Austin Climate Load Calculator
Estimates residential heating and cooling loads for Austin, TX using the Manual J simplified method with Austin-specific climate design conditions (ASHRAE 99%/1% design temperatures).
Building Envelope
Construction & Infiltration
Formulas Used
Conduction: Q = U × A × ΔT (BTU/hr)
Solar gain: Qsolar = SHGC × Awin × SHGF × IAC
Infiltration (sensible): Q = 1.1 × CFM × ΔT
Infiltration (latent): Q = 0.68 × CFM × Δgrains
CFM: ACH × Volume / 60 | ACH = factor × (ΔT/10)0.4
Slab edge (heating): Q = F2 × Perimeter × ΔT (F2 = 0.73 BTU/hr·ft·°F)
Duct losses: 15% cooling / 20% heating (attic ducts, Austin typical)
Cooling tons: Total BTU/hr ÷ 12,000
Assumptions & References
- Austin design conditions (ASHRAE 2021): Cooling 101°F DB / 76°F WB (99th percentile); Heating 28°F DB (99th percentile)
- Slab edge factor F2 = 0.73 BTU/hr·ft·°F (ASHRAE, uninsulated slab, Austin soil)
- References: ASHRAE Handbook of Fundamentals 2021; ACCA Manual J 8th Ed.; ACCA Manual S; Austin Energy Green Building Guidelines; Texas IECC 2021