How do i know what size hvac unit to buy?

To calculate the size of air conditioner you need for a room, first multiply the length of the room by its width. Then multiply it by 25 BTUs to get sufficient cooling for the room in different weather conditions. For example, if the room is 15 feet long and 12 feet wide, that's 180 square feet. The good news is that most manufacturers of heating, ventilation and air conditioning systems make it easy to determine the rated capacity of your air conditioner.

Go out and find the outdoor unit, that metallic noise generator hidden on the side or in the back of the house. It will look something similar to the one you see above, although perhaps not as decrepit as that. Next, look for the label that contains the data about your air conditioner. It will look like in the image below.

One of the main deciding factors will be the square footage of the space you need to cool. However, this is not as simple as it seems. The Manual J calculation is what HVAC professionals in the industry use to calculate the size of the unit you need. So what size HVAC unit should you choose for the size of your home? For a single HVAC unit of what size, what matters most is in what area of the house it will be installed and in what temperature range it is desired.