Air Conditioner Sizing is a Critical Factor in AC Selection

Air Conditioner sizing is the most important consideration when selecting an air conditioner. Unfortunately it is often not given much thought at all and this can cause problems later when the unit is in operation. This is not something you want to guess at.

Proper air conditioner size can be determined by using our air conditioner sizing calculator in the right column. This air conditioner load calculator is designed for determining what size window, portable or ductless air conditioner you need.

An HVAC contractor should do load calculations for central air conditioning because there are many variables that need to be factored in. This air conditioner btu calculator can be used to give you an idea of what size central ac unit may be needed but it could easily be off by a considerable amount.

These problems cannot be corrected after the equipment is installed. That is why the first question to ask yourself before shopping for a new air conditioning unit is what size air conditioner do I need?

Air conditioner sizes are determined by measuring their cooling capacity in BTU's per hour (British Thermal Units). A BTU is defined as the amount of heat required to raise the temperature of one pound of water one-degree Fahrenheit. All heating and cooling loads are based on this calculation. Load calculations in metric are done in calories.

It is common for people to buy an air conditioner that has too much cooling capacity, thinking that it will do a better job or perhaps it is better to have an air conditioner that is too big rather than one that is too small.

Some suppliers encourage this by suggesting that you purchase the maximum BTU rated air conditioner available and a dehumidifier to go with it. There are several reasons why this may not be a good idea.

An air conditioner that is oversized will not operate as efficiently as one that is properly sized. It is important to size a room air conditioner based on the estimated load that the unit will have to manage.

A properly sized air conditioner will also help to dehumidify the space that it is cooling. While the air conditioner is in operation the evaporator is cool and causes moisture to condense on the tubing surface. This is the same principal of operation as a dehumidifier.

An air conditioner that is oversized can short cycle. This means that the compressor will cycle off and on too often. When this happens it is difficult for the compressor to restart because the operating pressures within the air conditioning unit haven't had enough time to equalize. This can cause fuses to fail, circuit breakers to trip and compressor and overloads to eventually fail.