Enter floor area and ceiling height, pick climate zone, insulation, and sun exposure BTU loads, tonnage, and CFM update live.
Climate zone
Insulation quality
+0%
Recommended AC size
4.5
TONS
Bill of materials+0% waste
Cooling load
Zone 3–4 · Moderate · 27.5 BTU/sq ft
Net 49,500 BTU/hr base · Waste —
AC condenser size
Rounded up to nearest ½ ton
Net 50,300 BTU/hr · Waste —
Heating load
35 BTU/sq ft · cooling priority climate
Net 63,000 BTU/hr · Waste —
Airflow requirement
≈400 CFM per ton
Net 4.5 tons · Waste —
Cost projection
Saved on this device · No account · No cloud
Total · $16,470.00
4.5 tons 50,300 BTU/hr
Base cooling = floor area × zone factor × (ceiling height ÷ 8): 32.5 BTU/sq ft for hot/humid zones 1–2, 27.5 for moderate zones 3–4, 22 for cold zones 5–7.
Enter floor area and ceiling height, pick climate zone, insulation, and sun exposure BTU loads, tonnage, and CFM update live.
Adjustments: poor insulation +20%, high-efficiency −15%; heavy sun +10%, shaded −10%; plus 400 BTU per occupant above 2.
Tonnage rounds UP to the nearest half ton (12,000 BTU = 1 ton) and airflow runs ≈400 CFM per ton. These are bid-scoping rules of thumb confirm with an ACCA Manual J.
BTU = sq ft × zone factor → ½-ton rounds
Cooling rule of thumb: 32.5 BTU/sq ft in hot/humid zones 1–2, 27.5 in moderate zones 3–4, and 22 in cold zones 5–7, adjusted for ceiling height, insulation, and sun exposure. The tool applies your climate zone plus occupancy and shading adjustments automatically.
Divide total cooling BTU by 12,000 (1 ton) and round UP to the nearest half ton — an 1,800 sq ft home in a moderate zone lands near 4.5 tons. The tool sizes tonnage and estimates ≈ 400 CFM per ton for duct planning.
About 400 CFM per ton — a 3-ton system needs roughly 1,200 CFM of airflow. Undersized ductwork is the most common cause of poor cooling.
In a moderate zone (27.5 BTU/sq ft): 1,800 × 27.5 = 49,500 BTU/hr base; with average insulation and 4 occupants the tool lands around 50,300 BTU/hr → 4.5 tons. Confirm final equipment selection with an ACCA Manual J.
Poor insulation adds ~20% to the load; a high-efficiency envelope cuts ~15%. Heavy sun exposure adds ~10%, heavy shade subtracts ~10%. These are bid-scoping rules of thumb — confirm with a Manual J before ordering equipment.
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