Updated October 2026. Seven mistakes people make when buying an air conditioner, with ENERGY STAR sizing and replacement figures and the EPA refrigerant rules that took effect in 2025.
The costliest mistakes when you buy an air conditioner are picking the wrong size, shopping on sticker price alone, ignoring the efficiency rating and hiring an installer who skips the load calculation. As of October 2026, ENERGY STAR says a certified, correctly installed central AC can save up to 20% on heating and cooling costs versus an old unit.
Jump to: 📸 Size · 💲 Price vs cost · ⏱️ Efficiency · 🤝 Installer · 🏠 Buying or selling · ❓ FAQ
Before you buy an AC
- 88% of U.S. households used air conditioning in 2020 (EIA).
- A room of 300 to 350 square feet needs about 8,000 BTUs per hour; add 4,000 BTUs if it’s a kitchen (ENERGY STAR).
- If your AC is more than 10 years old, ENERGY STAR suggests having it evaluated for replacement.
- Since January 1, 2025, EPA rules restrict certain high-warming refrigerants in new AC equipment.
An air conditioner is one of the bigger checks you’ll write for a house, and you live with the choice for a decade or more. Nearly half of the energy used in a home goes to heating and cooling, according to ENERGY STAR. So a bad pick shows up every month on the power bill. Here are the mistakes we see most, and how to avoid each one.
| Mistake | What it costs you | The fix |
|---|---|---|
| Wrong size | Short cycling, damp air, higher bills | Manual J load calculation or the ENERGY STAR room chart |
| Cheapest unit wins | Higher bills and repairs over 10+ years | Compare running cost, not just price |
| Skipping the efficiency label | More power used every summer | Check SEER2 and the ENERGY STAR label |
| Ignoring the refrigerant | Older equipment that’s harder to service | Ask which refrigerant the unit uses |
| Features you don’t need | Paying for extras you never use | Pick features that fit your routine |
| Not comparing quotes | Overpaying for the same system | Get at least three written bids |
| Weak installer | A good unit that runs badly | Licensed, insured, does a load calc |
Mistake 1: Are you buying the wrong size?
Bigger isn’t better. ENERGY STAR is blunt about it: an oversized air conditioner costs more to buy, wastes energy and doesn’t cool better. It cools the room fast, shuts off, then starts again. That short cycling leaves the air cool but clammy, because the unit never runs long enough to pull out moisture. Too small is no better; it runs all afternoon and never catches up.
For a window or room unit, ENERGY STAR’s chart is a good start. 150 to 250 square feet needs about 6,000 BTUs per hour. 300 to 350 square feet needs about 8,000. 450 to 550 square feet needs about 12,000. Then adjust. Cut 10% for a heavily shaded room. Add 10% for a very sunny one, 600 BTUs for each person past two, and 4,000 BTUs in a kitchen.
For central air or a heat pump, ask for a Manual J calculation. It’s the standard method contractors use to work out how much heating and cooling your house needs, room by room. If a contractor sizes your system by looking at the old unit’s label, that’s a red flag.
Mistake 2: Are you weighing price over the cost of running it?
The cheapest unit on the floor is rarely the cheapest over ten summers. A system that uses more power, or needs more repairs, costs more each year you own it. Before you buy, compare three numbers: the installed price, the estimated yearly energy cost on the yellow EnergyGuide label, and the warranty on parts and the compressor.
Utility rebates can close part of the gap on efficient models. ENERGY STAR’s rebate finder lists offers by ZIP code. Ask your utility too; programs change often.
Mistake 3: Are you ignoring the efficiency rating?
For central systems, the number to read is SEER2, the current version of the seasonal energy efficiency rating. Higher means less power for the same cooling. Bob Vila has a clear explainer if you’re checking the SEER rating for the first time. Then look for the ENERGY STAR label, which is independently certified.
When is it time to replace instead of repair? ENERGY STAR’s rule of thumb: if your heat pump or AC is more than 10 years old, have it looked at. Same if it needs frequent repairs, your bills keep climbing, or some rooms are always too hot. A certified replacement, installed correctly, can save up to 20% on heating and cooling costs.
Mistake 4: Are you overlooking the refrigerant?
Refrigerant used to be an afterthought. Not anymore. Under the AIM Act, the EPA’s Technology Transitions rules restrict certain hydrofluorocarbons in new equipment beginning January 1, 2025. These HFCs can trap hundreds to thousands of times more heat than carbon dioxide. ENERGY STAR lists R-32, R-454B and R-290 as lower-warming refrigerants used in room air conditioners.
What does that mean for you? Ask the dealer which refrigerant a unit uses. A new system on a current refrigerant is easier to service in the years ahead.
Mistake 5: Are you paying for features you won’t use?
Modern units come with a lot of extras: variable-speed compressors, air quality filters, quiet modes and smart connectivity that lets you control the unit from your phone. Some are worth it. Variable-speed technology, which ENERGY STAR says most certified room units now include, saves energy and runs quieter. Others are nice to have.
A smart thermostat is often the better buy. ENERGY STAR says a certified smart thermostat can save about $100 a year in homes with high heating and cooling bills or that sit empty much of the day. Also pick the right type: window, portable, ductless mini-split or central. Homes without ducts are good candidates for a mini-split.
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On homes listed by other agents, Beycome credits you up to 2% of the price at closing (1% kept, $1,499 minimum; not on FSBO homes or homes listed by Beycome sellers).
Buy a home →Mistake 6: Are you buying without comparing options?
Take the time to compare. Get at least three written quotes for a central system, each with the model number, the SEER2 rating, the refrigerant, the warranty and what’s included (permits, removal of the old unit, new line set or pad). Quotes that look very different often cover different work.
For a room unit, buying online is fine. Stores that carry several brands make it easy to compare price, BTUs and energy use side by side. Read the return policy before you open the box.
Mistake 7: Are you hiring an inexperienced installer?
A great unit installed badly runs like a bad unit. Ductwork leaks, the wrong refrigerant charge and poor airflow all cut efficiency. Hire a licensed, insured contractor who does a load calculation, checks your ducts and explains the warranty in writing. Don’t hire someone just because the bid is lowest.
Then keep it running well. Check the filter every month during heavy use and change it at least every 3 months, as ENERGY STAR advises. Book a yearly tune-up, and get in touch with AC repair professionals as soon as you notice odd noises, water around the indoor unit or warm air from the vents. Our guides to signs your AC needs repair and cleaning your air conditioner go deeper, and so does our list of cooling habits that raise your bills.
Does the AC matter when you buy or sell a home?
Yes, a lot. Buyers and inspectors look at the AC’s age, the data plate and how well it cools. If you’re buying, ask for the install date and service records, and price in a replacement if the unit is near the end of its life. The Beycome buyer program has no upfront fee, and on homes listed by other agents it credits part of the buyer-agent commission back to you at closing. That cash can help with a new system. The credit doesn’t apply where no buyer-agent commission is offered, like most FSBO homes, or on homes listed by Beycome sellers.
If you’re selling, a working, serviced AC removes an easy objection. Should you replace it first? Our guide on installing AC before selling weighs it, and how an efficient AC adds value covers the payoff. When you’re ready, a flat fee MLS listing starts at $99, with $0 due to Beycome at closing.
Air conditioner buying questions
What size air conditioner do I need?
For a room unit, ENERGY STAR suggests about 6,000 BTUs for 150 to 250 square feet and 8,000 for 300 to 350. For central air, ask for a Manual J load calculation.
Is a bigger AC better?
No. An oversized unit costs more, wastes energy and cools in short bursts that leave the air damp.
What SEER rating should I look for?
Read the SEER2 rating: higher is more efficient. An ENERGY STAR label means the unit’s efficiency is independently certified.
How old is too old for an air conditioner?
ENERGY STAR suggests having any AC or heat pump older than 10 years evaluated, especially if repairs and bills keep rising.
Does the refrigerant type matter?
Yes. EPA rules restrict certain high-warming HFC refrigerants in new equipment from January 1, 2025. Ask which refrigerant a unit uses.
How often should I change the AC filter?
Check it every month in summer, change it when it looks dirty, and at least every 3 months.
AC use: EIA, 2020 Residential Energy Consumption Survey. Sizing, replacement, filter and thermostat figures: ENERGY STAR. Refrigerant rules: EPA Technology Transitions Program. Follow your equipment maker’s instructions and local codes.
Beycome prices as of October 2026; “$0 at closing” means no Beycome fee at closing (taxes, title and other closing costs still apply). From November 2, 2026, Basic is $129 in California and Illinois ($99 elsewhere). Buyer credit: Beycome keeps 1% of the price (minimum $1,499), lender approval required, not on FSBO homes or homes listed by Beycome sellers. Beycome Title: Florida and Texas today; Michigan, Ohio, Illinois and Indiana starting November 2, 2026. General information.
Sources
- ENERGY STAR, Room Air Conditioners (sizing chart, refrigerants), read October 28, 2026.
- ENERGY STAR, When is it time to replace?, read October 28, 2026.
- ENERGY STAR, Heat and Cool Efficiently, read October 28, 2026.
- ENERGY STAR, Air Source Heat Pumps (Manual J sizing), read October 28, 2026.
- ENERGY STAR, Ductless Heating and Cooling, read October 28, 2026.
- EPA, Technology Transitions Program, read October 28, 2026.
- EIA, Nearly 90% of U.S. households used air conditioning in 2020, read October 28, 2026.
- Beycome, listing package features, October 2026.
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