HVAC BTU & Tonnage Calculator
Find the correct AC unit size for your home. Based on Manual J load calculation principles used by HVAC professionals.
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How to Size an HVAC System
Choosing the wrong size HVAC system is one of the most costly mistakes homeowners make. An undersized unit runs constantly without reaching the set temperature. An oversized unit short-cycles — turning on and off too frequently — which causes premature wear, poor dehumidification, and higher energy bills.
The industry standard for HVAC sizing is the Manual J load calculation, developed by the Air Conditioning Contractors of America (ACCA). This calculator uses the most impactful factors to give you a reliable estimate.
What is BTU and Tonnage?
BTU stands for British Thermal Unit — the amount of heat needed to raise one pound of water by one degree Fahrenheit. Tonnage is the widely-used measurement: 1 ton of cooling = 12,000 BTU/hour.
- 1.5 ton = 18,000 BTU/hour
- 2 ton = 24,000 BTU/hour
- 2.5 ton = 30,000 BTU/hour
- 3 ton = 36,000 BTU/hour
- 4 ton = 48,000 BTU/hour
- 5 ton = 60,000 BTU/hour
Rule of Thumb
The rough industry rule is 20 BTU per square foot in a temperate climate with average insulation. A 1,500 sq ft home needs roughly 30,000 BTU (2.5-ton system). This must be adjusted significantly for climate, insulation, ceiling height, and sun exposure.
Always Get a Professional Manual J
For a definitive answer, hire a licensed HVAC contractor to perform a full Manual J load calculation before purchasing equipment. A proper Manual J takes 2–4 hours and accounts for your home's exact orientation, window square footage, ductwork design, and local climate data.
What size AC unit do I need for a 1,500 sq ft house?
For a 1,500 sq ft home with average insulation in a warm climate, you typically need a 2.5-ton (30,000 BTU) system. This can vary from 2 tons in a well-insulated home in a mild climate to 3 tons in a poorly insulated home in a hot climate.
What size AC unit do I need for 2,000 square feet?
A 2,000 sq ft home with average insulation in a warm climate typically needs a 3-ton (36,000 BTU) system. Adjust up to 3.5 or 4 tons for hot climates or poor insulation.
Is it better to oversize or undersize an AC unit?
Neither — both cause problems. Oversized units short-cycle (run in short bursts), creating humidity problems and uneven temperatures. Undersized units run constantly and wear out faster. The right size runs in longer, efficient cycles that properly dehumidify the space.
Do I need the same size for heating as cooling?
For heat pumps, cooling load is typically the dominant factor in warm and mixed climates. In very cold climates, a heat pump may need a supplemental electric or gas furnace to handle extreme temperatures.