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Purchasing the Correct Sized Air Conditioning

Whether you require a new Air Conditioning Unit or it is time to replace your old system, it is imperative that you purchase a unit that is large enough to cool the space that you want.  Air conditioning units are measured in BTU’s (British thermal units), the greater a units BTU the greater the space it will cool.  BTU's are addressed below. 

There are several problems that you can face if you do not choose the right size air conditioning unit for your space. Believe it or not a bigger unit does not necessarily mean that you will be paying more money in electricity; it may actually mean that your cooling system will be more efficient thereby saving you money in the long run. 

Calculate air conditioning requirements

Why Not Just Go Big?

It would seem that you could not go wrong with just buying the largest unit you could find. While this seems reasonable it is actually a huge waste of energy. Air conditioning units have two functions. The first function is to reduce the humidity in the room. The second is to cool the room. 

A larger than necessary unit will quickly cool the room but will do it so quickly that the unit will not adequately remove the humidity. You will be left with a room that feels damp not comfortable. You may also be left with a higher electric bill if the unit is larger than needed.

If You Go Small

Buying a unit that is too small to cool your space is just as bad as going too big. If the unit does not have enough BTU's it will continually run. This is because air conditioners have an internal thermostat that is supposed to shut the air conditioner off when the space reaches a certain temperature.  Of course the fact that the unit will continue to run, runs up the electric bill. 

Understanding What You Are Buying 

If you have never purchased an air conditioner before purchasing the correct sized air conditioning unit may seem a little daunting but if you understand what you are looking at when you are looking at your options it will make it a lot less daunting and a lot less stressful. 

As mentioned before, BTU’s are a traditional measure that is used to determine how much energy is needed to cool or heat water by one degree in either direction.   This unit of measure has largely been replaced except in air conditioning and heating applications. 

The more BTU's a unit offers the greater the space it will cool. All you need to do to effectively choose the right unit is to know how much square feet you will be cooling. There are several different types of units as well. Once you determine the square footage of the area that you will be cooling than it is time to decide which type of unit you will need. 

Doing the Math 

BTU/ph = Flow Rate (in Gallons per Minute) x 
​[Temperature Leaving Process - Temperature Entering Process] x500

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Lets say that up to 150 square feet needs to be cooled, you would need a unit that offers 5,000 BTU's per hour. Sounds simple enough but there are other variables that you will need to consider. If more than 2 people use the space than you need to up the BTU requirements by 600 BTU's per person. If the room is particularly sunny than add another 10% on to the BTU requirement. If the room is primarily shady than you can reduce your BTU requirements by 10%. If the unit is going to be mounted in a kitchen or another area that constantly has a running heat source than you need to up the BTU requirements by about 4,000. 

Most units are clearly marked with the expected amount of square feet that it can cool. If you follow the guide lines above and consider the other variables of your space than you should be confident in your ability in purchasing the correct sized air conditioning! 

Most Popular Units 

For smaller spaces that can be cordoned off via a door from the rest of the house or business, a window unit is the unit of choice. A window unit is easy to install and can be moved from room to room simply by taking the unit out of one window and installing in another. 

The drawback of a window unit is that it would never be quite large enough to cool an entire home or an entire apartment. They also need to be installed where they are able to drain. All air conditioning units build up condensation which has to drain somewhere. 

Portable units are also an option for a smallish space. Portable units can be both vented and without vents. The vented type usually needs to be placed near a window where a hose that is attached to the unit can be placed outside the window to drain. 

Ventless portable units have trays that are built in the bottom that have to be emptied daily. 

For more advice on calculating your air conditioning requirements pleae contact us at

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