Why AC Sizing Matters More in Georgetown Than Most Texas Cities
Georgetown TX has a design temperature of 101°F — the outdoor temperature used for HVAC system sizing calculations. This is significantly hotter than cities like Dallas (100°F), San Antonio (99°F), and far hotter than most national averages. This 1–2°F difference doesn't sound significant, but it changes system sizing recommendations by 0.5–1 ton in many Georgetown homes.
The result of undersizing: a system that runs 100% of the time on peak summer days and never reaches your thermostat setpoint. This isn't just uncomfortable — it's expensive and accelerates compressor failure.
The Manual J Heat Load Calculation
The industry-standard method for sizing HVAC systems is called Manual J — a detailed heat load calculation developed by the Air Conditioning Contractors of America (ACCA). Manual J accounts for:
- Square footage and ceiling height
- Insulation levels in walls, ceiling, and floor
- Window area, type, and orientation
- Local design temperature (Georgetown: 101°F)
- Occupancy and internal heat loads
- Infiltration rate (how tight the building envelope is)
The "square footage rule" most contractors use — typically 400–600 sq ft per ton — is a rough approximation that ignores all of these factors. In Georgetown's extreme heat with west-facing windows and cathedral ceilings, that rule can undersize a system by 30%.
Common Georgetown Sizing Mistakes
Builder Undersizing (Most Common)
Volume builders specify systems to minimum code — not to actual heat load. In Georgetown's market, we've measured actual heat loads 15–30% higher than the builder's installed capacity in many Wolf Ranch, Sun City, and Morningstar homes. The homeowner experiences this as "the AC runs all day and never gets the house below 78°F."
Oversizing (Also a Problem)
Oversized systems cool quickly but shut off before completing a full cycle — this is called short-cycling. Short-cycling creates humidity problems (the system doesn't run long enough to remove moisture from the air), uneven temperatures, and accelerated compressor wear from frequent starts. Georgetown's humidity, especially in spring and fall, makes this particularly problematic.
💡 Georgetown Rule: A properly sized system should run 15–20 minute cycles and maintain setpoint on days up to 100°F. If your system runs continuously on a 95°F day without reaching setpoint, it's undersized. If rooms are humid and the system cycles on and off every few minutes, it's oversized.
Georgetown-Specific Sizing Adjustments
For Georgetown homeowners replacing a system, these factors typically increase required capacity above a standard rule-of-thumb calculation:
- West-facing elevation lots (common in Rancho Sienna, Wolf Ranch West): add 0.5 ton
- Cathedral ceilings over 12 feet: add 0.25–0.5 ton per room
- Single-story homes (Sun City): more roof exposure relative to floor area increases load
- Large west/south window areas: each 100 sq ft of west-facing glass adds approximately 0.25 ton of load
- Poor or no attic insulation: common in older Georgetown homes — adds significant load
ProAir Georgetown provides complimentary Manual J calculations for all system replacement consultations. Learn about our AC installation process or call {PHONE_DISPLAY}.