California’s building code heating requirements set two different minimum temperatures depending on the building: existing rental units must have heating that can hold at least 70°F in habitable rooms, and newly built homes must be designed to maintain at least 68°F where the winter design temperature falls below 60°F. On top of those temperature floors, the state regulates equipment efficiency, venting, carbon monoxide detection, permits, licensed installation, and third-party verification. Miss any of them and the property can be declared substandard, the permit can be denied, or the fines can start running daily.
Minimum Indoor Temperatures
Two separate rules apply, and they are often confused.
For rental dwelling units and guest rooms, Title 25 of the California Code of Regulations, Section 34, requires heating facilities capable of maintaining a minimum room temperature of 70°F, measured three feet above the floor in every habitable room. When the tenant does not control the thermostat, the landlord has to provide that heat around the clock. The standard covers bedrooms and living areas, not bathrooms or hallways. Older buildings that are exempt from certain construction rules still have to deliver temperatures as close to 70°F as the existing equipment allows.1Legal Information Institute. California Code of Regulations Title 25, Section 34 – Heating
For newly built homes, the California Residential Code, Section R303.10, applies. Where the winter design temperature is below 60°F, every dwelling unit must have heating facilities capable of maintaining at least 68°F at a point three feet above the floor and two feet from exterior walls in all habitable rooms. Portable space heaters cannot be used to satisfy that requirement.
The Health and Safety Code backs both standards up. Section 17920.3 lists “lack of adequate heating” as a condition that makes a building substandard when it endangers occupant safety or welfare.2California Legislative Information. California Health and Safety Code 17920.3 That classification gives local housing inspectors enforcement authority and opens the door to tenant remedies.
Equipment and Safety Standards
Any heating system installed in California has to meet overlapping efficiency, venting, and safety rules.
Efficiency Minimums
The California Energy Code (Title 24, Part 6) incorporates equipment efficiency minimums from the state’s Appliance Efficiency Regulations. Gas-fired central furnaces with single-phase electrical supply and rated input below 225,000 Btu/h must meet a minimum Annual Fuel Utilization Efficiency (AFUE) of 80% for non-weatherized units and 81% for weatherized units.3California 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, and single-package units must reach 6.7.4Energy Code Ace. Central Air Conditioners, Heat Pumps, and Furnaces – Equipment Minimum Efficiencies
Venting, Unvented Heaters, and Carbon Monoxide
Gas-fired appliances must be properly vented. Joints must be sealed, piping adequately supported, and the vent extended through the roof. Appliances cannot be vented into a fireplace or a chimney that serves a fireplace.5Legal Information Institute. California Code of Regulations Title 25, Section 832 – Appliance Vent Installation The point is to prevent backdrafting of exhaust gases, including carbon monoxide, into living space.
California goes further on unvented heaters than most states. Health and Safety Code Section 19881 prohibits the sale of any unvented heater designed for use inside a dwelling, with narrow exceptions for electric heaters and certain natural-gas decorative logs that meet standards developed by the Department of Housing and Community Development. Title 25, Section 34 separately bans unvented fuel-burning heaters in rental units.1Legal Information Institute. California Code of Regulations Title 25, Section 34 – Heating
Any dwelling with a fossil-fuel-burning heater or appliance, a fireplace, or an attached garage must have an approved carbon monoxide detection device. Health and Safety Code Section 17926 required single-family homes to comply by July 1, 2011, other existing dwellings by January 1, 2013, and hotel or motel units by January 1, 2017.6California Legislative Information. California Health and Safety Code 17926 A gas furnace, a wood-burning fireplace, or an attached garage is enough on its own to trigger the requirement.
Hydronic and Electric Systems
Boiler-based and hot-water heating falls under the California Mechanical Code, Chapter 12, which covers piping, boiler capacity, and safety.7International Association of Plumbing and Mechanical Officials. 2022 California Mechanical Code – Chapter 12 Hydronics Residential hydronic systems have to meet the same general venting and combustion air rules as forced-air furnaces. Electric heating equipment must comply with the California Electrical Code for wiring, circuit protection, and load calculations.8California Energy Commission. 2022 Single Family Residential Compliance Manual – Electric Ready Requirements In rental units, portable space heaters cannot serve as the primary heat source; electric heat has to be a permanent, approved installation.
Permits, Licensed Contractors, and Inspections
Installing or replacing a heating system almost always requires a building permit from the local building department. New installations, system replacements, and major modifications to ductwork or ventilation all trigger the permit process. The application typically has to include equipment specifications, load calculations sizing the system to the space, and documentation of Energy Code compliance.
Anyone performing the work must hold a Contractors State License Board license. The relevant classification for warm-air heating is C-20, which covers fabrication, installation, maintenance, and repair of warm-air heating, ventilating, and air-conditioning systems including ducts, flues, thermostatic controls, and air filters.9Contractors State License Board. C-20 – Warm-Air Heating, Ventilating and Air-Conditioning Contractor A license is required for any project that needs a building permit or costs $1,000 or more in combined labor and materials.10CA.gov. Before Applying For Exam – CSLB
Many heating installations also require third-party verification. Under the 2025 Energy Code, the Home Energy Rating System (HERS) program has been replaced by the Energy Code Compliance (ECC) program. A certified ECC-Rater performs field verification and diagnostic testing on items listed in the project’s certificate of compliance, which commonly includes duct sealing verification, cooling system airflow, fan efficacy, and refrigerant charge.11California Energy Commission. Energy Code Compliance Program If a test fails, the contractor corrects the issue and the rater retests before the permit can close. Emergency furnace replacements and similar urgent alterations can have certificates registered after the work but before permit finalization. The local building inspector then does the final check against the Mechanical and Energy Codes. Skipping the permit and inspection process creates lasting problems: enforcement action, trouble selling the property, and insurance complications if an unpermitted system causes damage.
2025 Energy Code Changes for 2026 Permits
Buildings whose permit applications are filed on or after January 1, 2026, have to comply with the 2025 Energy Code.12California Energy Commission. 2025 Building Energy Efficiency Standards The code expands heat pump requirements for newly constructed single-family, multifamily, and some nonresidential buildings. New single-family homes must have a main electrical service panel with at least a 200-amp busbar rating, so the home can support electric heating equipment.13California Air Resources Board. Zero-Emission Space and Water Heaters – Frequently Asked Questions Homes built with gas furnaces still have to include electric-ready wiring and panel capacity so the owner can switch to a heat pump later without a major electrical upgrade.
There is no statewide ban on gas furnaces in new construction as of 2026. The California Air Resources Board has been evaluating a regulation targeting emissions from new space and water heaters, with a potential timeline around 2030, but it has not been finalized.13California Air Resources Board. Zero-Emission Space and Water Heaters – Frequently Asked Questions
Penalties for Noncompliance
The consequences fall on different parties depending on who ignored which rule.
Landlords
A rental with no working heat can be declared substandard under Health and Safety Code Section 17920.3, which triggers inspection orders and mandatory repairs.2California Legislative Information. California Health and Safety Code 17920.3 If an inspector gives written notice and 35 days pass without correction, Civil Code Section 1942.4 bars the landlord from collecting rent or serving a pay-or-quit notice, and exposes the landlord to actual damages plus special damages of $100 to $5,000 and 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 the permits and pay any local penalties, and suspend or revoke the license.14Contractors State License Board. Filing a Building Permit Violation Form – CSLB Failed inspections have to be corrected before the system can be approved, and repeated failures can trigger a CSLB investigation.
New Construction and Commercial Buildings
On a construction project, noncompliance with heating and energy code requirements can produce stop-work orders, denial of occupancy permits, and local fines. The building cannot be legally occupied until the heating system passes inspection. For commercial buildings, Title 8, Section 5142 requires employers with mechanically driven HVAC systems to inspect those systems at least annually, document the inspection in writing, and keep the records for at least five years, available to Cal/OSHA or an affected employee within 48 hours of a request.15California Department of Industrial Relations. California Code of Regulations Title 8, Section 5142 – Mechanically Driven HVAC Systems A neglected heating system that creates unsafe working conditions can draw a citation under general workplace safety duties.
Tenant Remedies When Heat Fails
California Civil Code Section 1941.1 lists heating as one of the basic conditions a rental must meet to be habitable, specifically “heating facilities that conformed with applicable law at the time of installation, maintained in good working order.”16California Legislative Information. California Civil Code 1941.1 When the landlord does not fix a heating problem, tenants have three main options.
The first is repair and deduct. Under Civil Code Section 1942, if the landlord does not act within a reasonable time after written or oral notice, the tenant can hire someone to make the repair and deduct the cost from rent. The deduction cannot exceed one month’s rent, and the remedy can be used no more than twice in any 12-month period.17California Legislative Information. California Civil Code 1942 After 30 days the law presumes the landlord has had a reasonable time, though a tenant may act sooner when circumstances demand it, such as a furnace failing during a cold snap.
The second is rent withholding under Civil Code Section 1942.4, available after a housing inspector has given the landlord written notice and 35 days pass without correction through no fault of the tenant.
The third is to vacate. When the failure is severe enough to make the unit genuinely unlivable and the landlord refuses to act, Section 1942 lets the tenant move out and stop paying rent.17California Legislative Information. California Civil Code 1942 Courts look at these cases closely. If a judge later finds the conditions were not actually uninhabitable, the tenant remains bound by the lease. Document everything, give written notice, and work through repair-and-deduct first where possible.
Buildings That Don’t Follow the Standard Rules
Not every structure has to meet the same heating standards. Historically significant buildings can qualify for alternative compliance under the California Historical Building Code, which allows owners to combine it with the regular building code to reach a reasonable level of safety without destroying character-defining features. Existing mechanical systems that pose safety hazards can remain if completely and permanently rendered inoperative, and new heating appliances still have to meet current efficiency standards.18California Department of Parks and Recreation. State Historical Building Code Overview
Non-residential buildings such as warehouses, storage facilities, and agricultural structures face different expectations because they typically have minimal or transient human occupancy. The California Energy Code applies different compliance paths depending on use classification. Seasonal-use buildings, including recreational cabins, may also have reduced requirements. The local building department makes the final call on whether a specific building qualifies for an exemption.
One boundary worth flagging: California’s workplace temperature rules do not mirror the residential heating minimums. Cal/OSHA’s indoor standard at Title 8, Section 3396 targets heat illness and only engages when indoor temperatures reach 82°F; it does not set a minimum warm temperature for workplaces.19Department of Industrial Relations. California Code of Regulations Title 8, Section 3396 – Heat Illness Prevention in Indoor Places of Employment If you are looking for a floor on how cold an office can be, the building code and Section 5142 maintenance duties are where to look, not the heat illness standard.