When to Switch From AC to Heat in Indiana

Last October my friend Lisa in Carmel called me after dark. She'd run the AC all afternoon because it hit 76 outside. By 9pm it was 47 and her living room felt like a walk-in cooler. She grabbed space heaters and shut the AC off entirely. Then the house got damp and stale. She asked me, 'When am I supposed to turn on heat in Indiana, anyway?' That's the real question, right? Indiana fall is a wild ride. One day you're sweating in Broad Ripple, the next you're scraping frost off your windshield in Fishers.

The short answer: don't wait for a date on the calendar. Turn on heat when your indoor temp drops below what feels comfortable for you. Most folks in Indianapolis, Carmel, and Zionsville like it around 68 to 70 degrees during the day. If your living room is 66 and you're wearing a hoodie indoors, that's your sign. Also watch the humidity. When indoor air falls below 35% relative humidity, you'll feel dry skin, static shocks, and maybe a scratchy throat. That's another sign it's time to switch from AC to heat. In Central Indiana, this usually happens in October — sometimes right after the first cold snap. But don't wait for a freeze warning. By then your house is already cold and you're playing catch-up. So when to turn on heat in Indiana really comes down to comfort, not a date on the fridge.

Set Your Thermostat Like You Live There

Forget the 'set it and forget it' nonsense for fall. The weather swings too much. Start with 68 degrees when you're home and awake. Drop it a few degrees when you're gone or asleep. I know some folks in Westfield who keep it at 72 all winter and then complain about gas bills. Don't do that. A smart thermostat can handle the daily ups and downs. But even a basic one works if you adjust it a couple times a day. Big jumps make your furnace short cycle, which wastes energy and wears out parts. So change the temp by two or three degrees at a time, not ten. And if you've got a heat pump, you'll want to set it to Heat and let it run longer at lower output. That's actually more efficient.

One more thing about fall thermostat settings: if you feel a chill from the vents, that doesn't mean the system is broken. Heat pumps blow air that's warm, not hot like a gas furnace. It's maybe 85 to 95 degrees coming out of the register. Your body temp is 98.6, so it can feel cool even though it's heating the room. Give it a few minutes.

Heat Pumps and Indiana Falls: Yes, They Work

I hear this a lot from homeowners in Greenwood and Brownsburg: 'Heat pumps don't work in Indiana winters.' That's an old myth. Modern cold-climate heat pumps can heat your home down to well below freezing. Most have a balance point around 30 to 35 degrees. That's the outdoor temp where the heat pump can't keep up by itself and needs backup heat. But in fall — September, October, even parts of November — a heat pump is the most efficient way to heat your home. In fact, many days you'll heat for less than you'd pay with a gas furnace.

If you want the best of both worlds, a dual-fuel system pairs a heat pump with a gas furnace. The system automatically picks the cheaper heat source based on the outside temp. So in mild fall weather, the heat pump runs. When it gets into the 20s and teens, the furnace kicks in. This is a smart setup for Indianapolis because our winters swing all over the place. And no, you should not flip on Emergency Heat just because it's cold. Emergency Heat (or Aux Heat) is for when the heat pump breaks down or goes into defrost. It's like a spare tire — you don't drive on it every day.

Before You Flip That Switch

Okay, so you've decided it's time. Do a quick check first.

Change or clean your air filter. A dirty filter chokes airflow and makes your system work harder. It also blows dust and allergens into your house. If you have allergies (ragweed is brutal in early fall around Avon and Plainfield), a clean filter is a cheap fix.

Open all your supply and return vents. Check that furniture isn't blocking a return grille. I've seen couches pushed right up against a return in a Noblesville living room, and the whole upstairs stayed cold because of it. If you've got a furnace, run a 10 to 15 minute test. A little dusty smell is normal at first — that's just the burners heating up after months off. But if the smell persists, or you hear a loud motor noise, shut it down. That could be an inducer motor going bad or a flame sensor acting up. Those are fixable, but you don't want to ignore them. A service call now beats a no-heat emergency in January.

While you're at it, clear leaves and debris from around the outdoor unit. Give it 18 to 24 inches of breathing room. And test your CO and smoke detectors. A furnace that hasn't run in months can have small issues. Better to know now.

If you're in an older home in Indianapolis, check your attic insulation and ventilation. A poorly insulated attic sucks heat right out of your living space and makes your furnace work harder. Adding insulation or fixing ventilation is a bigger job, but it pays off every winter. Also, seal drafts around windows and doors. That's the cheapest energy upgrade you can do.

When to Call a Pro (and What to Ask)

You don't need a permit just to turn on your heat. But if you're replacing an old furnace or thinking about a heat pump conversion, you will need a permit in Indianapolis and most surrounding towns. The HVAC contractor usually pulls the permit and schedules the inspection. That's part of the process, so plan for a day or two of disruption.

If you're not sure whether your system is ready, schedule a heating tune-up. A good tech will check airflow, sensors, controls, and the heat exchanger. You can find typical costs on our furnace tune-up page. It's cheaper than an emergency repair later.

Now, here's my honest opinion as someone who's been around this business for years: if your AC is 15 years old and your furnace is 15 years old, don't just patch them. Look at a heat pump conversion or a dual-fuel setup. Yes, the upfront cost is higher. But the efficiency gains in our shoulder seasons (fall and spring) are real. You'll also get better humidity control in summer if you pair it with a variable-speed air handler. And you won't have to worry about gas prices swinging every winter.

The best next step is to have someone come out and do a load calculation. That tells you what size system your house actually needs, not what the last guy guessed. We'll also check your ducts, electrical panel, and where the outdoor unit would go. Then you get a real quote and a timeline.

If you're ready to stop guessing about when to turn on heat and start heating your home smarter, request a quote. We'll walk you through the options — no pressure, no jargon.