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Whole-House AC Size Estimate

Get a quick house cooling estimate with editable assumptions. Factors are CalculatorWiser planning scenarios, not coefficients published by ACCA or a calibrated climate model.

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Calculator reference

Whole-House AC Size Estimate

Get a quick house cooling estimate with editable assumptions. Factors are CalculatorWiser planning scenarios, not coefficients published by ACCA or a calibrated climate model.

Formula: Load = area × selected starting rate × climate × insulation × ceiling × sun scenario factors; tons = BTU/h ÷ 12,000.

Preliminary planning only. This heuristic is not Manual J and may miss the actual load by a large amount. Confirm room-by-room sensible and latent loads with Manual J and select equipment with Manual S. Do not automatically round up or add a safety factor.

ACCA Manual J — residential loads

ACCA Manual S — equipment selection

DOE — proper HVAC sizing

Carrier — rough square-foot starting rule

Understanding AC and ductwork estimates

A whole-house square-foot estimate is a starting scenario. Climate, insulation, air leakage, windows, solar exposure, people and duct location can materially change the actual cooling requirement. A large unit can cool the air before removing enough moisture.

Manual J calculates sensible and latent loads. Manual S selects equipment using performance data. Manual D designs the duct system using room airflow, the blower’s pressure capability and the losses of ducts, fittings and components. Velocity-only duct dimensions do not complete that design.

One ton of cooling equals 12,000 BTU per hour. Thermal cooling kW describes heat removed; electrical input kW describes power consumed. Room/window AC estimates use the ENERGY STAR room table separately from the whole-house scenarios.

For heat pumps, cooling results alone cannot select the system: heating output at winter design temperature and backup heat need a separate evaluation. Material calculators estimate quantities; they do not size structural members or establish electrical or plumbing code compliance.

Manual J · Manual S · Manual D