HVAC Load Calculator
Calculate the exact BTU/hr needed for cooling and heating. Get AC tonnage recommendations and avoid costly oversizing or undersizing mistakes.
Room Dimensions
Room Factors
Cooling Load
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BTU/hr
Heating Load
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BTU/hr
AC Tonnage
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tons
Recommended Size
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Est. Annual Cost
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Suggested Unit Sizes
AC Unit Size Reference Guide
| Tonnage | BTU/hr | Sq Ft Range | Typical Use |
|---|---|---|---|
| 1.0 ton | 12,000 | 300–450 sq ft | Studio, small bedroom |
| 1.5 ton | 18,000 | 600–900 sq ft | Large bedroom, small apt |
| 2.0 ton | 24,000 | 900–1,200 sq ft | Small home, large apt |
| 2.5 ton | 30,000 | 1,200–1,500 sq ft | Medium home |
| 3.0 ton | 36,000 | 1,500–1,800 sq ft | Medium-large home |
| 3.5 ton | 42,000 | 1,800–2,100 sq ft | Large home |
| 4.0 ton | 48,000 | 2,100–2,400 sq ft | Large home, open plan |
| 5.0 ton | 60,000 | 2,400–3,000 sq ft | Large/custom home |
Saved Estimates
Total Cooling
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BTU/hr
Total Heating
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BTU/hr
Total Tonnage
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tons
Est. Annual Cost
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How HVAC Sizing Works
Manual J Simplified
This calculator uses a simplified version of ACCA Manual J — the industry standard for residential load calculations. It accounts for square footage, ceiling height, climate, insulation, sun exposure, windows, and occupants to estimate your true BTU needs.
Why Oversizing Hurts
An oversized AC unit short-cycles — it cools the room too fast, shuts off, then restarts. This creates humidity problems, temperature swings, higher wear on the compressor, and wasted energy. Bigger is NOT better in HVAC. Right-sizing saves money and improves comfort.
Understanding SEER Ratings
SEER (Seasonal Energy Efficiency Ratio) measures how efficiently an AC unit operates. SEER 14 is the federal minimum; SEER 16–20 are efficient; SEER 21+ are premium. Higher SEER = lower electricity bills, but higher upfront cost. Most homeowners break even upgrading to SEER 16 within 3–5 years.
Key Sizing Notes
- Each person generates approximately 600 BTU/hr of heat — occupancy matters
- Kitchens add ~4,000 BTU due to cooking heat gain — always size up for kitchen zones
- Ceiling heights above 8 ft increase the volume of air to condition — use the ceiling height input
- For whole-home systems, use Multi-Room mode and sum all zones
- This calculator is for planning only — always have a licensed HVAC contractor perform a full Manual J before purchase
- Energy cost estimate assumes 14¢/kWh average, SEER 15 unit, running ~1,500 hours/year for cooling
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