Buying a used air conditioner might not seem like the smartest move. After all, it’s an appliance that’s essential to the air quality and overall comfort of your home. Why spend time scouring Facebook Marketplace and Craigslist only to risk ending up with a unit that coughs dust, constantly rattles, or simply quits after a few weeks? Plus, even a used window AC could run you upwards of $300. All valid concerns. Still, with a bit of caution and a clear understanding of what to look for, you can score a great deal—and do the planet a favor, too.
Americans throw out around 6 million window ACs each year, according to the EPA. While the Clean Air Act requires that all refrigerants be safely removed before disposal—and the EPA’s Responsible Appliance Disposal (RAD) program helps ensure proper handling—around a half-million tons of old units still end up in landfills. Once there, they can release refrigerants with global-warming potential far greater than CO2.
But if a preowned AC is right for you, you should still do your homework—and temper your expectations. “There’s no guarantee with used AC units,” warns Lane Martin, co-founder of the indoor air quality company Modern PURAIR. “But if it’s been well looked after and fits your needs, it could be a good temporary option. Just don’t expect it to last as long as a new one.”
Here’s how to ensure you’re making a smart, informed purchase.
What you need
First, you want to narrow your search for units that are the right fit for you space. Measure your window’s width, height, and depth, and note how it opens (vertically? outwards?). Then measure the square footage of the room, as cooling capacity depends on it. “Units that are too big will cool quickly but won’t dehumidify well, and those that are under-sized will run constantly and dwindle in effectiveness more quickly,” says Alex Atkinson, an HVAC specialist at the California-based Super Brothers. A general rule of thumb is 20 BTUs per square foot. That means a 12,000 BTU window unit will cool about 500–600 square feet.
Finally, check out what kind of electrical outlet is near the window. Most units use a standard 120-volt outlet but some more-powerful ones may need a 240-volt. It’s important to know which you need before you buy.
Where to look
If you want to find a decent used AC, Atkinson recommends first asking HVAC service contractors or suppliers in your area. They may sell remanufactured units that have been inspected, cleaned, and sometimes come with a 6- to 12-month warranty. “That’s a great way of buying used with confidence,” he says.
You might also find decent bargains from a local appliance refurbisher, but make sure they offer some form of performance testing and have a return policy. If you’re buying from an individual off a site like Craigslist or Facebook Marketplace, you need to do a little homework before taking a used model home.
What to look for
No matter where your secondhand AC comes from, it’s worth doing some extra due diligence to ensure you can get several good years out of it. These are four important things to look out for as you shop:
1. A unit that’s less than 8 years old
Most window and portable AC units have a lifespan of about 10 years. “If the unit is already 8-plus years old, you’re buying a machine near the end of its life,” says JB Clerger, owner of JBC Repairs, an HVAC contractor in Orlando, Florida. You can determine the age of an air conditioner by locating the nameplate, which is usually on the side or back, and checking the manufacturer’s date (aka the MFR date). If there isn’t one, look for the serial number: The first four digits typically indicate the month and year of its production.
2. Signs of wear, smells, and sounds
Appearances can be deceiving, so it’s crucial to give the unit a thorough inspection. Come prepared with a checklist to avoid this or other similar scenarios. Look for physical clues like rust, corroded coils, twisted fins, broken wires, or oil spots, which Atkinson says is a telltale sign of a refrigerant leak. Avoid anything that smells strongly of mildew or mold, which may signify buildup in the coils or drain pan, especially if the unit was improperly stored.
Finally, ask the seller to power on the AC. Listen for any noises—if it rattles, grinds, or squeals, it could indicate a failing compressor or fan motor—and test the cooling power: “It should cool fast,” says Clerger, “with no strange noises, and consistent airflow.” If a seller refuses to let you plug it in, walk away.
3. A solid efficiency score
A unit’s Seasonal Energy Efficiency Ratio (SEER) measures how much energy an AC uses over the course of a cooling season. You can find the rating on the yellow-and-black EnergyGuide label on most models—or you can look up the unit’s brand and serial number online. A SEER rating of 14-16 strikes a good balance of cost and efficiency. SEER 17 or higher is considered high efficiency.
Units made in 2023 or after will likely feature the SEER2 rating. This updated testing better reflects the way people actually use air conditioners, and is considered more rigorous. And don’t be confused: SEER2 numbers are slightly lower than the original SEER numbers, so they won’t match up exactly. But the higher the number, the higher the unit’s efficiency.
4. Safer refrigerants
Older models may use R-22 refrigerant, which was once standard but was banned in 2020 due to its ozone-depleting effects. If you follow the under-8-year-old guideline, this shouldn’t be a concern. R-22 was replaced by R-410A, which is better for the ozone but still has high global-warming potential; it was the standard in units made from 2010 to 2023, but is currently being phased out. If you’re lucky enough to find a newer AC, look for those with R-32 or R-454B refrigerant, which represent a new class of refrigerants with far less potential to warm the world.