 

• Must be equal to or less than 10 percent of system air handler airflow as confirmed by ECC-Rater testing utilizing the procedures in RA3.1.4.3.1, or
• Leakage to outside shall be equal to or less than 7 percent of system air handler airflow as confirmed by ECC-Rater testing utilizing the procedures in RA3.1.4.3.4; or
• If it is not possible to meet the duct sealing requirements of either Section 150.2(b)1Diiibl, or 150.2(b)1Diibll, then all accessible leaks shall be sealed and verified through a visual inspection and smoke test by a certified ECC-Rater using methods specified per Reference Residential Appendix RA3.1.4.3.5. 

Yes. When a space conditioning system is altered, duct sealing requirements are triggered. If the ducts are not being replaced, the existing duct system needs to be tested by the installer and an ECC-Rater to have no greater than 10% total leakage or 7% leakage to outside per Section 150.2(b)1E – PDF. If this leakage criteria cannot be met, a smoke test and visual verification may be conducted by an ECC-Rater to verify that all accessible ducts have been sealed. 

See the Blueprint for more information, including articles and frequently asked HVAC questions, about the 2025 Energy Code. Additionally, see Chapters 4 and 9 of the 2025 Single-Family Residential Compliance Manual for more information.