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A contractor diagnosing a furnace in St. Louis starts with the burner assembly and heat exchanger, because those are the parts that cycle on and off through the coldest months and accumulate wear faster than anything else in the unit. Homes in St. Louis city, MO run heat about seven months a year, from October through April. The ignition system takes that same load every time the thermostat calls for heat, and cracks in the heat exchanger or a fouled igniter are routine findings after a season like this one has run its course on an aging system. Blower motors and control boards fail too, but the combustion side is what a contractor prices and inspects first.
The Parts of a Furnace a Contractor Checks First
The furnace itself sits in a utility space, basement, or closet and is the piece a contractor goes to first. Inside it, the heat exchanger is the part that fails silently and matters most: cracks there are what make a repair urgent. The burners, igniter, and flame sensor all live inside the cabinet too, and any one of them can be the reason the system stops producing heat.
The blower motor sits at the base of the furnace cabinet and pushes conditioned air into the supply ducts. Near it, the air filter and the flue pipe both draw attention during a repair visit. A blocked filter starves the system of airflow, and a compromised flue affects safe venting of combustion gases.
The drawing shows a typical furnace layout, and a licensed contractor will determine which components are relevant to your specific system and situation.
Find a contractor in St. Louis citySt. Louis City by the Numbers
54 severe weather events were recorded in St. Louis city, Missouri between 2015 and 2024.
NOAA National Centers for Environmental Information, Storm Events Database, bulk CSV export, events 2015-01-01 through 2024-12-31.St. Louis city, Missouri holds 174,111 housing units (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesOwners occupy 45.3% of the occupied homes in St. Louis city, Missouri (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesCodes & Standards Covering Furnace Repair in St. Louis city, Missouri4 rules & standards
What furnace repair looks like in St. Louis
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.
Severe Weather Events in St. Louis city
St. Louis weather puts real strain on furnace components over time. How hard that equipment works is a local fact, and that is part of what shapes the repair picture here.
54 severe weather events, 2015–2024. Source: NOAA National Centers for Environmental Information, Storm Events Database.