One important thing to do when you're building a new air conditioner system is to pick the right AC unit. When your air conditioner is too small, it won't cool the room properly. In more extreme cases, the unit could burn out quickly from over exertion. On the other hand, an air conditioner that is too powerful may be a waste of energy. Here are some steps for choosing the right size air conditioner. 

Calculate Square Feet of the Space

Your air conditioner's size will depend largely on the size of your home. You'll want to get out a tape measure and take the dimensions of your cooling area. If you plan on cooling the whole house, then it may be okay to do the dimensions of the entire home at once. 

Subtract Areas that Don't Need Cooling

Before you begin planning an HVAC air conditioning system, it's important to consider if you really need to cool all rooms of your home. There may be areas that you can leave out for a major energy savings. For instance, garages or other transitory spaces may not need to be included in your HVAC plan. You may even want to leave out your guest room in your HVAC system if it's not used often. For those rare times when you need to use the space, bring in a window AC unit. 

If you calculated your space based on the total volume of your home, measure the width and length of each room that you wish to subtract from the calculations. 

Calculate the BTUs Needed

BTUs, or British Thermal Units, are the measure of the cooling output on your AC system. There are a few ways to determine the BTUs needed to cool your home, but a good rule of thumb is to multiply the square footage by 25. 

Verify with an Expert

Before you go off of this estimate, it's always a good idea to run your calculations by an air conditioning services expert. There may be additional circumstances to consider. For instance, some HVAC specialists might have you add 10% to the BTU calculation for any room that gets a lot of direct sunlight. 

Once you have a good calculation for your air conditioner's BTU output, this will give you a good idea about the size of models you're looking for. If you are on the fence about any model, it may be good to go one size up, in case you add any space to your home in the future.