Furnace replacement in the Bay Area: what it costs in 2026

Air District Rule 9-4 sets a zero-NOx standard for residential and commercial furnaces manufactured after January 1, 2029. It covers Alameda, Contra Costa, Marin, San Francisco, San Mateo and Santa Clara counties and parts of Solano and Sonoma. The Air District says the only appliances that meet the standard today are electric.

Residential fan-type central furnaces manufactured after January 1, 2024 must meet an ultra-low NOx standard. The Air District says gas furnaces that meet it are on the market.

No one has to remove a working furnace. If a furnace fails and is replaced after the 2029 date, the replacement must be zero-NOx. Propane equipment is not covered.

The 2029 date covers furnaces under 175,000 BTU/hr. Furnaces in mobile homes are exempt. The Air District will finish a cost and technology assessment for furnaces before 2029.

The Board vote of November 4, 2026 concerns water heaters under Rule 9-6, not furnaces.

When a central gas furnace is replaced, the Energy Code requires the installer to seal all existing and new ducts and a third-party ECC-Rater to verify them. The target is leakage of 10 percent of system airflow or less, or 7 percent to the outside. If neither is reached, every accessible leak is sealed and checked with a visual inspection and a smoke test.

The duct test is not required for ducts already sealed, tested and certified by a rater, for systems with less than 40 feet of duct in total, or for ducts that contain asbestos. Ducts or equipment in a garage have a stricter limit of 6 percent.

The ECC-Rater is expected to be hired by the builder or the building owner. The installing contractor may hire the rater for an HVAC changeout only if the homeowner authorizes it.

Under the prescriptive rules, a replacement heating unit must burn natural gas or be a heat pump. Electric resistance as the main heat source is allowed only in listed exceptions.

Minimum efficiency for gas central furnaces under 225,000 Btu/h: 80 percent AFUE, or 81 percent for weatherized units.

In San José, installing or replacing a furnace generally takes 3 permits: mechanical, electrical and building. All 3 come from one application at SJPermits.org. The City lists a gas shut-off valve within 6 feet of the unit, a work space of 30 by 30 inches, seismic anchoring, and a raised base for a furnace in a garage.

The federal tax credit for efficient home improvements, which covered gas furnaces, applies to improvements made through December 31, 2025. Some cost guides still mention it.

Silicon Valley Clean Energy pays $2,000 for a heat pump heating and cooling system that replaces a gas furnace, or $3,000 for income-qualified customers.

San José Clean Energy pays $1,500 for a heat pump HVAC system that replaces a gas furnace, or $2,500 in environmental justice communities. Ducted and ductless systems qualify, no existing air conditioner is required, and the system needs a SEER2 of 16 or more.

The C-20 license covers warm-air heating systems and the ducts, registers, flues, thermostats and air filters that go with them.

Gas heat is the norm. In the San Francisco, Oakland and Fremont metro area, 1,094,566 of 1,770,425 occupied homes heat with utility gas. In the San Jose metro area it is 398,221 of 693,483, according to the 2024 American Community Survey.

Bay Area baseline. The Air District study puts the median cost of a like-for-like gas furnace replacement at $6,347 and the average at $6,846, from 2,945 installs in Bay Area single-family homes. It calls the spread of gas furnace costs narrow, at about $3,000.

Age. Fixr says a furnace installed 15 to 20 years ago is near the end of its life.

Repair or replace. This Old House cites a typical lifespan of 15 to 25 years. It says a repair that costs more than half the price of a new furnace, or one on the heat exchanger or control board, often points to replacement.

Size. A furnace that is too large cycles on and off and loses efficiency. One that is too small runs longer and wears out sooner. Fixr says climate, ceiling height, insulation and windows change the size, not just the square footage.

Ducts and access. This Old House lists old, undersized or poorly sealed ducts, an outdated electrical panel, tight spaces and local permit fees as reasons the price rises.

Air conditioning. Bob Vila says an air conditioner installed together with the furnace will likely need replacing at the same time, and doing both at once usually costs less than two separate jobs.

Running cost. In milder climate zones without cooling, the Air District says a heat pump costs about the same to run as a gas furnace, and that this may change with gas and electricity rates.

Model number, fuel, AFUE rating and BTU output, and the load calculation behind that size.

Duct work: sealing, the leakage test by an ECC-Rater, who hires the rater, and any duct sections replaced, in linear feet.

Mechanical, electrical and building permits: which ones the job needs, who pulls them, and whether the fees are in the price.

Vent, gas shut-off valve, seismic anchoring and the clearances around the unit.

Thermostat, air filter, and whether the air conditioner coil or condenser is touched.

Haul-away of the old furnace and patching of any opened walls.

For a heat pump option: ducted or ductless, the electrical work, the SEER2 rating, and which rebate the price assumes.

Warranty in years for the equipment and for labor, the start date, and how many days the house is without heat.