BTU Load for 3,500 sq ft — Climate Zone 1 (Very Hot-Humid)
How This Was Calculated
Simplified Manual J methodology. Cooling: 3500 sqft × 35 BTU/sqft (zone 1) × 1.0 (average insulation) × 1.0 (8 ft ceiling) × 1.0 (15% windows).
- sqft
- Conditioned area: 3,500 sq ft
- zone_multiplier
- Zone 1 cooling factor: 35 BTU/sqft
- insulation_factor
- Insulation adjustment: 1.0 (average)
- Q_cool
- Cooling load: 122,500 BTU/hr
Important Considerations
This estimate uses simplified multipliers based on ACCA Manual J methodology. For equipment selection, a full Manual J room-by-room calculation is strongly recommended and required by code (ACCA Standard 5, IRC Section M1401) in many jurisdictions. Manual J accounts for: actual window area, orientation, and SHGC; wall and ceiling R-values; infiltration; duct location; internal gains; and local design temperatures. Automated Manual J software (WrightSoft, RHVAC, CoolCalc) produces code-compliant reports for a few hundred dollars — a worthwhile investment before a $5,000–$15,000 equipment purchase.
Zone 1 (Miami, Key West, Honolulu) has minimal heating loads but extreme cooling and dehumidification demands year-round. Latent (moisture) load often exceeds sensible (temperature) load — equipment must be sized for dehumidification, not just cooling BTU. High-efficiency dehumidification mode, variable-speed compressors, and enhanced drainage are critical. Heating system sizing is typically not a limiting factor.
Total cooling load = sensible load (temperature) + latent load (humidity removal). In humid climates (zones 1–3 humid, coastal zones 4), latent load can be 30–50% of total cooling load. Standard SEER ratings are measured at fixed conditions that may not reflect latent performance. For homes with humidity complaints, look for equipment with enhanced dehumidification modes, variable-speed compressors (better part-load latent removal), or dedicated whole-house dehumidifiers. Target indoor relative humidity of 40–50% for comfort and mold prevention.
Heating and cooling load estimates use a simplified methodology based on ACCA Manual J (Residential Load Calculation, 8th Edition) with climate zone multipliers from IECC 2021. For accurate sizing, a full Manual J calculation using room-by-room analysis is recommended per ACCA Standard 5 (HVAC Quality Installation Specification).