Central air, for the most part. Indiana homes lean heavily on ducted systems, with window units, portables and ductless mini-splits filling in around the edges. What that mix looks like, how much summer heat it has to handle, and what to maintain follow below, using federal survey data and NOAA climate normals.
What homes in Indiana actually cool with
The U.S. Energy Information Administration’s 2020 Residential Energy Consumption Survey (RECS) puts air conditioning in Indiana at 94% of homes using air-conditioning equipment of some kind. A central air-conditioning unit serves 81% of homes. An individual unit (a ductless mini-split, a window or wall unit, or a portable) is used in 20% of homes. Ceiling fans turn up in 78% of homes. All four figures are published for Indiana. None is marked Q, the survey’s flag for a sample too small to publish, which is not the same as zero.
These shares are not meant to add up to 94%. A house can have a central system and a window unit in the converted attic bedroom, so it counts in both columns. Read each line as its own question put to the same households.
The useful comparison is the distance between “has air conditioning” and “has a central unit,” which is the share running on individual equipment. Connecticut reports air conditioning in 90% of homes but a central unit in only 34%. Alabama reports 94% and 81%, and Indiana’s published pair is the same. In both states, a central unit is what most households that cool actually have.
A 20% share still means one house in five here runs at least some individual equipment. That includes older homes without ductwork, additions, finished attics and basements, and rentals where a window unit is the landlord’s answer. Those households are working with a different set of tools than the statewide majority.
The data come from the survey’s state table, “Highlights for air conditioning in U.S. homes by state,” available from the U.S. Energy Information Administration. For the other half of the year, Heating a Home in Indiana covers what runs through the same ducts in winter.
How much cooling the year actually asks for
The heat load here is 14.6 days a year reaching 90°F or more. That figure is a count of days at a single reference station, Indianapolis, taken from NOAA’s 1991-2020 Climate Normals. It is not an average summer temperature, and it is not a measure of the whole state. Evansville or Fort Wayne would not necessarily match.
Fourteen and a half days is roughly two weeks of 90-degree weather spread across a summer. That is a modest total next to the months a cooling system may see use, so the count is a better gauge of peak stress than of run time. The 90-degree days are when a marginal system, a clogged filter or an undersized window unit shows itself.
Equipment mix and heat load do not always match. A hot state can run mostly on individual units because its houses were built before central air was common. A mild one can be almost entirely central because its housing went up after ducted systems became the default. What is installed follows when the houses were built, not the thermometer. Indiana’s modest count of 90-degree days sits alongside a mix of 81% central and 20% individual, and nothing in those numbers is out of step. I would not push the reading further, since the temperature count is one city’s record set against statewide survey shares.
The practical point is that a heat load like this does not demand the heaviest equipment. It demands equipment that works properly on the handful of days that count. A correctly sized system with clean filters and sealed ducts will handle a 14.6-day summer. A badly sized or neglected one will struggle on those few days and look fine the rest of the time, which is how people talk themselves out of fixing it.
Wet heat or dry heat, and what it changes
Summers at the Indianapolis reference station are wet-leaning. NOAA’s 1991-2020 monthly normals show about 12.6 inches of rain across June, July and August, out of 43.6 inches for the full year. June averages 4.95 inches, July 4.42, and August, the driest of the three, 3.2. Those are inches of precipitation, not relative humidity or dew point, so they cannot say how muggy a given afternoon feels. They do say that rain is a regular feature of every summer month. They are also normals for one station, describing what a summer can usually bring, not a forecast.
An air conditioner does two jobs. It lowers the air temperature, and it pulls moisture out of the air as warm, damp air crosses the cold coil. Removing moisture takes run time. In a dry summer the work is nearly all temperature. In a wet one, a large share of the work is drying, and that happens only while the compressor is running.
This is why an oversized unit causes trouble. It drops the temperature quickly, satisfies the thermostat, and shuts off before it has dried much of anything. The room reads 72°F and feels cold and clammy. In a dry summer oversizing is merely wasteful (extra cost, short cycling, more wear). In a wetter summer it is a comfort fault as well.
Given a summer like this one, here is what to prioritize:
- Run time over speed. Longer, steadier cycles dry the air better than short bursts of hard cooling. A system that cycles every few minutes is a sign something is off.
- Fan setting. With “auto,” the fan stops with the compressor. With “on,” it keeps blowing, which can push moisture collected on the coil back into the house. Auto is usually the better default in a wetter summer, but check your equipment’s manual before changing it.
- Sizing before purchase. Smaller, correctly matched equipment that runs longer beats a larger unit that cools quickly and stops.
- Airflow. A dirty filter or blocked coil cuts the air crossing the coil, which hurts both cooling and drying.
Sizing a room unit, from the published chart
ENERGY STAR publishes a cooling capacity chart for room air conditioners. It is a starting point for choosing a window or wall unit, and it does not size anything else. Here it is as published, area to be cooled in square feet against capacity needed in BTU per hour:
| Area to be cooled (square feet) | Capacity needed (BTU per hour) |
|---|---|
| 100 up to 150 | 5,000 |
| 150 up to 250 | 6,000 |
| 250 up to 300 | 7,000 |
| 300 up to 350 | 8,000 |
| 350 up to 400 | 9,000 |
| 400 up to 450 | 10,000 |
| 450 up to 550 | 12,000 |
| 550 up to 700 | 14,000 |
| 700 up to 1,000 | 18,000 |
| 1,000 up to 1,200 | 21,000 |
| 1,200 up to 1,400 | 23,000 |
The chart ends at 1,400 square feet, and so does what it can tell you. Do not extend it beyond that line, and do not divide capacity by area to get a per-square-foot rule, because the steps are uneven. Read the row your room falls in and stop there. The chart is published by ENERGY STAR, and it gives no adjustments for ceiling height, sun exposure or number of occupants, so I will not invent any.
It also does not size a central system. A central system is sized by a load calculation, a room-by-room accounting of the house’s heat gain done by a contractor. A rule of thumb applied to a whole house is a common route to the wrong machine.
The larger mistake is treating the next size up as insurance. An oversized unit is a fault, not a margin. It cools the room fast, shuts off, and never pulls much moisture from the air. In a state with rain in every summer month, that outcome is more likely than somewhere drier. If your room falls near the edge between two rows, think about the room rather than buying up by reflex. For the 20% of Indiana homes on individual units, matching the row to the room is the whole sizing job.
What actually needs looking after here
Maintenance should follow the equipment mix. Central systems come first, since 81% of homes have one, and room units come second. The duct caveat applies to only one of the two groups.
If you have a central system
Start with the filter. ENERGY STAR’s guidance reads: “Inspect, clean, or change air filters once a month in your central air conditioner, furnace, and/or heat pump.” It names three pieces of equipment, so a household with a heat pump should not assume the advice is only for furnaces. The interval is once a month, not every few months.
The payoff is stated in the same checklist: “Airflow problems can reduce your system’s efficiency by up to 15 percent.” A system can be in perfect working order and still underperform because air is not moving through it freely, and a clean filter is the cheapest fix there is.
Ducts come next, and only for ducted homes. ENERGY STAR says: “In a typical house, however, about 20 to 30 percent of the air that moves through the duct system is lost due to leaks, holes, and poorly connected ducts.” A room that never cools down is not always a weak air conditioner. The cool air may be leaking into an attic or crawlspace before it reaches the vent.
If you cool with room units
A house on window units has no ducts, so the duct-leak warning does not apply. Your upkeep is the unit itself: its filter, its coil, and the seal around the window frame, where cooled air leaks out and warm air comes in. Take the unit out or cover it at the end of the season, as the manual directs.
Here is a seasonal pass that works for either kind of home:
- Before the first hot spell, replace or clean the filter, and make sure vents and returns are not blocked by furniture or rugs.
- Check the outdoor unit for leaves, cottonwood fluff and grass clippings, and keep plants trimmed back from it.
- Run the system once in spring before you need it, and watch for weak airflow, odd noises or a coil that ices over.
- Inspect the filter monthly through the cooling season, and swap it when it looks loaded.
- If a room stays warm while others are fine, have the ducts checked for leaks before replacing equipment.
To see how another state’s mix looks, read What Do Homes in Delaware Cool With? or What Do Homes in Rhode Island Cool With?
Common questions
What share of Indiana homes have air conditioning?
According to the EIA’s 2020 RECS, 94% of Indiana homes use air-conditioning equipment. Of those, 81% use a central unit and 20% use an individual unit such as a mini-split, window or wall unit, or portable. The figures overlap because some homes use both.
How hot do Indiana summers get?
At the Indianapolis reference station, NOAA’s 1991-2020 normals show a mean of 14.6 days a year reaching 90°F or more. That is a count of days at one station, not an average temperature and not a statewide figure.
What size window unit does my room need?
ENERGY STAR’s chart is the starting point. A room of 250 up to 300 square feet, for example, falls in the 7,000 BTU per hour row. It applies to room units only and does not size a central system.
How often should I change my air filter?
ENERGY STAR says to inspect, clean, or change air filters once a month in your central air conditioner, furnace, and/or heat pump. During heavy summer use, keep that monthly check, since a filter can look fine in March and be loaded by July.