💨 HVAC Calculator PRO
BTU sizing, climate zone adjustments, duct sizing, CFM requirements & cost estimate.
Room Volume — updates as you type
Conditioned space with supply register. Load follows volume plus windows, doors and occupants.
1 Room Dimensions
2 Insulation & Climate
3 Windows, Doors & Occupancy
Kitchen appliances, computers, lighting, etc.
4 Cost & Details
Labour Cost
Results
Cooling / Heating
Airflow & Ducts
Breakdown
Professional HVAC Sizing Guide
Show formulas, climate data & tips ▼
Core Formula
BTU= Floor Area × Ceiling Height × Insulation Factor × Climate Factor × Window Factor × Occupant Factor + Appliance Load
Tonnage = BTU ÷ 12,000
CFM= BTU ÷ (1.08 × ΔT) where ΔT = 20°F typical
Duct Size = √(CFM ÷ (4005 × velocity)) × 12
Insulation Factors
| Level | R-Value | Factor |
|---|---|---|
| Poor | R-11 | 1.3 |
| Average | R-19 | 1.0 |
| Good | R-30 | 0.85 |
| Excellent | R-40+ | 0.75 |
Climate Zone Multipliers
| Zone | Region | Factor |
|---|---|---|
| 1 | Hot (Miami) | 1.4 |
| 2 | Warm (Houston) | 1.25 |
| 3 | Mixed (Atlanta) | 1.1 |
| 4 | Moderate (NYC) | 1.0 |
| 5 | Cool (Chicago) | 0.9 |
| 6 | Cold (Minneapolis) | 0.85 |
| 7 | Very Cold (Fairbanks) | 0.8 |
Common Mistakes
- Oversizing unit — short cycling reduces efficiency and comfort
- Ignoring insulation quality — poor insulation adds 30%+ load
- Forgetting appliance heat — kitchen equipment adds significant BTU
- Not accounting for occupancy — each person adds ~600 BTU sensible heat
- Using wrong climate data — always check ASHRAE zone maps
HVAC — 3D Preview
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Related Calculators
Frequently used together on the same project.
Client & Quote (prints on PDF & Excel)
Adjustments (applies to exports)
Contingency is added as a separate line on the exported cost summary. Waste % is printed as an advisory reminder.
Project notes (prints on PDF & Excel)
Result compare (A/B)
| Item | Pinned | Current | Change |
|---|---|---|---|
Saved rates auto-apply from your Price Library. Advanced details stay in your browser — nothing is uploaded except inside your own PDF/Excel exports.
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📖 How to Use the CVC Calculator
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📐 CVC Formulas & Calculations
CVC formulas and calculations.
⚠️ Common CVC Mistakes
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💡 CVC Pro Tips
Measure twice, cut once
Order 10% extra for waste
❓ CVC Calculator FAQ
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✅Method, Sources & Review
Maintained by theBuildingCalc methods desk· Last reviewedSeptember 23, 2026. This calculator implements the standards and references below; every figure can be rechecked against the formulas and worked example on this page.
Results are estimates, not engineering advice. Verify against local codes and licensed professionals for structural, electrical, and gas work. See ourTerms. Spotted an error? Report it— corrections ship with the next review.