Choosing the wrong AC size wastes money and shortens equipment life. An undersized unit runs nonstop and never reaches comfort, while an oversized unit short cycles, leaves humidity high, and wears out faster. Proper sizing starts with a load calculation, not a rule of thumb.
Underwood Heating & Air Conditioning provides Manual J load calculations for homes across Phenix City, Auburn, Opelika, and East Alabama. We size your system to match your home, insulation, window exposure, and local climate.
Published: February 27, 2026 • Last updated: February 27, 2026
AC sizing is measured in tons (1 ton = 12,000 BTU/hr). A proper load calculation considers square footage, insulation quality, window count and orientation, ductwork condition, ceiling height, and local humidity levels. East Alabama's high humidity makes accurate sizing especially important.
Symptoms: Cycles too quickly, high indoor humidity, uneven room temperatures, and higher energy bills than expected.
DIY check: Check if the AC runs less than 10 minutes per cycle and the house feels clammy even when cool.
Professional fix: Perform Manual J load calculation. If significantly oversized, right-size at next replacement for better comfort and efficiency.
Symptoms: System runs constantly during hot days, never reaches set temperature, high energy consumption.
DIY check: Note if the system struggles to reach setpoint by mid-afternoon on hot days (above 90°F).
Professional fix: Verify sizing with load calculation. If undersized, evaluate whether ductwork and insulation improvements can help or if upsizing is needed.
Symptoms: Even a correctly sized AC struggles because heat gain exceeds design conditions due to insulation gaps.
DIY check: Check attic insulation depth. Many older East Alabama homes have less than R-30 in the attic.
Professional fix: Recommend insulation improvements and recalculate load to determine if the current system is adequate with better insulation.
Symptoms: Some rooms are much warmer than others, system runs long cycles, and attic or crawlspace feels cold.
DIY check: Visually inspect accessible ductwork for gaps, disconnections, or crushed flex runs.
Professional fix: Duct pressure test, seal all leaks, and verify balanced airflow to every room.
Symptoms: Rooms with large or west-facing windows overheat in the afternoon despite the AC running.
DIY check: Note which rooms are hottest and whether they have large, unshaded windows facing south or west.
Professional fix: Include window orientation and shading in load calculation. May recommend window treatments or zoning.
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Step 1: Is your AC running constantly but not reaching the set temperature?
If yes: The system may be undersized or losing capacity. Schedule a load calculation and system evaluation.
If no: Go to Step 2.
Step 2: Does your AC cool the house quickly but leave it feeling humid or clammy?
If yes: The system may be oversized. A load calculation can confirm and guide your next equipment decision.
If no: Go to Step 3.
Step 3: Are some rooms significantly hotter than others?
If yes: Ductwork or insulation issues may be reducing delivered cooling. Schedule a duct and airflow evaluation.
If no: Go to Step 4.
Step 4: Are you planning to replace your AC soon?
If yes: Request a Manual J load calculation before selecting new equipment. This ensures proper sizing.
If no: If your current system is comfortable and efficient, sizing may be fine. Schedule maintenance to keep it that way.
Find the model number on your outdoor unit nameplate. The tonnage is often encoded in the model number (18 = 1.5 ton, 24 = 2 ton, 30 = 2.5 ton, 36 = 3 ton, 48 = 4 ton, 60 = 5 ton).
Normal cycles run 10-20 minutes. Very short cycles (under 10 min) suggest oversizing. Nonstop running on a 95°F day may be normal but warrants evaluation if you never reach setpoint.
If your home feels clammy even when the AC is running, the system may be oversized and not running long enough to remove humidity.
Insulation directly affects how much cooling your home needs. Thin or damaged insulation increases the load on your AC system.
Caution: Use caution in attics during summer. East Alabama attic temperatures can exceed 140°F.
A load calculation is included with installation consultations so you never pay for guesswork.
Equipment pricing depends on the system size, efficiency rating, and installation complexity. We present options so you can choose what fits your budget.
We do not push the largest system—we recommend the right size for your home and comfort preferences.
AC sizing consultations and load calculations are available across Phenix City, Auburn, Opelika, and nearby East Alabama communities.
A Manual J load calculation determines the correct size based on your home's square footage, insulation, windows, layout, and local climate conditions.
An oversized AC short cycles, wastes energy, leaves humidity high, and wears out faster. Proper sizing provides better comfort and lower bills.
An undersized AC runs constantly, never reaches the set temperature on hot days, and creates excessive wear on the compressor.
No. Insulation quality, window count and orientation, ceiling height, ductwork condition, and local humidity all affect the required capacity.
Rules of thumb are unreliable. A 2,000 sq ft home might need 3 to 5 tons depending on insulation, windows, and construction. A load calculation gives the accurate answer.
Yes. High humidity increases latent load, which means your AC needs to remove more moisture. Proper sizing ensures the system runs long enough to dehumidify effectively.
Load calculations are included with installation consultations. We want you to have accurate sizing data before making any equipment decision.
Yes. Better insulation reduces heat gain, which can allow a smaller, more efficient AC system that costs less to operate.
Call for fast local help. We diagnose first, explain your options clearly, and restore comfort as quickly as possible.
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