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Eight months of the year, a furnace here is running. October through May, it's the thing standing between the house and the cold outside. That's most of the calendar, not just the deep winter stretch most people picture. A furnace built for a milder climate gets a break most of the year. One here doesn't get that break. The burners, the blower, the ignition system all see more hours of work, year after year, than the same unit would see almost anywhere else in the country.
NOAA nClimDiv, 1991–2020 normals
Half the homes in Knox County were built in 1957 or earlier.
A furnace going into one of those houses needs sizing that matches the house, not the box the old unit came in.
Gas heats 67.4% of homes in Knox County. That's two out of three houses, and it's why gas furnaces are the thing contractors here install, service, and carry parts for. A handful of homes run on electric heat, and a smaller share run on propane, but gas is what the supply chain here is built around. Replacing a gas furnace with another gas furnace means the gas line, the vent, and the fuel setup are already in place. That keeps the job simpler and keeps the house running on the fuel it was already built to use.
A new furnace gets sized to the house, not to the box the old one came in. That sizing takes a look at the house you actually have. Getting it right from the start is the sensible plan.
Find a contractorEight months of work a year adds up fast. Pick a furnace for what it has to do here, not for the lowest price on the quote. A unit sized and built for this kind of run time holds up better than one that's just cheap to install.
A higher efficiency rating costs more up front but burns less gas to make the same heat. Ask what the rating is and ask how it's achieved, because a condensing furnace vents differently than an older style and needs a drain line for condensate. Know that before you compare prices, not after.
A furnace sized by square footage alone is a guess. A proper load calculation looks at insulation, windows, ductwork and layout to find the right output for the house. If a contractor quotes a size without asking about any of that, the number came from somewhere other than your house.
Estimates for a typical Knox County home, from EIA household energy data, Illinois fuel prices and NOAA climate normals. Your home will differ.
Installation day starts before anyone touches the old furnace. A contractor shuts off the gas, pulls the old unit, and checks the ductwork and vent while the space is open, because that's the only time to catch a return that's too small or a flue that needs work too. Setting the new furnace means leveling it, connecting the gas line, wiring the control board, and tying into the existing ducts or modifying them if the new unit's dimensions don't match the old one. The vent pipe gets connected next, and on a condensing furnace that means running a drain line for condensate, something an older furnace never needed. Once it's hooked up, the contractor fires it up, checks the gas pressure, confirms the temperature rise is in range, and watches the burners cycle before calling it done. A furnace that starts clean and holds a steady flame on that first run is a good sign the install was done right.
