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HVAC sizing: tons, BTUs, and ductwork CFM.

Estimate the cooling-load tonnage and ductwork CFM for a central AC, heat pump, or furnace using a Manual J-style approximation. Real sizing requires a Manual J load calc on your actual home. This calculator gets you in the right neighborhood before you ask three contractors for quotes.

Independent FatBook v3 cost indexVerified permit/source data where availableReviewed by Leonard "Chuck" Thompson
sq ft
Recommended cooling capacity
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Local installed cost

What an installer charges for your scope.

The numbers above are material counts and sizing. Below shows what a contractor typically charges in your city for an installed version of this scope, scaled from FatBook's cost index of BLS wages + Craftsman labor hours + permits + materials.

Pick the cost-index service that matches the scope you're scaling. The default is the trade's headline service.
National Average
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How to use this result
  • Tonnage answers what size cooling unit to buy. CFM answers whether existing ductwork can move that much air.
  • If contractors are recommending more than 0.5 tons above this estimate, ask why. Oversized AC cools the air without removing humidity and short-cycles the compressor.
  • This is a cooling-load estimate. In heating-dominated climates the heating load (for a furnace or heat pump) is usually larger and dictates equipment sizing. Insist on a Manual J for the equipment that runs hardest in your climate.
Cost-index version: 2026.Q2. Read the FatBook methodology, or use the bid and true cost calculators for an installed bid check.
Data Sources Used On This Page
  • Independent FatBook v3 cost index for sizing calculator for Chicago.
  • BLS OEWS wage inputs and FRED PPI material inflation references.
  • Craftsman labor-hour references and contractor overhead benchmarks.
  • Verified permit/source data from PermitCalculator.com and permits_compiled where available.
Cost-index version: 2026.Q2
Updated: May 2026
Sources: BLS, ACCA, Craftsman, FRED
Reviewed by: Leonard "Chuck" Thompson
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Cost index built by David Olson, Founder of TheFatBook · Methodology reviewed by Leonard "Chuck" Thompson, LC Thompson Construction Co., Owner (retired) · 2026.Q1