What is Important When Buying a New Room Air Conditioner

This is for Jen.

Earlier this week was the hottest day in our area all year – by far – and it was only June.  That day I was picking my kids up from my friend’s house, and she told me that her air conditioner had decided to leap to its death – literally.   Jen said that a few minutes after she got home, she heard a weird scraping and banging noise from upstairs/outside.   When she went outside to see what was going on,  her air conditioner was hanging out of her 2nd floor bedroom window,  held up only by the power cord.   Within a few minutes, it fell to the ground, and died.  Like I said, it literally jumped to its death.

Now, maybe I should write a post about air conditioner safety,  but really, neither of us actually knows why it came out of the window.   Had a kid been messing with it?  Or her cat?  No clue.  Be sure to read the instructions and install your air conditioners properly.  Every year.  In fact, consider taping the instructions to the top or side so you don’t lose them.  Whatever the reason was, she definitely needs to buy a new A/C, and I bet she’s not the only one who could use some pointers.

We live in New England, and up here you don’t need air conditioning all the time, if your house is shaded with trees, then you can probably get buy with window fans most, if not all, of the time.  However, there are reasons you might want an A/C and central air isn’t the right answer.  Honestly, we have 4 room air conditioners in our house and I don’t think we could live without them.

There are a few things to know when buying an air conditioner:

Buy the Right Size Air Conditioner

Size? size?  It needs to fit in the window, right?   Yes, but more importantly, you need to know how to choose the right number of “BTUs” you want for your A/C.  The main thing that determines this is the size of the space you want to cool with the unit. 

standard room air conditioner
This is a BIG A/C, but it cools two rooms totally about 800 sqft

Not too big: Air conditioners de-humidify as well as cool.  If the A/C is too big (too many BTUs), then it won’t have a chance to properly dehumidify the room by the time the room reaches the correct temperature, and the room will still be uncomfortable.  Don’t be fooled by advertising that says “cools up to 1,000 sq foot room” – if your room is only 500 square feet, the A/C won’t function properly for your space.  It will also cycle on an off more frequently than desired, therefore reducing its energy efficiency.  As A/C units get bigger, they also get heavier making them harder to transport, store and install.

Not too small: If the A/C is too small (too few BTUs), it will take an unreasonably long time to cool the space, and may never cool it sufficiently on very hot days.

Measure the room: Before you go shopping, measure the space you want cooled.  You need to know the size of the room in square feet to know what “size” A/C you need.   The chart below (from the EPA) gives a conversion for the size of the room to the number of BTU you need.  If you have high ceilings, you are going to need to make adjustments for that too.  If you have 10 foot ceilings instead of the standard 8 foot ceilings, then you should get a bigger unit with 25% more BTU/hour.ruler

Area To Be Cooled (square feet) Capacity Needed (BTUs per hour)
100 up to 150 5,000
150 up to 250 6,000
250 up to 300 7,000
300 up to 350 8,000
350 up to 400 9,000
400 up to 450 10,000
450 up to 550 12,000
550 up to 700 14,000
700 up to 1,000 18,000
1,000 up to 1,200 21,000
1,200 up to 1,400 23,000
1,400 up to 1,500 24,000
1,500 up to 2,000 30,000
2,000 up to 2,500 34,000

Consider the use of the room: If the room is a kitchen, the EPA suggests adding an additional 4,000 BTU to what you need for the size of the room.    You may also need more BTU if many people frequently occupy the room or if it gets a lot of natural sunlight.

Measure the window: There is nothing more irritating than getting home with an A/C that doesn’t fit in the window.  Windows and A/Cs are usually a “standard size” but in New England, we have a lot of oddly shaped windows

Buy an Energy Star Air Conditioner

Energy Star Logo

Do you like to spend extra money on energy?  Neither do I.  Having the Energy Star label on a product means that it uses energy efficiently.  For different types of products this actually means different things.  Room air conditioners with the Energy Star label:

  • use about 10% less energy than conventional models, which could mean a savings of more than $60 over the lifetime of the unit.
  • often include timers for better temperature control, allowing you to use the minimum amount of energy you need to cool your room.

Consider additional features:

Consider if spending a little more on each of these features is worth it for the room in which you will use the A/C.

  • Remote Control – If the A/C is installed in a hard to reach window, or across the room from where you usually are, consider getting a model with a remote control.  For our bedroom, we have a remote that we can operate to adjust the unit from bed, but the kids don’t need that.  If you get a remote, consider taping it to the unit or putting it in a ziploc bag with other parts and taping that to the A/C when you store it for the winter.
  • Timer – a timer can be a really useful feature both in turning off and turning on a window A/C unit.  We have a timer on the unit in our living room that we have in the past set to turn on a little while before we get home so the house isn’t so hot when we come home.  The insulation and air sealing we did has made that less of an issue, but who wants to come home to an uncomfortable home if you can help it and we’d never leave it on the whole day while we were not home.  These are usually very basic timers that can be set to turn on or off in some number of hours. 

ceiling fan with LED lights
Fans make it feel 10°F cooler

And probably the best advice on air conditioners is to only use them when necessary and use a fan to make a space more comfortable with or without A/C.  A fan can make a room feel about 10°F cooler so you can set the A/C temp higher and use it less.

Happy Greening!


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  1. Thanks for sharing the information. Keep it up.


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