Indiana’s heating season opens in October, when the statewide reference station’s average temperature first drops below the 65°F mark used to calculate heating degree days. The season runs about eight months, peaks in January, and doesn’t fully let go until June. That’s the short version. Here’s what actually shapes your heating bill and your first cold night.
When the heating season starts in Indiana
The 65°F threshold isn’t arbitrary. It’s the base the National Oceanic and Atmospheric Administration uses to calculate heating degree days, a standard way of measuring how much (and for how long) a building needs heat. At Indianapolis, the reference station for this state’s climate normals, October is the first month where the 30-year average temperature (55.5°F) falls below that line. That’s your starting point, not a date you circle on the calendar. A monthly normal is an average built from three decades of data. It tells you the shape of the season, not the morning your furnace kicks on. Some years the first real cold snap lands in late September; other years October stays mild and the first frost waits until Halloween. The number describes a pattern, not a promise.
Demand peaks in January, with 1,131 heating degree days that month, the highest of the year at this station. The season then tapers through spring, with the average climbing back above 65°F in June. Here’s the month-by-month breakdown, straight from NOAA’s 1991-2020 Climate Normals for Indianapolis:
| Month | Heating Degree Days |
|---|---|
| January | 1,131 |
| February | 910 |
| March | 702 |
| April | 355 |
| May | 131 |
| June | 14 |
| July | 1 |
| August | 2 |
| September | 58 |
| October | 314 |
| November | 650 |
| December | 983 |
This table is worth sitting with for a minute. It shows a season with a long, slow ramp-up in fall, a hard core through the winter months, and an equally slow retreat into spring. That shape matters more than any single “start date” ever could, because it tells you when your system is working lightly and when it’s working hard. Keep in mind this data comes from one station, Indianapolis. A county in the northern part of the state, or one tucked against Lake Michigan’s lake-effect belt, can see colder normals and an earlier practical start to heating season than what’s reflected here.
How hard the winter works here
Indianapolis logs about 5,250 heating degree days a year on the 65°F base, against roughly 1,139 cooling degree days. Heating degree days are essentially a proxy for fuel use: if one winter tallies twice the degree days of another, expect roughly twice the fuel burned to keep the same house at the same temperature. That relationship is what makes the annual figure useful for comparing places, not just describing them.
The monthly table above is what keeps that annual number honest. Two places can post the same yearly total for very different reasons: one might have a long, mild season that never gets brutally cold but drags on for months, while another crams nearly the same total into a short, harsh stretch. Indiana’s pattern, based on the table, leans toward the former. The season stretches across eight months, but the coldest three (December, January, February) do the heavy lifting, together carrying a big share of the annual load. That’s useful to know if you’re deciding how much insulation upgrade work matters versus how much a well-timed furnace tune-up matters. A long, moderate season rewards steady, ongoing efficiency. A short, brutal one rewards a system that can handle peak demand without straining.
What most homes in Indiana actually heat with
According to the U.S. Energy Information Administration’s Residential Energy Consumption Survey, Indiana households lean heavily on one type of system and one fuel:
| Equipment / Fuel | Share of Homes |
|---|---|
| Furnace (main heating equipment) | 82% |
| Central heat pump | 7% |
| Steam or hot-water boiler | 3% |
| Natural gas (main fuel) | 65% |
| Electricity (main fuel) | 26% |
| Propane (main fuel) | 7% |
Fuel oil and kerosene weren’t reported with a usable estimate for the state, which means the survey didn’t gather enough data to publish a reliable figure, not that nobody uses it.
A furnace dominating the landscape here tells you what got installed when Indiana’s housing stock was built and what fuel was cheap and available at the time. It’s not a verdict on what’s best for your house today. Furnaces paired with natural gas do one thing very well: they push a lot of heat, fast, through a home’s ductwork, which matters on the coldest January mornings when the temperature difference between inside and outside is at its widest. What they don’t do well on their own is efficiency at partial load, since a furnace tends to run in short, forceful bursts rather than a steady trickle. The maintenance item furnace owners skip most often, and pay for later, is the air filter. A clogged filter forces the blower to work harder, cuts airflow to rooms, and in worse cases can cause the system to overheat and shut itself down on the coldest night of the year, which is exactly when you don’t want that call to your local heating and cooling company page a guide covering wood heat that’s part of this same series.
Run it once before you need it
A heating system tends to fail on its first real workout of the season, on a cold night when every technician in the area already has a full schedule. The fix is to find that failure early, in October, while there’s still time to get someone out. Here’s the order that matters, cheapest and quickest first:
- Turn the thermostat down, then back up above room temperature, and listen for the system to kick on within a minute or two. No response, or a strange delay, is your first clue something needs attention.
- Let it run a full cycle. A burnt-dust smell in the first few minutes is normal, that’s just dust that settled on the heat exchanger over the summer burning off. It should fade quickly. If it lingers or smells like something else entirely, shut the system off and call a technician.
- Check the air filter and replace it if it’s dirty. This is the single most common source of weak airflow and short-cycling, and it’s the cheapest fix on this list.
- Walk the house and clear space around vents, registers, radiators, or the outdoor unit of a heat pump. Furniture, curtains, and stored boxes block airflow and make the system work harder for less heat in the room.
- Test the carbon monoxide alarm. A furnace burning natural gas or propane produces carbon monoxide as a byproduct, and a cracked heat exchanger or blocked vent can send it into the house instead of outside. A working alarm is the cheap insurance against a real hazard.
- If the system doesn’t respond, smells wrong beyond the initial dust burn-off, trips a breaker, or the carbon monoxide alarm ever sounds, stop and call a licensed technician rather than troubleshooting further yourself.
Even a system that passes every one of these checks isn’t the whole story. According to the U.S. Department of Energy, “in a typical house, about 20%-30% of the air that moves through the duct system is lost due to leaks, holes, and poorly connected ducts.” That’s air, and the heat it carries, escaping into an attic or crawlspace before it ever reaches the room you’re trying to warm. A furnace in perfect working order can still leave a bedroom cold if the ductwork feeding it is full of gaps.
What turning it down is actually worth
The Department of Energy puts a number on the most common piece of thermostat advice out there: “You can save as much as 10% a year on heating and cooling by simply turning your thermostat back 7-10°F for 8 hours a day from its normal setting.” That’s a yearly figure, tied to a specific setback range held for a specific stretch of hours, covering both heating and cooling together, not a per-degree formula and not a heating-only number.
In a state where the heating season stretches across roughly eight months, that setback has a lot of hours to work with. A programmable or smart thermostat set back overnight or during the workday, consistently, through October’s mild stretch and January’s peak alike, accumulates savings across a season this long in a way it simply couldn’t in a place where the furnace only runs for six or eight weeks a year. The setback doesn’t need to be dramatic to add up. It needs to be consistent, for as many of those eight months as the house can tolerate it.