Variable-Speed Heat Pump and a Smart Thermostat: Title 24 Rules
A variable-speed heat pump may be paired with a third-party smart thermostat if the two together can modulate compressor speed to follow the load. The installer tests that configuration and certifies it on the CF2R. With backup heat, the thermostat must also show outdoor temperature, lock out backup above 35 F and flag backup use.
- Choose your report
- Upload your plans
- Pay securely
- Permit-ready report by email
What counts as third party
The manual describes third-party thermostats as ones made to work with any system rather than proprietary to the HVAC manufacturer. Some pairings need a special adapter from the HVAC manufacturer, which the installer must configure.
The 2025 modulation rule
Section 150.0(h)9A requires the space-conditioning system and thermostat together to be capable of responding to heating and cooling loads by modulating compressor speed, and to meet the thermostat requirements of Section 150.0(i)2. Under 150.0(h)9B, the installer certifies on the Certificate of Installation that the control configuration was tested using the CF2R procedure. The tested item is that specific pairing.
If there is backup heat
- Outdoor temperature arrives from a sensor or an internet weather service and is displayed.
- Supplementary heat locks out above 35 F, apart from defrost or emergency heat.
- An indicator shows when supplementary or emergency heat is in use.
An exception applies where another control device already performs the lockout (Section 150.0(i)2). The gas furnace case is in heat pump with gas furnace backup.
Baseline thermostat rules
Every heating or cooling system without a central energy management control system needs a setback thermostat whose clock allows at least four programmed periods in 24 hours (Sections 150.0(i)1 and 110.2(c)1). When refrigerant-containing parts are replaced, all thermostats associated with the system become setback thermostats (150.2(b)1Fi). If the weigh-in charge route is used below 55 F outdoors, the thermostat must also meet the demand responsive specifications of Section 110.12 (Exception 1 to 150.2(b)1Fiib).
Questions for the installer before final
- Which thermostat and adapter were configured, and was the CF2R modulation test run with that exact pair?
- If backup heat is installed, is outdoor temperature visible on the screen?
For whether Title 24 requires a smart thermostat at all, see the smart thermostat FAQ. Job lists are in the heat pump checklist, and the zone question is on swapping AC for a heat pump. Reports start at residential Title 24.
Common Title 24 Questions
- When is Title 24 required for a home?
- Does a remodel need Title 24?
- Does a room addition need Title 24?
- What plans are needed for a residential Title 24 report?
- How much does a residential Title 24 report cost?
- How long does a residential Title 24 report take?
Frequently Asked Questions
Yes, provided the system and thermostat together can modulate compressor speed and the installer certifies the tested configuration on the CF2R (Section 150.0(h)9).
If the heat pump has supplementary heat, yes. Section 150.0(i)2 requires the display unless another control device performs the 35 F lockout.
Explore Heat Pumps
- Does California Require a Heat Pump When You Replace an AC?
- What SEER2 Does California Require for a Home AC or Heat Pump?
- Can I Swap My Central AC for a Heat Pump? What Title 24 Adds
- Heat Pump Replacement Title 24 Checklist
- Heat Pump With a Gas Furnace Backup: What Title 24 Requires
View all Heat Pumps guides → · HVAC and Water Heating · Title 24 guide