How to Properly Size an AC Unit for Your Home

When it comes to choosing the right AC unit, most homeowners assume it's based on square footage alone—but that’s a common misconception. Proper AC sizing depends on cubic footage, not just square footage. Why? Because air volume, insulation, ceiling height, and airflow (CFM) all play a crucial role in determining the correct system size.

Improper AC sizing can lead to:
❌ High energy bills from excessive cycling
❌ Poor humidity control, increasing mold risks
❌ Uneven cooling, causing discomfort
❌ Shortened AC lifespan due to stress on components

Let’s break down how AC sizing really works and why CFM (Cubic Feet per Minute) is the key to ensuring your home stays cool and efficient.

Why Square Footage Isn’t Enough

Most people assume a “rule of thumb” approach—like 1 ton of cooling per 500 square feet—is accurate. But this ignores critical factors like:
✔️ Ceiling height – A home with 8-ft ceilings vs. 12-ft ceilings has drastically different cooling needs.
✔️ Insulation & Windows – Poor insulation or large windows can let heat in, requiring a stronger AC.
✔️ Ductwork & Airflow – Proper air circulation is key to cooling efficiency.

Instead of relying on square footage alone, HVAC professionals size AC units based on cubic feet of air that needs cooling.

What is CFM, and Why Does It Matter?

CFM (Cubic Feet per Minute) measures how much airflow an AC system can handle. Proper airflow ensures:
✅ Even cooling throughout your home
✅ Efficient humidity removal
✅ Optimal energy performance

The general rule is 1 CFM per square foot, but ceiling height directly impacts the total cubic feet of air that must be cooled.

🔹 Example: A 1,500 sq. ft. home with 8-ft ceilings contains 12,000 cubic feet of air.
🔹 A 1,500 sq. ft. home with 10-ft ceilings contains 15,000 cubic feet of air—a 25% increase in cooling demand!

If airflow is insufficient, the AC won't dehumidify properly, leading to mold growth and discomfort. If airflow is too strong, it short cycles and wastes energy.

How to Properly Size Your AC Unit

HVAC professionals use Manual J Load Calculations, factoring in:
📌 Home’s cubic footage (not just square footage!)
📌 Climate & sun exposure
📌 Insulation, windows, and ventilation
📌 Duct design & CFM requirements

An AC system should be sized just right—not too big and not too small—to maximize efficiency and comfort.

Need Help Sizing Your AC?

At FL HVAC Services, we use precise calculations (Manual J)—not guesswork—to ensure your AC unit is properly sized for maximum comfort, efficiency, and longevity.

📞 Call us today 352-358-5537 to schedule a professional AC assessment!