That Pesky Question

It’s the middle of the summer when your air conditioner breaks and the search for a new one begins.  No sooner are you online browsing before the same question hits every time: what size air conditioner do I need?  This question is absolutely crucial to anyone looking to purchase a new air conditioner for their home. If you have a house that is small and quaint then you wouldn’t want a large air conditioner that is heavy to carry and hard to install.  Establishing a budget early on and sticking to it is the best strategy to avoid buyers remorse.

Take a look at some of these top rated air conditioners of various sizes:

Quality Air Conditioners

NameFrigidaire FFRE0533Q1 5,000 BTU 115V Window-Mounted Mini-Compact Air Conditioner with Full-Function Remote Control
Frigidaire FFRE0833Q1 8,000 BTU 115V Window-Mounted Mini-Compact Air Conditioner with Temperature Sensing Remote Control
Frigidaire FFRE1233Q1 12,000 BTU 115V Window-Mounted Compact Air Conditioner with Temperature Sensing Remote Control
LG LW1215ER 12,000 BTU 115V Slide In-Out Chassis Air Conditioner with Remote Control
Product Dimensions15.2 x 16 x 12 inches15.5 x 18.5 x 13.4 inches21.5 x 19 x 14.5 inches22.2 x 23.6 x 15 inches
Shipping Weight46.4 pounds47 pounds82.6 pounds92.8 pounds
Item Model NumberFFRE0533Q1FFRE0833Q1FFRE1233Q1LW1215ER
Customer ratings4.2 out of 5 stars3.9 out of 5 stars4.2 out of 5 stars4.3 out of 5 stars

There are a number of things to consider when thinking about buying an air conditioner such as:

  • Budget
  • Size
  • Location/placement in your home
  • What does a professional say?
  • How will it affect my energy bill?

With all of these factors influencing your decision, the answers to those questions should help provide you with a good estimation of what size unit is right for your home. 

Don’t Go Too Big For Your Home

According to Angie Hicks of Angie’s List, an over-sized air conditioner can and most likely will experience short cycling periods. This means that the air conditioner will run long enough to cool the home, but is extremely inefficient at removing the humidity from the air.

An over-sized air conditioner is prone to spontaneous shut on and off which is a nightmare for energy efficiency, and accordingly, your wallet.   Making sure your unit is doing only the necessary amount of work, and not more, will save tremendous amounts of money on energy bills.

Don’t Go Too Small Either

According to ASM Air, even purchasing an air conditioner that’s too small will run all day constantly and never properly cool your home.  This can also lead to the unit malfunctioning early and having to spend more to replace the unit.        

What Size Air Conditioner Do I Need? I Want Numbers!

For those of you who want exact specifications to make absolutely sure that you’re getting the right size unit for your home, ASM Air also has a formula to calculate what size you need: House square footage times 25, divided by 12,000 – 0.5 = required tons. They also have another way to see what size you need because they have a chart for consumers to go by. For window air conditioners, this is a great option if you only want to cool a single room in the house and don’t want to spend money on a central air conditioning unit. The same concept of size matters with window air conditioners as well, according to Lowe’s. A air conditioner unit that is too small won’t cool your room efficiently and if it is too large the air will cool slightly but continue to feel sticky and damp..

The Numbers

These are the different sizes based on square footage:

    • 150 to 350 sq ft: look for a 5,000- to 8,000-BTU unit


    • 350 to 550 sq ft: look for an 8,000- to 12,000-BTU unit


    • 550 to 1,050 sq ft: look for a 12,000- to 18,500-BTU unit


    • 1,050 to 1,600 sq ft: look for an 18,500- to 25,000-BTU unit



Window Units

Specifically with window air conditioners there are also some points to consider before purchasing:

    • Have help when installing a window air conditioner because they are heavy.


    • Installing a window air conditioner in a window that won’t get direct sunlight is better.


    • Always make sure there is an adequate power outlet beside the window you want to install the air conditioner in.


    • Also make sure it is installed properly so it won’t collect water and freeze up.


According to Allison Bailes of Energy Vanguard Blog, the label tells you the model number and the serial number and this is what you can go by once you figure out how many tons your air conditioning unit needs to be. Bailes also had examples of how you can go by the model number to find the amount of tons:

Model Number – Tons

018 1.5
024 2
030 2.5
036 3
042 3.5
048 4
060 5

Other Sizing Factors

Another important factor in determining how big your air conditioning unit needs to be is British Thermal Units (BTU). These units tell you how much heat it will take to elevate the temperature of one pound of water by one degree Fahrenheit, according to Mary Mattoon of The number of BTU’s needed to cool your house depends on the amount of square footage you have in the home.

Professional Help

For people who want air conditioning units, but don’t want to do the calculations themselves, George Brazil HVAC states that you need a professional air conditioning technician to do a Manual J Heat Load Calculation. This calculation takes these factors into account:

  • Square footage
  • Layout (multiple levels, basement, etc.)
  • Number of windows
  • How shaded your roof, walls and home are
  • Where you have vaulted ceilings (if you do)
  • The quality of your home’s insulation
  • If your air ducts are sealed and insulated

Cool Down

Using all of the methods provided here will help you to pinpoint exactly what size air conditioner is best for your home.  Remember, having a unit that is too big or too small could cost you a fortune in the long run.  Happy savings!