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What Size Air Conditioner Do I Need?

a homeowner calculating what size air conditioner they need

If you’re in the market for a new air conditioner, you’re probably wondering, “What size air conditioner do I need?” Obviously, you don’t want to overspend on a system that’s more than you need. But, at the same time, buying a new air conditioner that can’t keep up with your home isn’t money well spent, either.

While brand reviews, warranties and service agreements are all important factors to consider, they are only really helpful once you’ve determined which products are the right size to do the job.

The two most important factors in determining the size of the air conditioner you need are going to be the size of your home and how much of your home you want covered. Cooling a bedroom in a small home or condo is a very different job that maintaining a pleasant temperature in a large house with an open floor plan. You’ll also want to take into account the average summer temperatures and common highs in your area. This will ensure that you have enough AC to take the heat (literally) when it comes.


BTUs (British Thermal Units) are the measurement used to determine an air conditioner’s cooling capacity, or how much heat it can pull from an area per hour. It’s also the measurement for your home’s heating system, as well.

Air conditioners of different sizes and capacities will have different BTU ratings. The higher the rating, the faster they can cool, and the more area they can handle. The typical recommendation is 20 BTUs per square foot of coverage. This means cooling an average size home will need a rating close to 12,500. The needs of a very large home with an open floor plan could run as high as 60,000 BTUs.

The amount of direct sunlight a room(s) get or if the exterior walls are shaded can play a factor, as will the typical occupancy. A large living room or family room will typically produce more body heat than a small kitchen, for example. Though, if there’s a lot of cooking done in that kitchen, and the living area is used infrequently, the impact could be completely the opposite.

Your location, again, will be a major consideration. For obvious reasons, AC needs are going to be very different in San Antonio than they are in Seattle.

This is why it’s just as important to factor in the unique characteristics of your home and lifestyle. Then, determine your cooling needs accordingly, as it is to map each room’s exact area.

Another measurement that’s often used in calculating AC levels is “Tons”, which correspond to BTUs. One “ton” is the equivalent of 12,000 BTUs. The same determining factors apply regardless of the rating system used.

Some other factors to consider include:

  • Condition of your ductwork
  • How well your home is insulated
  • How many people live in your home?
  • Heat-generating appliances like dryers, electronics, etc.
  • How many windows and exterior doors, and their condition?
  • How is your home constructed (brick, wood, other?)

Why Size Matters

When it comes to air conditioners, bigger isn’t necessarily better, but neither is smaller. Many folks use unit price as the key element in making their AC purchase, looking to save the most money upfront. Meanwhile, others are more concerned with getting the “biggest, baddest” unit on the market. Neither of these is ideal when deciding on a new air conditioner. The more important consideration here is efficiency.

Smaller AC units are likely to cost less than those with a higher BTU rating. But, the trade-off can be an air conditioner that has to run nearly constantly and still may not have enough “oomph” to cool your home to a comfortable level. In this case, the money that’s saved upfront (and more) is usually sucked up in higher electric bills.

Also, a constantly running unit is going to need more frequent servicing and will have a shorter overall lifespan.

On the other hand, if you have more AC than you need, that giant “DeepFreeze5000” unit will be switching on and off constantly, as it reaches its set temperature quickly and shuts down, allowing the house to warm back up fast, and…well…vicious circle.

The constant powering up and shutting down is just as hard on its components as the constant running of a too-small unit and, again, is going to increase energy use and utility costs, as well as shorten its life.

an air conditioning vent

How Long Do Air Conditioning Units Last?

In all fairness, this is a lot like asking how long a new car is going to last. There are a lot of considerations and outside factors that can affect lifespan. How often is the unit being used? Is it being cleaned? How often is professional maintenance being done? All these things affect when to replace your air conditioner.

Air conditioning technology and manufacturing improve every year. Better, more reliable components are being developed constantly.

Still, most of the answer is going to be determined by use and environment.

That said, for a good-quality, properly maintained unit, under typical conditions, the average lifespan quoted by most major manufacturers is 12 to 20 years.

The next question that comes to most consumers’ minds are, “How can I get the most life out of my new AC unit?”

Now, that is a question with some concrete answers…

  • Pick the right size AC for your needs
  • Minimize heat and cooling loss by sealing air leaks, especially in older homes
  • Invest in a “smart” thermostat
  • Schedule professional maintenance regularly
  • Keep air ducts cleaned and properly maintained
  • Use dehumidifiers to ease the load on your AC
  • Keep the area around your AC, especially the intake, clean and clutter-free
  • Use shades, awnings and other coverings to minimize direct sunlight on windows.
  • Replace incandescent bulbs with energy-efficient LED bulbs to produce less heat
  • Use ceiling fans to help distribute the cooler air and reduce loads on ACs

Given proper maintenance and responsible care, there’s no reason that you couldn’t get as many as 30 years of life from your new air conditioner.

Professional Service

Let’s face it, different people have different skill sets. You may be a mechanical wizard, or…not so much.

For most folks, the best value for service and regular maintenance of their AC unit is going to be to hire a professional. Professionals have the education, experience, and equipment to get the jobs done right. This saves homeowners hours of time researching, shopping and doing the physical work. Not only that but licensed professionals typically offer a guarantee on their work.

Also, going into your air-conditioner with your handy multi-tool will often void the warranty. You could also end up with costly repairs coming out of your pocket instead of the manufacturer’s.

Read your paperwork and call the manufacturer to confirm their policies before you end up sitting on the kitchen floor surrounded by air conditioner parts!

In fact, when shopping for a new AC unit, make sure that you read all that fine print. Many air conditioning companies offer complimentary inspections and even advice on picking the unit that will work best for your home.

a professional servicing an air conditioning unit

How Often to Service Air Conditioner

Your AC unit is there to help keep your home cool, and that need most often arises in the summer. This means, you do not want to wait until July to have your air conditioner serviced or worse, repaired.

Cleaning and simple maintenance can usually take a few hours. But, a newly diagnosed AC issue or the need to order a replacement part could leave you and your family sweating for days, waiting for it. This same advice works with your heating system as well. Don’t wait for that record-breaking snowstorm to get your heater serviced! A professional can help winterize your home and HVAC system.

When scheduling regular maintenance, early spring is probably the ideal time to get your air conditioner looked at. This way, any AC repairs can be completed before the intense heat sets in.

Whenever you get your air conditioner serviced, there are a few tasks you can expect your technician to perform during their visit:

  • A visual inspection of the unit or the entire HVAC system
  • Replacement of any air filters
  • Inspecting and cleaning all indoor and outdoor coils
  • Inspection of the condensate pump and cleaning of any dirt or debris
  • Checking the thermostat for proper function
  • Thoroughly cleaning of the system of any dust or debris
  • Detailed reporting and recommendations on any issues, or required replacements or repairs.

A professional AC technician can spot impending issues and deal with them, before they become major issues. This means less chance of expensive AC repairs and less chance of complete unit failure.

It’s also important to note that, even barring mechanical issues, unserviced air conditioners will lose 5% of their efficiency annually. This not only reduces their value and increases their usage costs, but can cut an AC unit’s lifespan by half!

In the long run, regular, professional service is not only going to ensure that your home and family are cool when things get hot, but it’s going to save you money as well. Your comfort and the comfort of your family are worth it.

ABC Can Keep Your Home Cool

Don’t lose your cool this summer. Contact ABC Home & Commercial Services for all of your air conditioning needs. If you’re in the market for an AC replacement, we offer complimentary inspections and honest advice on which system will work best for you. Additionally, we can provide any needed AC preventative maintenance and repairs.

Tom Riggs

Tom Riggs is the Division Manager for Mechanical Services, overseeing sales and operations for HVAC, Plumbing, Electrical, Appliance Repair and Water Quality for all ABC Austin branches. He joined ABC in 2014. Before ABC, he was an HVAC Service Technician, HVAC Comfort Advisor/Sales and Operations Manager. Tom attended Universal Technical Institute. He's an avid outdoorsman and enjoys country living with his wife and two sons.

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