California’s building code sets two different minimum indoor heating standards: rental dwelling units must have heating capable of maintaining at least 70°F in habitable rooms, and newly constructed homes must be built with heating capable of holding at least 68°F where the winter design temperature drops below 60°F. Those baseline numbers sit inside a larger framework of equipment efficiency rules, venting and combustion safety requirements, permit and licensing obligations, and, starting with permits filed on or after January 1, 2026, a significant push toward electrification. Getting any piece of it wrong can mean a property declared substandard, a permit denied, or fines that accrue daily.
Minimum Indoor Temperature Standards
The two temperature rules live in different parts of state law and apply to different situations. Mixing them up is one of the most common mistakes property owners make.
Rental Units: 70°F
Title 25 of the California Code of Regulations, Section 34, requires every dwelling unit or guest room offered for rent to have heating facilities that can maintain a minimum room temperature of 70°F, measured three feet above the floor in all habitable rooms.1Legal Information Institute. California Code of Regulations Title 25, Section 34 – Heating When the tenant doesn’t control the thermostat, the landlord must deliver that heat around the clock. The rule also bans unvented fuel-burning heaters outright and requires all heating devices to be an approved type.
The 70°F standard covers habitable rooms — bedrooms, living areas — not bathrooms or hallways. Older buildings that are exempt from certain construction requirements still must provide temperatures as close to 70°F as their existing equipment can deliver.1Legal Information Institute. California Code of Regulations Title 25, Section 34 – Heating
New Construction: 68°F
The California Residential Code, Section R303.10, sets a different standard for newly built homes. Where the winter design temperature is below 60°F, every dwelling unit must have heating facilities capable of maintaining at least 68°F measured three feet above the floor and two feet from exterior walls in habitable rooms. Portable space heaters can’t be used to satisfy the requirement. The lower threshold reflects that new construction generally has better insulation and tighter envelopes than older rental stock.
When Heat Failure Becomes “Substandard”
Health and Safety Code Section 17920.3 lists “lack of adequate heating” as a condition that, when it endangers occupant safety or welfare, makes a property a substandard building by law.2California Legislative Information. California Health and Safety Code 17920.3 That classification hands local housing inspectors enforcement authority and opens the door to tenant remedies under Civil Code Section 1941.1, which lists heating as one of the basic conditions a rental must meet to be habitable.3California Legislative Information. California Civil Code 1941.1
Equipment and Safety Standards
Meeting the temperature threshold isn’t enough on its own. The equipment itself has to comply with overlapping efficiency, venting, and safety rules drawn from Title 24 and state health and safety law.
Efficiency Minimums
The California Energy Code (Title 24, Part 6) incorporates equipment efficiency floors from the state’s Appliance Efficiency Regulations. Gas-fired central furnaces with single-phase supply and rated input below 225,000 Btu/h must reach a minimum Annual Fuel Utilization Efficiency (AFUE) of 80% for non-weatherized units and 81% for weatherized units.4California Energy Commission. 2025 Single-Family Residential Compliance Manual Heat pumps have their own metric: single-phase split systems, including ductless models, must reach a minimum Heating Seasonal Performance Factor 2 (HSPF2) of 7.5; single-package units need at least 6.7.5Energy Code Ace. Central Air Conditioners, Heat Pumps, and Furnaces – Equipment Minimum Efficiencies
Venting, Combustion, and Unvented Heaters
Gas-fired appliances must be vented with piping that is sealed at every joint, adequately supported, and extended through the roof. Appliances can’t be vented into a fireplace or a chimney that serves one.6Legal Information Institute. California Code of Regulations Title 25, Section 832 – Appliance Vent Installation The rules exist to prevent backdrafting, where exhaust gases including carbon monoxide flow into living spaces instead of outside.
California is stricter than many states on unvented heaters. Health and Safety Code Section 19881 prohibits the sale of any unvented heater designed for indoor dwelling use, with narrow exceptions for electric heaters and certain natural-gas decorative logs meeting standards from the Department of Housing and Community Development. Title 25, Section 34 reinforces this by banning unvented fuel-burning heaters in rental units.1Legal Information Institute. California Code of Regulations Title 25, Section 34 – Heating
Carbon Monoxide Detection
Any dwelling with a fossil-fuel-burning heater or appliance, a fireplace, or an attached garage must have an approved carbon monoxide detector. Health and Safety Code Section 17926 required existing single-family homes to comply by July 1, 2011, other existing dwellings by January 1, 2013, and hotel and motel units by January 1, 2017.7California Legislative Information. California Health and Safety Code 17926 A gas furnace, a wood-burning fireplace, or even just an attached garage triggers the requirement.
Hydronic and Electrical Systems
Boiler and hot-water systems fall under the California Mechanical Code, Chapter 12, which covers hydronic piping, boiler capacity, and safety.8International Association of Plumbing and Mechanical Officials. 2022 California Mechanical Code – Chapter 12 Hydronics Residential hydronic equipment must meet the same general venting and combustion air requirements as forced-air furnaces. Electric heating equipment must comply with the California Electrical Code, which governs wiring, circuit protection, and load calculations, including circuits installed for future electric replacement of gas appliances.9California Energy Commission. 2022 Single Family Residential Compliance Manual – Electric Ready Requirements In rental units, portable space heaters can’t serve as the primary heat source; any electric system relied on must be a permanent, approved installation.
Permits, Licensing, and Inspections
Installing or replacing a heating system in California almost always requires a building permit. New installations, system replacements, and major changes to ductwork or ventilation all trigger the process. The application goes to your local building department and typically includes equipment specifications, load calculations showing the system is properly sized, and documentation of Energy Code compliance.
Who Can Do the Work
Anyone performing heating system work must hold a valid Contractors State License Board (CSLB) license. For warm-air heating systems, the required classification is C-20, covering fabrication, installation, maintenance, and repair of warm-air heating, ventilating, and air-conditioning systems including ducts, flues, thermostatic controls, and air filters.10Contractors State License Board. C-20 – Warm-Air Heating, Ventilating and Air-Conditioning Contractor Licensing is required for any project that needs a building permit or costs $1,000 or more in combined labor and materials.11CA.gov. Before Applying For Exam – CSLB
Third-Party Verification
Beyond the building department inspection, many heating installations require verification by a certified rater. Under the 2025 Energy Code, an Energy Code Compliance (ECC) rater performs field verification and diagnostic testing on items listed in the project’s certificate of compliance. Common mandatory tests include duct sealing verification, cooling system airflow, fan efficacy, and refrigerant charge.12California Energy Commission. Energy Code Compliance Program If a test fails, the contractor fixes the issue and the rater retests before the permit closes. An exception exists for urgent alterations such as emergency furnace replacements, where certificates can be registered after the work but before final permit closeout.
Final Inspection
A local building inspector verifies compliance with the California Mechanical Code and Energy Code after installation. Deficiencies have to be corrected before final approval. Skipping the permit and inspection route creates serious downstream problems: enforcement action, complications at sale, and insurance disputes if an unpermitted system later causes damage.
2025 Energy Code Changes for Permits Filed in 2026
Buildings with permit applications filed on or after January 1, 2026, must comply with the 2025 Energy Code, which pushes noticeably toward electrification.13California Energy Commission. 2025 Building Energy Efficiency Standards The most visible changes affect heating system choices and electrical infrastructure.
The updated code expands heat pump requirements for newly constructed single-family, multifamily, and some nonresidential buildings. New single-family homes must now have a main electrical service panel with at least a 200-amp busbar rating so the home can support electric heating equipment.14California Air Resources Board. Zero-Emission Space and Water Heaters – Frequently Asked Questions Homes built with gas furnaces must still include “electric-ready” wiring and panel capacity so a future owner can switch to a heat pump without a major electrical upgrade.
No statewide ban on gas furnaces in new construction exists yet. The California Air Resources Board has been evaluating a regulation on emissions from new space and water heaters with a potential timeline around 2030, but it hasn’t been finalized.14California Air Resources Board. Zero-Emission Space and Water Heaters – Frequently Asked Questions Some regional air districts are moving faster: the Bay Area Air Quality Management District requires zero-NOx standards for small water heaters manufactured on or after January 1, 2027, and for space heaters manufactured on or after January 1, 2029.
Exceptions for Certain Buildings
Not every structure faces the same standards. Historically significant buildings can qualify for alternative compliance under the California Historical Building Code (CHBC), which lets owners combine the CHBC with the regular building code to provide a reasonable level of safety without destroying character-defining features. Existing mechanical systems that pose safety hazards can remain in place if completely and permanently rendered inoperative, and new heating appliances installed in historic structures must still meet current efficiency standards.15California Department of Parks and Recreation. State Historical Building Code Overview
Warehouses, storage facilities, agricultural structures, and other non-residential buildings with minimal or transient occupancy follow different Energy Code compliance paths based on use classification. Seasonal-use buildings such as recreational cabins may have reduced requirements. The local building department makes the final call on whether a specific building qualifies.
Penalties for Noncompliance
Consequences hit landlords, contractors, and builders differently, and none of them are trivial.
Landlords
A rental without working heat can be declared substandard under Health and Safety Code Section 17920.3, triggering inspection orders and mandatory repairs.2California Legislative Information. California Health and Safety Code 17920.3 Under Civil Code Section 1942.4, if a housing inspector has notified the landlord in writing and the violation remains uncorrected 35 days later through no fault of the tenant, the landlord can’t collect rent or issue a pay-or-quit notice, and faces liability for actual damages plus special damages ranging from $100 to $5,000 along with the tenant’s attorney fees. Local code enforcement can also impose administrative fines that accumulate daily until the problem is fixed.
Contractors
Performing heating work without a required permit violates Business and Professions Code Sections 7110 and 7090. The CSLB can impose civil penalties up to $5,000 per violation, order the contractor to obtain permits and pay any local penalties, and suspend or revoke the license.16Contractors State License Board. Filing a Building Permit Violation Form – CSLB Contractors who fail inspections must correct deficiencies before the system can be approved, and repeated failures can trigger CSLB investigation.
New Construction and Commercial Buildings
For buildings under construction, noncompliance with heating and energy code requirements can result in stop-work orders, denial of occupancy permits, and fines from the local building department. The building simply cannot be legally occupied until the heating system passes inspection. On the workplace side, Title 8, Section 5142 requires employers with mechanically driven HVAC systems to inspect them at least annually, document the inspection, and retain records for at least five years, making them available within 48 hours of a request from Cal/OSHA or an affected employee.17California Department of Industrial Relations. California Code of Regulations Title 8, Section 5142 – Mechanically Driven HVAC Systems A broken or neglected heating system that creates unsafe conditions can draw a citation under general workplace safety duties even though Section 5142 itself targets ventilation.
Tenant Remedies When Heat Fails
If you’re the one living without heat, three routes exist under state law. Under Civil Code Section 1942, if a landlord doesn’t fix the problem within a reasonable time after written or oral notice, you can hire someone to make the repair and deduct the cost from rent, up to one month’s rent, and use the remedy no more than twice in any 12-month period.18California Legislative Information. California Civil Code 1942 After 30 days, the law presumes reasonable time has passed, though a tenant may act sooner when circumstances demand it, such as a furnace failure during a cold snap.
Rent withholding under Section 1942.4 is available once a housing inspector has given the landlord written notice and 35 days have passed without correction. The severest option, constructive eviction under Section 1942, lets a tenant vacate and stop paying rent entirely when a heating failure makes the unit genuinely unlivable and the landlord refuses to act. Courts scrutinize these cases closely. If a judge later decides the conditions didn’t rise to uninhabitable, the tenant remains on the hook for the lease, so documenting everything, giving written notice, and using the repair-and-deduct remedy first is usually the safer path.