One of the biggest mistakes I see homeowners make is picking the wrong size air conditioner. It’s not just about cooling — it’s about efficiency, comfort, and long-term savings.
I’m Tony, your trusted HVAC tech, here to walk you through what you need to know about sizing your AC right the first time.
Why Sizing Matters
Choosing an AC that’s too small means it’ll run constantly, struggle to cool your home, and rack up your electric bill. Too big? It’ll cycle on and off too frequently, causing uneven temperatures, increased wear, and poor humidity control.
The sweet spot is getting the right tonnage — measured in tons, where one ton equals 12,000 BTUs per hour.
What Factors Affect Your AC Size?
Several factors determine how much cooling power you actually need:
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Square footage of your home — The bigger the space, the more cooling needed.
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Climate — Hotter areas require more capacity.
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Home insulation and air sealing — Tight, well-insulated homes need less cooling power.
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Number of windows and sun exposure — More windows and direct sun increase cooling loads.
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Ceiling height — Higher ceilings mean more air to cool.
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Number of occupants and heat-generating appliances — More people and devices = more heat.
The Basic Rule of Thumb
A rough starting point is:
20 BTUs per square foot
So, if you have a 2,000 square foot house, you’d need roughly:
2,000 sq ft x 20 BTUs = 40,000 BTUs, or about 3.3 tons.
Keep in mind this is just a ballpark. For precision, you want a Manual J load calculation (more on that below).
How to Get a Precise Load Calculation
The best way to size your AC is with a Manual J load calculation, a detailed analysis done by a qualified HVAC professional.
It factors in all the elements above, plus:
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Construction materials
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Ductwork design
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Local weather data
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Ventilation requirements
This calculation ensures your system isn’t over- or under-sized.
Handy Tools for Homeowners
If you want to get an idea before calling a pro, you can use online calculators like:
These tools are great starting points but won’t replace a professional assessment.
Tony’s Pro Tip
Don’t trust random internet quizzes or rules of thumb alone. Getting a professional Manual J load calculation might seem like a hassle — but it pays for itself in energy savings, comfort, and system longevity.
A correctly sized AC means fewer repairs, lower bills, and a happier home.
Ready to Pick Your System?
Check out this versatile, energy-efficient option that pairs well with a properly sized air handler:
🔗 Goodman 3 Ton 14.5 SEER2 R-32 Air Conditioner and Air Handler System
