HVAC / BTU Calculator
Calculate the AC/HVAC size needed for a room based on area and climate.
Assumptions used in this calculation
- Rule of thumb: Uses standard BTU-per-square-foot sizing guidelines, not a full Manual J load calculation.
About this calculator
An undersized air conditioner runs constantly without ever quite cooling a room, while an oversized one cycles on and off so fast it can't properly dehumidify, both are common outcomes of guessing at BTU capacity instead of sizing it properly. This calculator starts from a room's floor area, applies a climate-zone multiplier since hotter regions need more cooling capacity per square foot, then adds extra load for the number of occupants (each person generates measurable body heat) and for direct sun exposure, to output a total BTU requirement you can match against AC unit specifications. Entering area, climate and occupancy and getting a single BTU figure back replaces juggling several rule-of-thumb adjustments by hand, adjustments that are easy to skip and end up under- or over-sizing the unit. This is a rule-of-thumb sizing method, not a full Manual J load calculation, so treat the result as a solid starting point and get a professional load calculation for a whole-house system.
Worked example
300 sqft, moderate climate, 2 occupants
Result: 7,500 BTU needed
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