So you’re ready to invest in central air conditioning? Congratulations! This is a purchase that will save you money and keep you comfortable for years to come. But whether you’re a first-time central air user or you’ve enjoyed it for years, you’re probably wondering what size AC unit you should get. Think of your air conditioner like a vehicle; you want the right size — with the proper amount of horsepower — for your unique needs. A general contractor won’t have much luck organizing their tools and equipment with a compact smart car. But a city dweller who spends much of their time searching for on-street parking certainly doesn’t need a full-size pickup truck! In this article, we’ll talk about choosing the best size ac unit for your home — and how to avoid overspending or under-investing.
Central AC units are measured by size with a unit called tonnage. Tonnage does not refer to their weight, but rather, your AC unit’s ability to cool air. For the math enthusiasts among us: One ton is equal to an air conditioner’s ability to cool 12,000 BTUs per hour. A BTU is a measure of energy; one BTU cools or heats one pound of water by one degree (in Fahrenheit). But really, what you need to know is this: The higher the tonnage, the more powerful the central AC unit.
Central air conditioners are measured by the half-ton. Typically, the sizing begins at 1.5 tons and, for residential usage, maxes out at 5 tons. It is not unheard of for a home to require a greater-than 5-ton AC unit, but in those instances your HVAC company will likely install multiple smaller-ton units. This strategy allows all areas of the house to receive maximum efficiency in cooling and is a more energy-efficient solution for the homeowner. It’s also a good preparedness strategy; if one AC unit breaks down, you’ll have a working backup plan. Houses with high square footage will require a large size AC unit, while smaller homes don’t need a high tonnage air conditioner. In other words: If a contractor proposes a 5-ton AC unit for your single-story, 600-square foot tiny home, run in the opposite direction!
With each passing year, technology gets smaller and smaller. If you need proof, just imagine slipping a cellular phone from the 1980s into your pocket. And generally speaking, the smaller and sleeker the machine, the more efficient and modern the tech. This is definitely true for air conditioners, so don’t get caught up in the “biggest is always best” mindset.
Unfortunately, there isn’t a magic formula using tonnage and square feet to determine the right size ac unit for your home. Some folks arrive at a rough estimate by multiplying their home’s square footage by 30, then dividing that number by 12,000 (there’s the BTU measurement), and finally subtracting 1. But there is so much more that goes into choosing what size ac unit you need, including your home’s flooring, outdoor shade situation, and the climate in which you live. This is where your local HVAC professional will be helpful; they’ll talk to you about the pros and cons of sizing up or down, based on your home size and energy usage.
If you install a small AC unit but your home really needs a high-tonnage AC, the air conditioner will run constantly. This is obviously an inefficient use of the technology and will reflect in a high energy bill during the hot months. You will also run the risk of overworking the air conditioner; the added stress may cause it to break down or require frequent maintenance.
On the other hand, if your AC unit is too big, it will actually be overly efficient. The air conditioner will moderate the temperature in your home quickly, before it completes a full cooling cycle. This causes it to turn off in the middle of the process and start up again a short time later. The constant hot-and-cold is a poor use of energy that will, again, result in unnecessary spending. Another downside of this consistent half-cycling is that the air conditioner won’t have time to adequately remove humidity from the air (remember that an AC unit cools air and conditions it). This could even result in mold issues in your home!
Think of your home like Goldilocks in the story of the Three Bears: You’re looking for an air conditioner size that’s just right! Contact a trusted professional to help you choose the best central AC for your home.
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