HVAC System Sizing and Efficiency Calculator
Calculate the required HVAC capacity (BTU/hr and tons), heating/cooling loads, and system efficiency metrics including COP, EER, and SEER ratings based on space dimensions, climate, and building characteristics.
Results will appear here.
Formulas Used
Cooling Load (ACCA Manual J Simplified):
Qtotal = (Qwalls + Qceiling + Qfloor + Qwindows,cond + Qsolar + Qoccupants + Qinternal + Qinfiltration) × Climate Factor × 1.10
Qconduction = U × A × ΔT | Qsolar = SHGC × Awin × Isolar | Qinfiltration = 1.1 × CFM × ΔT
CFM = (ACH × Volume) / 60 | 1 Ton = 12,000 BTU/hr
Efficiency Conversions:
EER = SEER × 0.875 | COPcooling = EER / 3.412 | COPheating = HSPF / 3.412
Annual Energy:
kWhcooling = (LoadBTU/hr / (EER × 1000)) × Hours | kWhheating = (LoadBTU/hr × Hours) / (HSPF × 1000)
Assumptions & References
- Cooling and heating loads calculated using ACCA Manual J simplified methodology (ANSI/ACCA Manual J, 8th Edition).
- Average window size assumed at 15 ft² per window (standard residential).
- Occupant sensible heat gain: 250 BTU/hr per person (ASHRAE Standard 62.1).
- Internal gains from lighting and equipment: 3.5 BTU/hr per ft² (residential average per ASHRAE Handbook of Fundamentals).
- Floor heat loss uses 50% of full ΔT to account for ground thermal mass buffering.
- A 10% safety factor is applied to both cooling and heating loads per Manual J recommendations.
- EER ≈ SEER × 0.875 per DOE/AHRI conversion approximation.
- COP = EER or HSPF / 3.412 (1 kW = 3,412 BTU/hr).
- Annual operating hours are climate-zone estimates; actual hours vary by location and thermostat settings.
- Minimum federal SEER standard: 14 SEER (as of 2023, DOE); ENERGY STAR requires ≥ 15 SEER (split systems).
- Minimum federal HSPF standard: 8.2 HSPF (DOE 2023).
- This calculator provides estimates only. A licensed HVAC professional should perform a full Manual J calculation before equipment purchase.