Takes about a minute. No obligation.
Most homes in Marion County heat with utility gas, just over half. Electricity comes next at 28%, and propane or LP gas heats another 16.6%, common where gas lines don't reach. If your house already has a gas line run to a furnace, replacing it with another gas furnace is usually the straightforward path. It's the setup your contractor sees most often here, and the venting, gas line and ductwork are already built for it. If your home runs on propane or electric heat instead, that's worth saying up front, since the install looks different.
NOAA nClimDiv, 1991–2020 normals
Half the homes in Marion County were built in 1973 or earlier.
A furnace going into a house that old has to match the ducts and venting already there, not the other way around.
At that gas price, a high-efficiency condensing furnace still costs less to run every month than a standard one. It just takes longer to earn back whatever extra it cost to install. If you're planning to stay in the house a long time, that extra efficiency keeps paying you back the whole time you own it. If you're not sure how long you'll be there, a mid-efficiency model that costs less upfront can make more sense. Either way, the bigger question is whether the unit matches your ductwork and venting. A furnace that's sized and installed wrong will cost you more in comfort and repairs than the efficiency rating will ever save you.
Heat here runs October through April. September is the last month to replace a furnace before it has to carry the house through winter. Doing it now means the ductwork and venting get checked on a normal schedule instead of during the first cold week.
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Half these houses were built in 1973 or earlier, which means the ductwork and vent setup already on site came with the house, not with whatever furnace goes in next. Before swapping in a new unit, a contractor needs to check the duct sizing and the venting against what the new furnace actually needs. A furnace that moves more air than the old ducts were built for will run loud and uneven. One that vents differently than the old setup may need new venting run to do it safely.
A furnace should be sized by a load calculation that looks at the house itself, its square footage, windows, insulation and layout. If a contractor quotes a size based only on the old furnace or a quick glance at the house, ask how they arrived at it. The wrong size is the one mistake efficiency ratings and warranties can't fix later.
The furnace is one part of a system that includes the ducts carrying air and the vent carrying exhaust out of the house. A new furnace that moves air differently than the old one needs those ducts checked, and a furnace that vents differently may need new venting run. Get this in writing before the install, not discovered after.
Estimates for a typical Marion County home, from EIA household energy data, Illinois fuel prices and NOAA climate normals. Your home will differ.
Installation day starts with the old furnace coming out, along with the old venting if the new unit doesn't use the same type. The contractor sets the new furnace, connects the gas line, and runs new venting where the old path doesn't match what the new furnace needs. Ductwork gets tied in next, with any transitions or plenum changes needed to match the new unit's airflow. Once it's wired and connected, the contractor fires it up and checks the gas pressure, the temperature rise across the furnace, and the airflow at the vents. A combustion analyzer gets used to check the exhaust itself, not just whether the furnace turns on. The last step is going through the thermostat settings and any filter or maintenance needs before they leave.
