Quick answer
Air conditioning is the process of cooling indoor air by pulling heat and moisture out of it and moving that heat outdoors, most often with a refrigerant loop driven by a compressor.
An air conditioner does not make cold. It carries heat out of the house, the same way a refrigerator carries heat out of its box, and dries the air as it goes.
Quick facts
The key facts about Air Conditioning, with sources:
- What it does
- Removes heat (sensible load) and moisture (latent load) from indoor air
- US households using AC
- 88% in 2020 1
- Most common type
- Central AC or central heat pump: 82.69 million homes 2
- Federal minimum, split central AC
- 13.4 SEER2 North; 14.3 SEER2 Southeast and Southwest (under 45,000 BTU/h) 3
- Refrigerant limit for new systems
- GWP below 700 (EPA), 1 January 2025 5
- Who can handle refrigerant
- EPA Section 608 certified technicians 6
Key takeaways
- An AC moves heat from inside to outside. It also dries the air, which is half of why it feels comfortable.
- Nearly 9 in 10 US households use some form of air conditioning 1.
- Central systems dominate; window and wall units still cool about 21 million homes 2.
- Efficiency is rated in SEER2; the federal floor depends on where the unit is installed 3.
- New systems must use lower-GWP refrigerants such as R-454B or R-32 5.
- Refrigerant leaks and charging are pro work; owners can keep filters clean and coils clear.
What air conditioning actually does
Most people think of an AC as a machine that blows cold air. A better picture is a heat pump running one way.
It soaks up heat from the air in your house and dumps that heat outside.
The air that comes back out of the vents is cooler because it has lost heat, not because cold was added.
The second job is drying. Warm air holds more water vapor than cool air. When room air passes over the cold indoor coil, some of that vapor condenses into water and runs down a drain. HVAC pros call this the latent load. The temperature part is the sensible load.
That is why a house at 75°F with 40% humidity feels better than one at 72°F with 65% humidity. A well-sized AC handles both.
How an air conditioner works, step by step
Every common AC, from a window unit to a central system, runs the same refrigeration cycle.
- A fan pulls warm room air across the cold indoor coil, called the evaporator.
- Liquid refrigerant in the coil boils into a gas as it absorbs the heat. Moisture condenses on the coil and drains away.
- The compressor squeezes that gas, which raises its pressure and temperature.
- The hot gas flows to the outdoor coil, where a fan blows outdoor air across it and the refrigerant gives up its heat and turns back into a liquid.
- An expansion valve drops the pressure, which chills the liquid, and the loop starts again.
The refrigerant never gets used up. If a system needs more, it has a leak.
Types of air conditioning in US homes
| Type | Homes using it as main AC (2020) | What it is |
|---|---|---|
| Central AC or central heat pump | 82.69 million | Outdoor unit plus indoor coil, air sent through ducts. See central air conditioning. |
| Window or wall unit | 21.43 million | Everything in one box through a window or wall sleeve. |
| Portable AC | 2.68 million | Rolls on the floor, vents hot air through a hose. |
| Ductless mini-split | 1.76 million | Outdoor unit feeding wall or ceiling heads. See ductless mini-split. |
| Evaporative (swamp) cooler | 0.95 million | Cools by evaporating water; works in dry climates only. Not a refrigerant AC. |
Worked example: what a SEER2 change means in kilowatt-hours
SEER2 is BTU of cooling per watt-hour of electricity over a season. Take a home that needs 24 million BTU of cooling in a year (an assumed load, for illustration). Compare the national split-AC minimum with the ENERGY STAR heat pump level 3 4.
| Unit | Math | Electricity used |
|---|---|---|
| 13.4 SEER2 (federal minimum, North) | 24,000,000 BTU ÷ 13.4 BTU/Wh | About 1,791 kWh |
| 14.3 SEER2 (minimum, South) | 24,000,000 ÷ 14.3 | About 1,678 kWh |
| 15.2 SEER2 (ENERGY STAR level) | 24,000,000 ÷ 15.2 | About 1,579 kWh |
| Saving, 13.4 → 15.2 | 1,791 − 1,579 | About 212 kWh, or 12% |
Multiply the kWh saved by your own electric rate to get dollars. The saving grows with cooling hours, so it matters more in Phoenix than in Seattle. The SEER2 savings calculator runs this with your numbers.
Where AC ratings and terms show up
- On the yellow EnergyGuide label on the outdoor unit, which shows SEER2.
- On the AHRI certificate, which rates the outdoor unit with a specific indoor coil and furnace or air handler.
- On the data plate on the unit side, which lists model, serial (often the build date), refrigerant type and charge.
- On a quote, as tons (12,000 BTU/h each), SEER2 and EER2.
- On your electric bill, as summer use above your spring and fall baseline.
Benefits and drawbacks
Benefits
- Keeps indoor heat at a safe level during heat waves, which matters for older adults and people with health conditions.
- Lowers indoor humidity, which limits mold growth and dust mites.
- Filters the air it moves when a good filter is in place.
- A heat pump version also heats the home in winter.
Drawbacks
- Electric use rises sharply in summer, and can strain the grid at peak times.
- Oversized units cool fast but leave air damp and clammy.
- Refrigerants are potent greenhouse gases if they leak 5.
- Does not bring in fresh air; it recirculates indoor air.
Limits of an air conditioner
An AC can only remove heat as fast as its capacity allows. On the hottest days, a correctly sized unit may run for hours and let the house drift a few degrees above the setting. That is normal. Manual J sizing assumes a design day, not the worst day on record 7.
Ratings are measured in a lab at set conditions. Leaky ducts in a hot attic, a dirty filter or the wrong refrigerant charge can cut real output a lot. The rating also does not cover the duct system at all.
Evaporative coolers are not air conditioners in this sense. They add moisture, so they only work well where the air is very dry.
What drives AC cost, lifespan and warranty
Cost depends on type and scope. A window unit is a retail purchase. A central system adds an outdoor unit, an indoor coil, a line set, electrical work, a permit and sometimes duct repair. Higher SEER2 tiers, variable-speed compressors and hard-to-reach attics raise the price.
Age matters too. EIA counted 10.55 million homes whose main AC was 20 or more years old in 2020 2. Older units often use R-22, which can no longer be made in or imported into the US, so repairs get harder.
HyreHVAC prints dollar ranges only where enough dated quotes back them. Use the HVAC replacement calculator for an estimate, and check the parts and labor warranty terms on every quote.
How a central AC installation goes
- Load calculation (Manual J) to size the unit to your home 7.
- Match the outdoor unit to an indoor coil and blower; check the AHRI pairing.
- Pull the mechanical and electrical permits your city requires.
- Recover old refrigerant (EPA 608 certified tech), remove old equipment 6.
- Set the pad, run or reuse the line set, wire the disconnect, connect the drain.
- Evacuate the lines, release or add charge, start up and record readings.
- Final inspection by the local building department.
Keeping an AC running well
- Check the filter every month in summer; change it when you cannot see light through it.
- Keep the outdoor unit clear of plants, leaves and grass clippings, about 2 feet all around.
- Gently rinse the outdoor coil with a garden hose from inside out, with the power off at the disconnect. Never use a pressure washer.
- Look at the drain pan and float switch near the indoor unit for standing water.
- Book a yearly professional check before the cooling season. See HVAC maintenance for what a visit should include.
Warning signs that need a technician
- Ice on the indoor coil or the copper suction line: turn cooling off, run the fan only, and call. This often means low airflow or a leak.
- Warm air from vents while the outdoor fan runs.
- Hissing or bubbling at the coil or lines; refrigerant leaks need a certified tech 6.
- Water leaking from the air handler or a tripped float switch.
- Breaker trips, burning smell or loud buzzing outdoors: turn the system off at the thermostat.
- Check urgency with the is-this-an-emergency tool.
Rules for air conditioners
DOE efficiency (10 CFR 430.32). Central air conditioners made on or after 1 January 2023 must meet 13.4 SEER2 nationally.
Split units under 45,000 BTU/h installed in the Southeast or Southwest must meet 14.3 SEER2; 45,000 BTU/h and up need 13.8.
The Southwest adds EER2: 11.7 for units under 15.2 SEER2, or 9.8 at 15.2 and up 3.
EPA refrigerants (40 CFR Part 84). New residential and light commercial AC systems must use a refrigerant under 700 GWP, compliance date 1 January 2025. EPA lists no installation deadline for systems whose parts were all made or imported before that date. Existing R-410A systems can keep running and be repaired 5.
EPA Section 608. Technicians who service or dispose of equipment that could release refrigerant must be certified 6. Read more in our EPA 608 research.
Air conditioning compared with related equipment
| Equipment | Cools | Heats | Key difference |
|---|---|---|---|
| Air conditioner | Yes | No | Moves heat one way only |
| Heat pump | Yes | Yes | Reversing valve runs the cycle both ways |
| Evaporative cooler | Yes, in dry air | No | Adds moisture; no refrigerant |
| Dehumidifier | No | Slightly warms | Removes moisture only |
| HVAC system | Yes | Yes | The whole set, including ventilation |
Common misconceptions
- Myth Setting the thermostat lower cools the house faster.
- Reality An AC delivers the same cooling rate at 60°F or 74°F. A lower setting only makes it run longer.
- Myth An AC needs a refrigerant top-up every year.
- Reality Refrigerant is not consumed. Needing more means a leak that should be found and fixed.
- Myth R-410A air conditioners are now banned.
- Reality Existing systems can run and be serviced. The EPA rule restricts new systems 5.
- Myth Bigger is better.
- Reality An oversized unit short-cycles and leaves humidity high. Size from a load calculation 7.
Why your region changes the AC you can buy
DOE splits the country into three cooling regions. In the Southeast, which includes Texas, Florida, Georgia and North Carolina, and in the Southwest, which includes Arizona and California, new split air conditioners under 45,000 BTU/h need 14.3 SEER2.
The Southwest also has an EER2 floor because peak afternoon heat matters there. Everywhere else the floor is 13.4 SEER2 3. Cooling degree days tell you how hard your AC works each year.
When this matters to you
If you are choosing a new system, decide first whether you want cooling only or cooling plus heat. A heat pump costs little more than an AC in many cases and replaces some or all furnace use.
If you are repairing an older unit, check its refrigerant and age. An R-22 unit with a leak is usually a replace decision. Run the numbers in the repair-or-replace calculator, then compare picks on our best air conditioners page.
Questions about Air Conditioning
How does an air conditioner work?
An air conditioner moves heat from inside to outside using refrigerant. The refrigerant absorbs heat at the indoor coil, a compressor raises its pressure and temperature, and the outdoor coil releases the heat. An expansion valve then chills the refrigerant so it can absorb more heat.
Does an air conditioner remove humidity?
Yes. Water vapor condenses on the cold indoor coil and drains away, so the air leaves drier. A unit that is too large for the home runs short cycles and removes less moisture, which is why some homes feel cold but clammy.
What is the difference between an air conditioner and a heat pump?
A heat pump is an air conditioner that can run in reverse. A reversing valve lets it pull heat from outdoor air in winter and move it inside. An AC only cools, so it is paired with a furnace or another heat source.
What SEER2 rating should an AC have?
At least the federal minimum for where you live: 13.4 SEER2 in northern states and 14.3 SEER2 in the Southeast and Southwest for most home units. Higher ratings pay back faster in hot places with long cooling seasons.
What refrigerant do new air conditioners use?
New systems use refrigerants with a global warming potential under 700, mainly R-454B and R-32, under EPA's rule with a 1 January 2025 date. Older systems use R-410A or, before 2010, R-22. Existing R-410A systems can still be serviced.
Why does my AC freeze up?
The most common causes are low airflow (a dirty filter, closed vents or a failing blower) and low refrigerant from a leak. Turn cooling off, run the fan to thaw it, replace the filter, and call a technician if it freezes again.
How many homes in the US have air conditioning?
EIA found that 88% of US households used air conditioning in 2020. About two-thirds used central AC or a central heat pump as the main unit, and about 21 million homes relied mainly on window or wall units.
Should I turn my AC off when I leave?
Raising the setting while you are out usually saves energy, because the house gains heat more slowly when it is warmer inside. A programmable or smart thermostat can bring it back down before you return. Avoid letting a humid home get very hot for days.
Can I add refrigerant to my AC myself?
No. Federal rules require EPA Section 608 certification to service equipment that could release refrigerant. Adding charge without fixing the leak also wastes money. A certified technician should find the leak, repair it and charge by weight or by readings.
How long does an air conditioner last?
It depends on climate, use and care, so treat any single figure with caution. EIA counted 10.55 million homes whose main AC was 20 or more years old in 2020. Our lifespan research explains what the data shows.
Sources
- U.S. EIA, Today in Energy: Nearly 90% of U.S. households used air conditioning in 2020 (31 May 2022), retrieved .
- U.S. EIA, 2020 RECS Table HC7.1, Air conditioning in U.S. homes, by housing unit type (final data March 2023), retrieved .
- eCFR, 10 CFR 430.32, Energy and water conservation standards (version of 1 September 2026), retrieved .
- ENERGY STAR, Air Source Heat Pumps Key Product Criteria, retrieved .
- U.S. EPA, Technology Transitions HFC Restrictions by Sector, retrieved .
- U.S. EPA, Section 608 Technician Certification, retrieved .
- ACCA, Manual J Residential Load Calculation (8th Edition), retrieved .
Expert review
Written by the HyreHVAC Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Counts from EIA RECS 2020 HC7.1; minimums read from the eCFR text of 10 CFR 430.32; refrigerant status from EPA's sector table on 10 October 2026. The SEER2 example divides an assumed seasonal load by the rated SEER2 values and nothing else.
Suggest a correction. We fix errors and say what changed.