RTU
Sizing Helper (Rule-of-Thumb)

How to Estimate RTU Sizing for Commercial Buildings

Rooftop unit sizing is typically measured in tons of cooling capacity. A rough rule of thumb is 400-600 square feet per ton depending on building type, climate, and ceiling height — but proper sizing requires a Manual J or equivalent load calculation.

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Rule-of-Thumb Sizing Guidelines

Standard offices typically need 1 ton per 400-500 sq ft. Open floor plans are more efficient; lots of private offices with glass reduce efficiency.

Retail spaces vary widely. A small boutique runs 400-500 sq ft/ton. A big box store with high ceilings might push 600+ sq ft/ton.

Restaurants have high heat loads from cooking equipment. Expect 200-300 sq ft/ton — sometimes even less for heavy kitchen areas.

Medical facilities often require more capacity due to fresh air requirements and sensitive environments. Budget 300-400 sq ft/ton.

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What This Tool Does (and Doesn't Do)

This is a sanity-check tool, not a design tool. Use it to catch obvious sizing errors — like a 5-ton unit proposed for a 15,000 sq ft building.

For actual equipment selection, you need a full load calculation that accounts for windows, insulation, occupancy, kitchen heat, fresh air requirements, and more.

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Who Uses This Tool

HVAC contractors use it to quickly estimate replacement tonnage before a site visit. Facility managers use it to validate contractor proposals.

Enter your building details for a rough tonnage range and recommended next steps.