Choosing an air conditioning unit that is the right size for your home will keep you and your family comfortable all summer long, but you should avoid falling into the trap of thinking that bigger is better. If you purchase an air conditioner that is too powerful, it will turn on and off frequently and cool in short bursts. All of that switching on and off leads to uneven heating and humidity issues, and it can also shorten the life of an air conditioning unit. If you choose an air conditioning system that is not powerful enough, it will run constantly as it struggles to cool your home. This will result in higher energy bills and a home that is not nearly as comfortable as it could be.
BTUs, Tonnage and SEER Ratings
Air conditioner ratings are based on either British thermal units per hour or tons, but these figures do not refer to a unit’s physical dimensions or weight. Instead, they are measurements of how efficiently an air conditioning unit can remove heat. A British thermal unit is the amount of energy needed to increase the temperature of one pound of water by one degree Fahrenheit. Tons refers to the amount of hot air that an air conditioning unit can remove from a home in one hour.
BTUs and tonnage ratings will tell you how much heat an air conditioning system will remove, but they do not provide consumers with all of the information they need to make wise decisions. To fill this information gap, the federal government introduced Seasonal Energy Efficiency Ratios. A SEER rating lets consumers know how much energy an air conditioning unit will use during an average cooling season. More efficient units have higher SEER ratings. If you want to cool your home as efficiently and affordably as possible, you will need to find an air conditioning unit with a high SEER rating that is powerful enough to do the job.
Square Footage
Square footage calculations are the first thing HVAC professionals do when they are asked to design an air conditioning system. If you know your home’s square footage, you can multiply that figure by 20 to calculate the number of BTUs you will need to keep it cool. You can then convert the BTU figure into a tonnage rating by dividing it by 12,000. If your home is 2,000 square feet, you will need an air conditioning unit that is rated at approximately 40,000 BTUs and about 3.3 tons.
Other Factors
BTU or tonnage calculations based on your home’s square footage will provide you with a basic idea of how much cooling capacity you will need, but they will not tell you the whole story. Every home is different, which means every home has different needs. Let’s take a look at some of the factors other than square footage that could increase or decrease your air conditioner’s workload:
- Ceiling heights: Square footage figures provide a two-dimensional measurement of a three-dimensional space. If your home has high ceilings, you will need a more powerful air conditioner.
- Windows: About three-quarters of the sunlight that falls on your windows will enter your home as heat. If your home has a lot of windows or very large windows, your air conditioner will have much more work to do.
- Insulation: The insulation in your walls and around your doors and windows can significantly increase or decrease your cooling needs.
- Household size: Large households need more powerful air conditioners because people generate body heat and use appliances that increase interior temperatures.
- Shade: Homes that receive a lot of direct sunlight get much hotter, which means cooling them down uses more energy.
Manual J Calculations
Basic square footage calculations are often not enough to determine how much cooling capacity a home needs, so the Air Conditioning Contractors of America developed the Manual J load sizing protocol. This approach bases cooling needs on factors like ceiling height, room size, and sunlight as well as square footage, and it is used by just about all HVAC professionals.
Experience You Can Count On
If you would like to keep your home cool and comfortable and your energy bills under control, you will need an air conditioning system that is powerful enough but not too powerful. You can get a rough idea of how much cooling capacity you will need by doing some basic square footage calculations, but you may need a more powerful system if your home has high ceilings or lots of large windows. If you want to take the guesswork out of planning an air conditioning system, you can ask the friendly HVAC professionals at One Hour Air Conditioning & Heating to visit your home and complete a Manual J calculation. Additionally, consider exploring ways to reduce your energy costs with a new AC.
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