AC Size Estimator
Estimates a home's required air conditioner size in tons based on basic home characteristics.
What this is for
Estimates a rough central AC capacity (in tons) from square footage plus simple adjustments for insulation, sun exposure, windows, and occupants. It does not perform a full HVAC load calculation and does not account for many building and climate variables beyond the provided inputs.
Inputs needed
- What is the ZIP code? (ZIP code; text; optional). Collected on the page but not used in the sizing calculation shown in the JavaScript.
- How many square feet is the home? (sq ft; number). Used to compute the base BTU/hr load.
- What is the home's insulation quality? (category; one of: Poor, Average, Good, Excellent). Applies a multiplier to the base BTU/hr.
- What is the home's sun exposure level? (category; one of: Low, Moderate, High). Applies a multiplier to the BTU/hr after insulation adjustment.
- How many windows are in the home? (windows; number). Adds a fixed BTU/hr amount per window.
- How many residents live in the home? (people; number). Adds a fixed BTU/hr amount per resident.
How it's calculated
Compute a base cooling load in BTU/hr as square footage × 20.
Adjust this BTU/hr by multiplying by an insulation multiplier: Poor 1.2, Average 1.0, Good 0.8, Excellent 0.6. Then multiply by a sun exposure multiplier: Low 0.9, Moderate 1.0, High 1.1.
Add window and occupancy loads: add (number of windows × 500 BTU/hr) and add (number of residents × 400 BTU/hr). Convert BTU/hr to tons using 12,000 BTU/hr per ton, then round up to the nearest 0.25 ton using: tons = ceil((BTU/hr ÷ 12,000) × 4) ÷ 4.
Result
Present the estimated AC size in tons (rounded up to the nearest 0.25 ton) and include the underlying BTU/hr basis in parentheses (e.g., “Based on X BTU/hr”).
Limitations
This is a simplified sizing estimate based on a fixed BTU-per-square-foot rule plus a few multipliers and adders; it does not incorporate many factors that affect HVAC load (e.g., ceiling height, duct losses, airtightness, shading details, orientation, or equipment performance). The ZIP code field is not used in the calculation logic shown on the page.
When to consult a professional
A professional HVAC load calculation is recommended when selecting equipment for purchase/installation, when comfort or humidity problems exist, or when the home has atypical features (large glass areas, additions, vaulted ceilings, or uneven temperatures).
Source
Original tool: <https://greenleafair.com/tools/ac-size-estimator>