BTU / HVAC Sizing Calculator

Answer a few simple questions about your home and we'll estimate the right AC size for Central Texas. This tool accounts for our hot-humid climate, attic ductwork, home age, and more — but a professional Manual J calculation is recommended before making a final decision.

Helps estimate insulation & air sealing quality
Attic temps can reach 150°F, affecting system efficiency

Understanding BTU and HVAC Sizing

BTU stands for British Thermal Unit — it measures the amount of heat an air conditioning system can remove from your home per hour. In Central Texas (ASHRAE Climate Zone 2A), where summer design temperatures reach 99–101°F and cooling season lasts 8–9 months, getting the right size system is critical for both comfort and energy efficiency.

Why Correct Sizing Matters in Texas

An oversized system is the most common problem in Texas homes. Studies show the average Texas home is oversized by 35–50%. An oversized AC short cycles — turning on and off every few minutes — which wastes energy, creates uneven temperatures, and critically fails to dehumidify. In Central Texas humidity, this means your home feels cold and clammy even at the right temperature. An undersized system will run constantly on the hottest days without reaching your set temperature and wear out faster.

What Our Calculator Considers

  • Home age: Older homes (pre-1980) typically have poor insulation and air sealing, requiring up to 30% more cooling capacity
  • Attic ductwork: Most Texas homes run ducts through unconditioned attics that reach 130–150°F in summer, adding roughly 20% to system needs
  • Humidity (latent load): Central Texas humidity means 25–30% of your cooling load goes to moisture removal, not just temperature
  • Window type: Single-pane windows let in dramatically more heat than low-E double-pane
  • Occupants: Each person adds approximately 600 BTU/hr of heat

Manual J: The Gold Standard

This calculator provides a useful estimate based on industry guidelines, but the only code-compliant method for HVAC sizing is an ACCA Manual J load calculation — which Texas building code requires for new installations. Manual J considers 30+ factors including exact insulation R-values, window orientation, air infiltration rates, and duct conditions that can only be measured on-site. Our estimates are typically within ±15–20% of a professional calculation.

Contact Texas Temp Masters for a free in-home assessment and professional Manual J calculation before making your final purchase decision.

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