Why HVAC Sizing Matters: The Goldilocks Problem

HVAC sizing isn't about getting the biggest system you can afford. Like the fairytale, you need the size that's "just right."

The Problems with Oversizing

An oversized system: - Cycles on and off frequently (short cycling) - Doesn't run long enough to dehumidify - Creates temperature swings - Wears out faster from constant starting - Costs more upfront for capacity you don't need

Despite intuition, a bigger AC doesn't cool better—it cools too fast and shuts off.

The Problems with Undersizing

An undersized system: - Runs constantly on extreme days - Can't maintain comfortable temperatures when you need it most - Works harder, potentially shortening its life - May struggle with humidity control

The Just-Right Size

Properly sized equipment: - Runs in longer, more efficient cycles - Maintains consistent temperatures - Dehumidifies effectively - Lasts longer with less stress

How Sizing Should Be Determined

Manual J Load Calculation The industry standard. A proper load calculation considers: - Square footage - Ceiling heights - Window area, type, and orientation - Insulation levels - Duct efficiency - Number of occupants - Local climate data

Software performs these calculations to determine required capacity in BTUs or tons.

What's NOT Adequate - "Same size as your old one" (especially if you've made home improvements) - Rule of thumb like "1 ton per 500 sq ft" - Quick estimates without measuring or inspecting

Two-Stage and Variable Speed Modern equipment can adjust output, providing some buffer for sizing. But they still need to be in the right ballpark.

During Replacement

If getting a new system: - Insist on a load calculation - Ask about the sizing methodology - Be skeptical of quick quotes without inspection - Recognize that the right size might be different from your old system

If your home has been improved (new windows, added insulation), you might need smaller equipment.