Sizing Calculator Disclaimer

Last Updated: June 15, 2026

ASHRAE / ACCA Manual J-style worksheet for cooling load (heat gain) only. Practical estimator for AC sizing. Window solar gain scales with the selected ASHRAE climate zone (latitude band). All fields optional. Progress section-by-section (mobile friendly).

Calculate requires at minimum: positive wall areas for North/South/East/West + ceiling area + floor area.

1. Purpose

The Residential Heat Gain Calculator is intended as a simple, mobile-friendly worksheet for HVAC technicians and homeowners who want a quick cooling-load estimate. Residential systems use a limited set of standard tonnages; experienced techs often size from field judgment — this tool supports that practice with transparent math, not replace it.

2. What This Tool Provides

• Sensible cooling load estimates using ASHRAE-inspired methods
• Orientation-based window solar gain scaled by ASHRAE climate zone
• Wall, ceiling, floor, door, infiltration, and internal gain components
• A practical tonnage suggestion for field reference

3. What This Tool Does Not Provide

This is not engineer-grade load software. It does not include:

• Full ACCA Manual J room-by-room calculations
• Latent (humidity) cooling load analysis
• City- or weather-station-specific design data
• Window shading, overhangs, or interior shade modeling
• Detailed duct-loss and leakage calculations
• Ventilation load per ASHRAE 62.2
• Equipment selection per Manual S

Full Manual J is typically used when a documented engineering calculation is required — new construction, permits, unusual buildings, or formal equipment selection. Most residential replacement work relies on field experience and standard equipment sizes.

4. How to Use Results

• Use results as a sanity check, not the sole basis for equipment selection.
• Cross-check airflow with the in-app Air Flow tool when needed.
• Add approximately 10–15% for duct gains when ducts run in unconditioned space.
• Always verify with manufacturer data, local codes, and your own gauges.

5. Limitation of Liability

Peter's HVAC Advisory provides this tool free of charge, as is. We assume no liability for incorrect calculations, oversized or undersized equipment, property damage, comfort issues, or any losses resulting from use of this estimator.

Final equipment selection and installation must be performed by a qualified HVAC technician in accordance with local codes and manufacturer requirements.

6. Accuracy

We aim to keep the calculator accurate but simple. Methods are simplified from industry practice and ASHRAE principles. All input fields are optional except the minimum required for calculation; incomplete data produces incomplete estimates.