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Furnace repair in Sonoma County starts with the parts that cycle hardest: the igniter, the burner, and the heat exchanger. Homes in Sonoma County, CA run heat about seven months a year, from November through May. That run stacks real wear on the ignition system, which fires every time the burner lights, and on the heat exchanger, which flexes with every heating cycle through expansion and contraction. A contractor quoting a repair here checks those components first, because they accumulate the most fatigue and are likeliest to show cracks, corrosion, or failure before anything else does.

Furnace repair in a county where the housing stock skews this old runs into a particular problem: the system a contractor opens is rarely the system the house was designed for, but the ductwork feeding it usually is. Half the homes in Sonoma County, California were built in 1979 or earlier (2020-2024 ACS 5-year). That gap between what was built into the house and what was eventually installed to heat it is where repair calls get complicated. A heat exchanger swap or a blower replacement becomes a longer job when the surrounding duct runs were sized and routed for something else. The contractor has to account for what the existing layout does to airflow before settling on what the repair actually requires.
The Parts of a Furnace a Contractor Checks First

The heat exchanger sits at the core of the furnace cabinet, inside the main unit in the utility room, basement, or closet. It is the surface that carries combustion heat into the airstream, and when it cracks or corrodes, combustion gases can migrate into the living space. The burner assembly sits just below it, and a contractor will look at both early.
The blower motor and its fan wheel sit at the base of the cabinet and push conditioned air out through the supply side. The igniter, flame sensor, and gas valve are smaller components grouped near the burner, and each one has a specific job that can stop the furnace from firing or running a full cycle when it fails.
The drawing shows a typical furnace layout, and a licensed contractor determines which components and conditions apply to your specific system.
Find a contractor in Sonoma CountySonoma County, by the numbers
142 severe weather events were recorded in Sonoma County, California between 2015 and 2024.
NOAA National Centers for Environmental Information, Storm Events Database, bulk CSV export, events 2015-01-01 through 2024-12-31.Half the homes in Sonoma County, California were built in 1979 or earlier (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesSonoma County, California holds 207,699 housing units (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesOwners occupy 62.6% of the occupied homes in Sonoma County, California (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesCodes & Standards Covering Furnace Repair in Sonoma County, California5 sourced rules and standards
What happens when the contractor arrives
Non-weatherized gas furnaces manufactured on or after November 19, 2015 must reach 80.0 percent AFUE.
Non-weatherized oil-fired furnaces manufactured on or after November 19, 2015 must reach 83.0 percent AFUE.
Mobile home gas furnaces manufactured on or after November 19, 2015 must reach 80.0 percent AFUE.
Non-weatherized gas furnaces manufactured on or after December 18, 2028 must reach 95.0 percent AFUE, up from the 80.0 percent minimum that applies to units manufactured before that date.
Licensing and Legal Requirements in Sonoma County, California
California requires a state contractor license: it is a misdemeanour to engage in the business of, or act in the capacity of, a contractor in California without one, unless the work is exempt.
Weather Events in Sonoma County That Stress Heating Systems
Extreme weather puts hours on a furnace fast, running it harder and longer than mild conditions ever would. How much strain a system accumulates depends on what the local climate actually delivers, which is why this data belongs on a page about furnace repair in Sonoma County.
142 severe weather events, 2015–2024. Source: NOAA National Centers for Environmental Information, Storm Events Database.
