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Buying Window Air Conditioners | How to Decide What You Need

Updated on April 21, 2014
Cre8tor profile image

Dan has been in the HVAC industry for 22 years with experience ranging from installation and service to sales and distribution.

What Size Air Conditioner Do You Need?

How much area can you cool? What do I need to go with it? What is tonnage?

All these questions and more will be answered here for you. Don't just guess at what unit "might work" or "seems right", know that the money you're about to spend on a window a/c unit is going to get you exactly what you need.

Let's start with a simple checklist of things you'll want to know before heading to the store or purchasing that unit online.

  • - How many square feet are you planning to cool?
  • - What size is the window opening in which you will place the unit?
  • - Do you have a support bracket or will you need one?
  • - What electrical voltage do you have or will the unit require?
  • - Will you need to direct the drainage from the unit?
  • - Terminology...will you understand what the ratings and specifications mean?

If some of this seems like a lot, it really isn't. I will help you understand in simple terms what all this means and even give you what you need to answer these questions.


Window A/C's Are an Easy Affordable Way to Cool

Cool your space quick and easy by purchasing the right window unit for you.
Cool your space quick and easy by purchasing the right window unit for you. | Source

Here's A Great Example Of A Common Unit Size With Great Features For Energy Efficiency Too

Sizing Your Window Air Conditioner

It is important to remember when sizing an air conditioner that bigger ISN'T better.

We're not talking about physical dimensions in this case. We are talking about cooling power "sizing" which is referred to in "BTU" or "tons". (12,000 BTU = 1 ton, 6,000 BTU = 1/2 ton)

When talking about air conditioning, what is really happening is the air is cooled greatly by de-humidifying the air. When a unit is too big, it will "short cycle" and proper de-humidification is never really achieved therefore increasing running costs and wear/tear on the unit.

When faced with a "borderline" decision on what size unit to buy, always go with the slightly smaller unit. You will save on energy and still cool the space very well.

With that in mind, the amount of square footage you're trying to cool will determine how many BTU you need. You can find this out by measuring the length and width of the room and then multiplying them. If you have a triangular section, separate it from the square measurements then measure the length and width of that area, multiply those and then divide it by 2.


BTU to Square Footage Reference Table

Space Size (sq. ft.)
BTU Needed to Cool
100-150
5,000
150-250
6,000
250-300
7,000
300-350
8,000
350-400
9,000
400-450
10.000
450-550
12,000
NOTE: If you have 460 square feet and can save money by purchasing the smaller unit, I suggest you do and feel confident you will still cool the area quite well.

How About You?

Would you have thought "bigger is better" if you weren't sure what A/C size to buy?

See results

Make Sure You Take the Maximum Measurement

Measure into the track for a true maximum measurement.
Measure into the track for a true maximum measurement. | Source

Measuring the Window Opening

When talking about the physical size of the window unit you're considering, it's really as simple as measuring the maximum opening of the window's height and width. What you want to keep in mind is that the unit will usually have an expansion kit to help fit various sizes. When looking at the unit, make sure it will expand far enough to go INTO the window tracks so that you don't have air leaks and get the added support of the expansion kit.

NOTE: Most units only expand horizontally. If you have vertical or "casement" windows, you will have to purchase a "casement" style window unit so that it is built for your need and provides expansion in the direction you need. If no expansion kit is available for your casement unit, you will want to look into purchasing some plexi-glass or perhaps even some cheap and easy to cut foam insulation board to fill the empty space above the unit.

Heavy Duty and Simple to Install Window Support Bracket

Installing the Window A/C Unit With Proper Support

Installing a window air conditioner is usually quite simple however you want to be sure you have the proper support system in place so that you don't risk the unit falling out unexpectedly.

Make sure you've chosen a good window for your unit. You don't want to chose one that the framing itself isn't trustworthy to hold the weight of the unit or support bracket that you will be installing.

Buying Used Window A/Cs

If you're buying a used window air conditioner, don't just plug it in and determine that it's functional. Problems will not usually show themselves until the unit has ran for at least 10 minutes and repairs are not cheap thus defeating the point of buying a used unit.

Window Air Conditioning Voltage

There are 2 common voltages at which residential window air conditioners operate at. 110/120V and 220/240V are those options.

Nowadays most units can operate on a standard 110/120V receptacle. This is great because it's just a plug and play scenario however, there are still some units out there that require a 220/240V power source.

Usually, you will notice a difference between a standard 110/120V receptacle and a 220/240V receptacle but if you can't, there are a couple easy ways to make this determination.

  1. Test the voltage with a voltmeter if you have one.
  2. Check your breaker box. There will be a dedicated "2 pole" breaker for that window unit receptacle. (A 2 pole breaker will be noticeably bigger than your other breakers taking up 2 spaces in the box and will likely be marked for a higher amperage than others too.)

DO NOT TRY TO RUN A WINDOW UNIT ON THE WRONG VOLTAGE. You will either damage the unit beyond repair or cause a hazardous situation.

Window Air Conditioners Drain

As I mentioned, air conditioners are also dehumidifiers. Knowing this, all dehumidifiers need to drain off the humidity they are removing from the air.

You've probably noticed that window air conditioners drip. This is their way of draining and why you have to slightly tip the unit outwardly from the home to avoid that drainage from coming into the house or seeping down into the framing of the window.

I say all that to say this...be mindful of where your a/c unit will be draining to. If it will be dripping down onto the neighbor's patio, you may want to fasten a piece of aluminum or similar to divert the drainage away from that area. Granted, there may be only so much you can do but be cognoscente of the fact that this is happening.

Air Conditioning Terminology

As you begin to shop for your window cooling unit, you may notice some terms that though you recognize, may not fully understand. Here are a few of the more common terms that seem to be asked about in my 19 years of experience.

  • Ton - Tons are used to describe the cooling capacity of an a/c unit. Back when ice was used to provide cooling, it was based on how many tons of ice would have to be melted in a 24 hour period to provide enough cooling. The term has just stuck over the years. This then can be translated into BTU and vice versa. 12,000 BTUs equal 1 ton. Therefore, it would've taken 1 ton of ice per day to cool a 500 square foot area. Pretty cool fun fact eh?
  • BTU - A BTU or British Thermal Unit is the term used to describe how much energy it will take to raise the temperature of 1 pound of water, 1 degree. This is again just a sort of fun fact but gives you a better understanding of what these terms are. Again, for you, matching up the proper BTU to square footage ratio is what's important and we've already done the math for you.
  • Condensation - When talking about air conditioning, condensation is what is being drained off of the unit or the dripping you see from them. When you watch an a/c system of any sort work properly, you'll notice the copper lines of the evaporator coil sweating. This is the humidity that is being removed building up on those lines.
  • SEER / EER - SEER or EER stands for (Seasonal) Energy Efficiency Ratio. By today's standards, a 10 SEER rating on a window a/c unit is pretty good.

A Few Parting Thoughts

I would like to leave you with a few more things that I've found to be true and/or helpful to those who use window air conditioners.

  1. Make sure you maintain and store the unit properly. This will increase the lifespan of the unit significantly. Many of those units that end up in the "graveyard" are there because they were not properly stored. NEVER run a unit that has been stood up on it's side. You must set the unit as it would be when installed so that the oil in the compressor drains down to where it should be or it will damage the compressor when ran. Let it set that way for a few hours before running if it has been stored this way.
  2. If placed in a good spot, a window unit can provide at least some cooling to the surrounding areas beyond the square footage it's rated to cool. Especially if you place a fan in front of that area to pull the cool air out and disperse it into a hallway or such where other doors are open.
  3. Place small rags, hand towels or something of that nature around the unit so that it protects your window sills and framing as well as preventing any hot air leaking in around small gaps where the unit is installed.
  4. Units with timers and remotes are a nice convenience and offer significant savings. Since bedrooms are a popular place to install these units, a remote is a real nice feature for those nights where it gets a little to cool and you don't want to have to get up to tinker with the settings. The timers and/or thermostat options are nice too so that you can program the unit to turn off and on a times or temperatures when you are not there to do so manually. This can save you a nice amount of money as well. (Intermittent fan options during off cycles is another real nice feature if available.

Stay cool this summer!

© 2014 Dan Robbins

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    • Kristen Howe profile image

      Kristen Howe 

      3 years ago from Northeast Ohio

      Daniel, this is super useful and timely for this hub. Voted up!

    • Cre8tor profile imageAUTHOR

      Dan Robbins 

      4 years ago from Ohio

      Thanks WF! Of course I'm biased by trade but I agree, air conditioning is one of the greatest inventions and it's way underrated when people begin to list their necessities like electric, water, etc... in preparation for "doomsday". The history of refrigeration is where it begins. A/C as we know it was a "fringe benefit". It's really cool to see how those who lived in warmer climates prior to electricity made ice.

    • Writer Fox profile image

      Writer Fox 

      4 years ago from the wadi near the little river

      I think air conditioners are one of man's greatest inventions. Can't imagine life without them. Great article with great advice. Enjoyed and voted up!

    • Cre8tor profile imageAUTHOR

      Dan Robbins 

      4 years ago from Ohio

      Thank you kindly grand old lady! I'm glad you found it helpful and I hope it will be to others as well.

    • grand old lady profile image

      Mona Sabalones Gonzalez 

      4 years ago from Philippines

      Very useful tips in deciding what is the right air conditioner for you. In a tropical country like the Philippines, a hub like this is most useful.

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