A proper HVAC load calculation (Manual J) considers dozens of factors including wall construction, roof type, window orientation, duct losses, infiltration rates, and internal heat gains. This calculator provides a simplified estimate based on the most impactful variables — useful for initial budgeting and right-sizing.
Why Right-Sizing Matters
Oversized systems: Short-cycle (turn on/off frequently), waste energy, fail to dehumidify, cause hot/cold spots, and wear out faster
Undersized systems: Run constantly, can't reach setpoint on extreme days, higher energy bills
Zones 1–2 (Hot): Cooling-dominant. Size primarily for cooling load. Heating is minimal.
Zones 3–4 (Moderate): Balanced heating and cooling needs. Most common residential scenario.
Zones 5–7 (Cold): Heating-dominant. Heating load typically exceeds cooling load significantly. Consider heat pumps with auxiliary heat.
SEER Ratings & Efficiency
SEER (Seasonal Energy Efficiency Ratio) measures cooling efficiency. As of January 2023, the minimum SEER rating is 14 in northern states and 15 in southern states. Higher SEER ratings (16–25+) cost more upfront but save on operating costs. A 16 SEER unit uses about 12% less energy than a 14 SEER unit.
Standard Equipment Sizes
1.5 ton (18,000 BTU): 600–900 sq ft
2 ton (24,000 BTU): 901–1,200 sq ft
2.5 ton (30,000 BTU): 1,201–1,500 sq ft
3 ton (36,000 BTU): 1,501–1,800 sq ft
3.5 ton (42,000 BTU): 1,801–2,100 sq ft
4 ton (48,000 BTU): 2,101–2,400 sq ft
5 ton (60,000 BTU): 2,401–3,000 sq ft
HVAC load calculated?
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