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How to Buy a Room Air Conditioner

Updated Apr. 18, 2017

Room air conditioners cool individual rooms instead of the entire buildings. They are usually installed in a window so that they can vent warm air directly outside without needing specialized ventilation. Because they cool smaller spaces, and can easily be installed by the buyer. As a final benefit, they are significantly cheaper than central air conditioners.

Recent models are quite energy-efficient. They come in different sizes and have varying cooling capacities that range from 5,000 BTUs (British thermal units) to 30,000 BTUs. The size of the air conditioner you buy will be determined by the size of the room you want to cool.

Choosing Your Room Air Conditioner

In addition to the size and capacity of your room air conditioner, other criteria to consider are:

  • The square footage of the room to be cooled: multiply the length of the room (in feet) by its width. How many BTUs you need to cool the room also depends on this.
  • Consider sun exposure, ceiling height, and insulation of the room and any additional floors or crawl spaces above or below the room.
  • Do you need room heating in addition to cooling? Some air conditioners have dehumidifiers and heaters built in, so you can use them in all seasons.
  • Warranty: Your room ac should come with a manufacturer's warranty of at least one year for parts and labor. You might also consider getting an extended warranty for an extra charge, although consumer groups generally suggest that extended warranties are not worth their cost.
  • The smaller the temperature increments the ac allows, the better the energy conservation. Look for 1-2 degree notches in the temperature settings. Digital controls allow for finer adjustments.
  • Look for an Energy Saver or sleep mode switch. With these, you can slow down the cooling process at night, which will conserve energy and reduce cost.
  • Slide-out Filter: since ac filters need to be cleaned regularly, choose an ac that has a slide-out filter instead of a frame enclosed one.
  • Fan-speed settings must be multiple for energy saving.
  • Installation: This should be an easy job. Some room air conditioners require that you drill a few holes for installation.

Air Conditioner Efficiency

The efficiency of a room air conditioner can be measured by the energy efficiency ratio (EER), which is the ratio of the cooling capacity (in BTUs per hour) to the power input (in watts). So the higher your EER rating, the more efficient your room ac will be. For example, if a 10,000-BTU air conditioner consumes 1,200 watts, its EER is 8.3 (10,000 BTU/1,200 watts). The higher EER produced, the higher priced the air conditioner is. Look for an ac that has an EER of 10 or more.

Calculating the Payback Period

The payback period is a calculation that can be used to compare two options. For example, the higher the efficiency of a particular air conditioner, the more expensive it will be. So one of the issues you should consider when deciding between a high and a low efficiency room air conditioner is the payback period for choosing the higher-efficiency model.

For example, suppose you are choosing between two similar air conditioners, one which costs $300 uses 1000 watts / hour to run, and a second which costs $450 uses only 800 watts per hour. The higher efficiency unit will cost you an extra $150 up front, but you'll save that cost in lower electricity bills over time. The question is, how long is the payback period for that extra $150?

The first step is to collect some information. First, how much does your electric utility charge per kilowatt/hour? This information will generally be printed on your electric bill. Second, how many watts / hour (or kilowatts / hour) do the air conditioners consume? Third, how many days out of the year do you expect to run your air conditioner, and fourth, how many hours per day on average? (Note, your predictions don't need to be exact -- you're just trying to get a reasonable estimate.)

Now for some basic math:

  • Convert each air conditioner's energy usage to kilowatt / hour, by dividing watts per hour by 1000. For example, the 1000 watts / hour is 1kWh, and 800 watts / hour is .8kWh.
  • Multiply the number of days per year by the number of hours per day to get an estimate of the number of hours per year you will use the air conditioner.
  • Now, multiply the kWh times the number of hours per year, to get the kWh / year.
  • Finally, multiply the kWh / year by the cost per kWh. This tells you how much each model will cost you per year.

So, let's suppose that you plan to use your air conditioner from May 15th to Sep 15th (about 120 days). And you think you'll average about 5 hours a day of usage. That means that you expect to consume about 600 hours of air conditioning. And let's further suppose that your electric utility charges $0.10 kWh. So for the less efficient model, you would use 600 x 1 kWh = 600 kWh of electricity / year, for a total cost of $60 per year. The more efficient model would cost you 600 x .8 = 480 kWh of electricity, for a total of $48 per year.

In this scenario, your payback period answers the question: how many years of using the more efficient air conditioner would it take to pay off the extra cost of that air conditioner? Since the more efficient unit saves you $12 / year, and you spend an extra $150 on it, the payback period is $150 / $12 = 12.5 years.

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