Free Manual J Load Calculator: Size Your Mini Split by Zone Air
Our free Manual J–style load calculator estimates the heating and cooling load (in BTU) for any room based on square footage, climate, insulation, and sun exposure — then recommends the right mini split size. No signup, no cost, results in minutes.
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What a Manual J Load Calculation Does
A Manual J load calculation is the industry method for sizing HVAC equipment to a space. Instead of guessing, it weighs square footage, ceiling height, insulation, windows, sun exposure, and climate to estimate how many BTU you actually need. Oversizing wastes money and short-cycles the system; undersizing leaves rooms uncomfortable. Our calculator runs a fast, Manual J–style estimate so you buy the right size the first time.
As a starting point, plan on roughly 20 BTU per square foot: about 9,000 BTU for 200–350 sq ft, 12,000 BTU for 350–550 sq ft, and 18,000 BTU for 600–800 sq ft. The calculator adjusts those numbers for your specific room.
Run Your Free Load Calculation
Enter your room details and get a recommended BTU size in under a minute — free and no signup.
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