Furnace Installation in O'Fallon, MO
A new furnace here will run from October through April every year. Tell us about the house, and a licensed contractor who covers St. Charles County will get in touch.
Tell us about the job
It takes about a minute.
Seven months of heat, and a furnace that has to keep up
O'Fallon needs a working furnace from October through April. That's seven months of the year, with winter nights averaging 25°F. A new furnace here runs that stretch without much of a break.
Most homes in the area heat with gas, and any non-weatherized gas furnace built after November 2015 has to reach at least 80 percent AFUE by federal rule. That's the floor, not a feature. Storms are part of the picture too. St. Charles County has seen 84 damaging wind events and 9 winter storms over the past ten years, and statewide, 19% of households went at least 24 hours without power in 2024. Worth keeping in mind when you're deciding what kind of furnace, and what backup, makes sense for your house.
- 7 months
- October through April, your furnace is on duty
- 25°F
- the average winter night it heats against
- 66%
- of homes here heat with gas, so most furnaces here burn gas
- 80% AFUE
- the federal minimum any new unit must meet
NOAA nClimDiv, 1991–2020 normals
A high-efficiency gas furnace would save about $160 a year to run in St. Charles County compared with a gas furnace.
Estimates for a typical St. Charles County home, from EIA household energy data, Missouri fuel prices and NOAA climate normals. Your home will differ.
- What size furnace does my house need?
- The right size comes from a load calculation, not a rule of thumb or the size of the unit you have now. A contractor measures your square footage, insulation, window count, and ceiling height, then runs a Manual J calculation to find the actual heat loss of your home. A furnace that's too big cycles on and off too fast and never runs long enough to heat evenly. One that's too small runs constantly and still can't keep up on a 25°F night. There's no shortcut that replaces this measurement, and a contractor will size it for your specific house.
- How do I know it's time to replace my furnace?
- Frequent breakdowns and repair calls are the clearest sign, especially if each visit costs more than the last. Watch for uneven heat between rooms, a furnace that runs longer than it used to, or a rising gas bill with no other explanation. If a repair would cost a large share of what a new furnace costs, replacing it usually makes more sense than patching an old one. Homes here need heat from October through April, so a furnace that's already struggling in fall has a full winter of 25°F nights ahead of it before spring.
- Is a high-efficiency furnace worth it?
- It depends on how much you heat and how long you plan to stay in the house. Every new non-weatherized gas furnace sold today has to hit at least 80 percent AFUE by law, so even a standard model wastes less fuel than older units did. High-efficiency furnaces go beyond that minimum, which matters more here since homes need heat for 7 months of the year. Close to two thirds of households in the area heat with gas, so the fuel savings from a more efficient furnace add up over a full heating season. A contractor can walk through the specific models and what each one would mean for your house.