CFM for 3-ton AC?
About 1,200 CFM using the 400 CFM per ton rule of thumb.
Room cooling BTU/hr ≈ sq ft × climate factor × insulation factor × (ceiling height ÷ 8). One ton of cooling = 12,000 BTU/hr.
Use the calculator form above with your room size, system capacity, or appliance usage. Results update instantly in your browser — no data is sent to a server.
Concise answers for common searches — definitions, steps, and comparisons.
About 1,200 CFM using the 400 CFM per ton rule of thumb.
12,000 BTU/hr of cooling capacity equals one ton of refrigeration.
Room cooling BTU/hr ≈ sq ft × climate factor × insulation factor × (ceiling height ÷ 8). One ton of cooling = 12,000 BTU/hr.
Formula
See calculator inputs and results panel for step-by-step math.Select imperial/metric, rectangle vs area, tons vs BTU, or usage presets as shown.
Type room dimensions, system tonnage, CFM, appliance watts, or electric rate.
Pick climate zone 1–5 and insulation quality for load-based calculators.
Use BTU/hr, tons, CFM, duct diameter, or seasonal cost in the results panel.
Copy results or share a link with your HVAC contractor or energy auditor.
Use Duct CFM, Duct Size, or Energy Cost calculators for a complete HVAC plan.
Input
20×15 ft · 8 ft ceiling · zone 3Output
≈ 7,500 BTU/hr cooling300 sq ft × 25 BTU/sq ft × average insulation × 1.0 height factor.
Input
2.5 tonsOutput
1,000 CFM2.5 × 400 CFM/ton = 1,000 CFM supply airflow rule of thumb.
Common real-world scenarios where this tool saves time.
12×15 ft room, zone 3, average insulation → ~9,000–11,000 BTU/hr cooling load.
2,000 sq ft home, zone 4 → ~3.5–4 tons cooling with average insulation.
3-ton system → 1,200 CFM target → 14" round trunk at 700 FPM velocity.
900 W unit, 8 hr/day, 90 days at $0.16/kWh → seasonal cost estimate for budgeting.
Step-by-step chains that connect related tools for common tasks.
From room BTU to duct airflow and diameter.
Compare portable appliance electricity spending.
| Zone | Climate | BTU/sq ft (cooling) |
|---|---|---|
| 1 | Very hot | 30 |
| 3 | Mixed | 25 |
| 5 | Very cold | 20 |
Rule-of-thumb sizing is a starting point — ACCA Manual J is the industry standard.
Undersized ducts reduce efficiency and comfort even when tonnage is correct.
Include climate zone, insulation, ceiling height, and sun exposure — or request Manual J.
Check heating BTU/hr and balance point, not just cooling tons.
Compressors cycle — actual kWh may be lower than watts × hours suggests.
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Roughly 20–30 BTU/sq ft depending on climate zone — hotter regions need more cooling BTU per square foot.
Taller ceilings and poor insulation increase load — this calculator applies a height factor and insulation multiplier to base BTU/sq ft.
One ton of air conditioning equals 12,000 BTU/hr of cooling capacity.
Yes for ductless or window units; whole-home systems also need whole-house load calculations beyond a single room.
South- and west-facing rooms with large windows often need 10–15% more BTU than the base estimate.
No — it is a simplified homeowner estimator. Licensed HVAC contractors use Manual J for permit-grade designs.
Room dimensions and climate inputs for the BTU Room Calculator stay on your device — EverydayTools does not upload HVAC sizing data.
Estimates only — not professional HVAC or energy audit advice. Verify with a licensed contractor before purchasing equipment.
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Reviewed on 2026-06-28.
Same workflow or intent — pick the next step without leaving the site.
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Standard ceiling is 8 ft