HVAC Load Calculator — Simplified BTU Estimate

How to use

1. Enter the space: length × width or direct area, and the ceiling height.
2. Pick the climate zone that matches your summer, not your winter.
3. Set insulation, sun, occupants and windows honestly — padding inputs pads the tonnage.
4. Read BTU/h, tonnage and the nearest standard unit class to buy.

About this tool

A real Manual J takes plans, blower-door data and software; this HVAC load calculator is the honest shortcut installers sketch on the back of an invoice, and it is labeled a simplified estimate for a reason. You pick a climate zone — hot Gulf Coast to very-cold upper Midwest, each with its own BTU-per-square-foot factor — then adjust for what actually moves the load: ceiling height, insulation quality, sun exposure, occupants beyond two, window count and glazing type, and whether a kitchen shares the space. The output is a cooling load in BTU per hour, tonnage at 12,000 BTU per ton, and the nearest standard equipment class to shop for, from window unit to whole-home system. Use it to sanity-check contractor quotes and rule out wildly oversized units, not to size a system for permit — oversized equipment short-cycles, dehumidifies poorly and wears out early. Every number is computed in your browser and never uploaded.

FAQ

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