HVAC Equipment Sizing Calculator — Manual J Load Estimate
Estimates residential heating and cooling loads using the Manual J simplified methodology to properly size HVAC equipment. Enter your home's characteristics to calculate BTU/hr requirements.
Climate & Location
Building Envelope
Windows & Doors
Infiltration & Internal Gains
Formulas Used (Manual J Simplified)
Heating Load (each component):
Qheat = U × A × ΔTwinter
where U = 1/R (BTU/hr·ft²·°F), A = area (ft²), ΔT = Tindoor − Toutdoor design
Infiltration Heating:
Qinf,heat = 1.1 × CFM × ΔT
CFM = ACH × Volume(ft³) / 60
Cooling Sensible Load:
Qcool,sens = Σ(U × A × ΔTsummer) + Qsolar + Qinternal + Qinf,sens
Qsolar = SHGC × Awindow × 250 BTU/hr·ft² × Orientation Factor
Cooling Latent Load:
Qlat,inf = 0.68 × CFM × ΔW (gr/lb)
Qlat,occ = Occupants × 200 BTU/hr
Total Cooling: Qtotal = Qsensible + Qlatent
Tons: Tons = Qtotal / 12,000 BTU/hr per ton
Duct Loss Factor applied to all loads (1.0–1.3×)
Assumptions & References
- Based on ACCA Manual J 8th Edition simplified residential load calculation methodology