Nine in ten Maryland households run some kind of air-conditioning equipment, and most of that is central. But the number worth remembering is 80%, the share of homes on a central system, because it sets the maintenance conversation that follows for the rest of this page.
What homes in Maryland actually cool with
Start with the raw split. According to the U.S. Energy Information Administration’s Residential Energy Consumption Survey, 91% of Maryland homes use air-conditioning equipment of some kind. Of those, 80% run a central air-conditioning unit, the kind tied to ductwork and a single outdoor compressor. Another 20% rely on individual equipment: a ductless mini-split, a window or wall unit, or a portable machine rolled from room to room. Ceiling fans show up in 66% of homes, doing the cheap work of moving air so the compressor doesn’t have to run as hard.
That 20% individual figure is where the real story sits in a lot of states, and it’s worth explaining why. In Connecticut, air conditioning shows up in 90% of homes but central systems cover only 34%, meaning most Connecticut households are cooling room by room. Alabama sits at the other end, 94% with AC and 81% central, almost identical shares. Maryland’s numbers, 91% and 80%, land closer to the Alabama pattern than the Connecticut one: when a Maryland home has cooling, it’s very likely ducted and centralized rather than pieced together with window units.
That doesn’t mean individual equipment is rare here. One in five homes still leans on it, whether that’s a converted attic room with no ductwork, an older rowhouse in Baltimore never built for central air, or a sunporch addition cooled by a window unit rather than an expensive duct extension. The survey doesn’t break out why a given household chose one over the other, only what’s installed. And what’s installed tracks construction history: homes built before central air became standard in the mid-20th century often never got retrofitted, so they still lean on individual units decades later. A published share describes what exists, not what a builder would recommend starting from scratch today.
How much cooling the year actually asks for
Baltimore’s reference station reaches or passes 90 degrees Fahrenheit on 24.6 days a year on average, based on NOAA’s 1991-2020 climate normals. That’s a count of days at one weather station, not a statewide average and not a measure of how hot the typical afternoon feels. It’s the number that tells you how often cooling equipment gets pushed to its limit rather than just idling along at a mild setting.
Here’s the part that makes a state-by-state page like this useful instead of decorative: the equipment mix and the heat load don’t automatically line up. A hot state can still be dominated by window units if its housing stock is older or its climate only recently turned muggier than builders planned for. A mild state can be almost entirely central if its homes were built during a boom era when ducted systems were the default, regardless of how many 90-degree days actually show up. The RECS data and the NOAA data are measuring two completely different things, one what’s installed, the other what the weather asks of it, and nothing forces them to agree.
In Maryland’s case they do largely agree. Nearly 25 days a year above 90 degrees is a real, sustained cooling season, not an occasional heat wave, and it matches a housing stock where 80% of homes already run central systems built to handle that load continuously. This isn’t a state where residents are patching together window units against summers that outgrew their equipment. The heat load and the equipment mix point the same direction, which is one reason central-system maintenance, not room-unit shopping, is the more relevant conversation for most Maryland households.
Wet heat or dry heat, and what it changes
Maryland summers bring about 12.6 inches of rain across June, July and August, out of 45.0 inches for the full year, per NOAA’s monthly climate normals at the same Baltimore-area reference station. June averages 3.98 inches, July 4.48, August 4.09, a fairly even spread rather than one soggy month propping up the seasonal total. That figure is precipitation, not humidity. It says nothing about dew point or how sticky the air feels on a given afternoon, and it shouldn’t be read as either.
What it does tell you matters for how an air conditioner should be run. A compressor does two jobs at once: it lowers the air temperature, and it condenses moisture out of the air as that air passes over the cold coil. Removing moisture takes time, specifically run time at a steady pace, not a short blast. In a dry-summer climate, the unit’s job is almost entirely about temperature, and a quick cycle down to the set point does the job fine. In a wetter one like Maryland’s, a meaningful share of the compressor’s work is wringing water out of the air, and that only happens if the system runs long enough to do it.
This is exactly why an oversized unit causes trouble in a place like Maryland specifically. It races down to the thermostat’s set temperature, shuts off, and never runs long enough to pull the humidity down with it. The room reads “cool” on the thermostat while still feeling damp and clammy, because the two jobs, cooling and drying, were never actually finished together. Three practical adjustments follow from that:
- Favor longer, steadier run cycles over short blasts, even if that means a slightly higher thermostat setting during peak afternoon heat.
- Use the “auto” fan setting rather than “on,” since a fan running continuously between cooling cycles can blow the just-collected moisture back into the room.
- Resist sizing a unit for the hottest possible day. A system sized to run longer, more consistent cycles handles Maryland’s wetter summer air better than one built purely to chase peak temperature.
Sizing a room unit, from the published chart
For the 20% of Maryland homes running window, wall, portable, or mini-split units rather than central systems, ENERGY STAR publishes a straightforward area-to-capacity chart for room air conditioners. It’s reproduced below exactly as published, with no rows added and nothing interpolated between the listed steps.
| 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 |
Treat this as a starting point, not a final answer. It applies to a single room and a standalone or ductless unit, and it’s the kind of chart worth checking before buying any of that individual equipment covering one-fifth of Maryland households. It does not size a central air-conditioning system. A central unit serving an entire house is sized through a load calculation that accounts for insulation, window area, orientation and duct layout, something a contractor works out room by room and zone by zone, not read off a single table.
The chart’s biggest practical warning applies just as much in Maryland as anywhere: buying bigger than the room calls for is a real fault, not a safety margin. An oversized room unit cools the air fast, shuts off, and never runs long enough to pull moisture out along with the heat, leaving exactly the cold-but-clammy result described above, just concentrated in one room instead of spread across a whole house.
What actually needs looking after here
Since 80% of Maryland homes run central systems, the ductwork caveat below applies to most households here, though not the one in five running window or portable units with no ducts to worry about.
ENERGY STAR’s filter advice is unambiguous: “Inspect, clean, or change air filters once a month in your central air conditioner, furnace, and/or heat pump.” Once a month, not once a season, and the instruction covers all three pieces of equipment together, which matters for anyone assuming filter care is only a furnace chore. Skipping it has a measurable cost. ENERGY STAR also states that “airflow problems can reduce your system’s efficiency by up to 15 percent,” which means a system in otherwise perfect working order can still be quietly burning extra energy over a Maryland summer simply because nobody swapped a filter.
For the central systems that make up most of Maryland’s cooling equipment, ductwork itself is worth a look too. ENERGY STAR notes that “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.” That’s air conditioned at real cost, leaking into an attic or crawlspace before it ever reaches a vent, which explains a lot of rooms that never quite cool down even when the compressor sounds like it’s working hard. This point doesn’t apply to the fifth of Maryland homes running window units with no ducts involved at all.
A seasonal pass worth running before Maryland’s cooling season peaks:
- Check or replace filters on the schedule ENERGY STAR recommends, monthly, for any central system, heat pump, or furnace filter shared between seasons.
- Have visible ductwork inspected for leaks or disconnected sections if the home runs central air, since sealing losses recovers cooling that’s currently being paid for and never delivered.
- For homes on individual units, confirm the unit was sized against the ENERGY STAR chart above rather than bought purely on convenience.
For the furnace or heat pump side of the same ductwork, the Maryland heating and cooling hub covers what pairs with a central AC system here. Readers comparing how a different climate handles the same equipment mix can see the wetter, cooler contrast in the Vermont air conditioning page, or a middle-of-the-country comparison in the Missouri air conditioning page.