# Why Size Matters – Tonnage of units per size of houses

How do you know how big of an AC unit you need to have for your size home? Size Matters when it comes to air conditioning and there are a few factors that play into the size HVAC system that you will need, including ceiling height, insulation type and thickness as well as climate zone. You need to be sure your unit is not too big or too small in order to be sure your HVAC system is working toward your comfort safely and efficiently.

HVAC systems come in many sizes and are measured by “tonnage.” This does not refer to how much the unit actually weighs, but to the amount it is able to cool down efficiently. For every “ton” your HVAC system has the ability to cool 12,000 British Thermal Units or BTUs per hour. A BTU is the amount of energy required to raise or lower the temperature of one pound of water by one degree Fahrenheit. For example, a 1-ton HVAC Unit can cool 12,000 pounds of water by 1 degree every hour. Typical houses will need between 1 and 5-tons. More than 5-tons is usually considered a commercial unit. If your home is exceptionally large then considering running 2 smaller units at the same time may be your best option.

There is a simple equation to estimate the size tonnage you would need for your home. The area and climate you live in also plays a part in the size you would need.

Typically, you would take the House square footage and multiply it by 30 and divide it by 12,000 then subtract 1. For example, if you have a 1500 Sq. Foot home you would multiply 1500 x 30=45000. Then divide 45000 / 12000=3.75. Then subtract 3.75-1=2.75. Since HVAC units come in tonnage of halves you would need either a 2.5 or 3-ton unit. If you live in a particularly hot climate like Florida, or Southern California you would get a better estimate if you do not subtract at the end. In this case it would equal 3.75 and you would want a 3.5 or 4-ton unit to keep up with the heat and humidity.

Another way to calculate your tonnage is by using the following graph and chart. Find your Climate zone color and then coordinate it with the chart color and your homes square footage.