HVAC Load Calculator
PopularManual J-compliant HVAC load calculations for residential and commercial.
HVAC Load Calculator
Enter your figures below
Size heating and cooling equipment correctly with a simplified Manual J load estimate. Oversized systems short-cycle, waste energy, and leave rooms uncomfortable — this gets you in the right ballpark before you spec equipment.
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Enter the conditioned square footage of the space you're sizing.
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Pick the climate zone and number of occupants so the estimate reflects real heat gain.
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Hit Calculate to get an estimated BTU load and a suggested system size.
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Use AI deep-dive for room-by-room notes, then confirm with a full Manual J before purchasing.
- HVAC contractors giving a fast, defensible first-pass size on a sales call.
- Homeowners sanity-checking a contractor's equipment recommendation before signing.
- Builders and remodelers budgeting equipment for a new layout or addition.
Is this a full Manual J calculation?+
No — it's a simplified estimate, typically within 10–15% of a full Manual J for standard homes. Use it to ballpark and sanity-check, then commission a full load calc for permits and final equipment selection.
What inputs affect the result most?+
Square footage and climate zone dominate, with occupancy and orientation as secondary factors. A full Manual J also weighs insulation R-values, infiltration, and duct leakage.
Can I use this for commercial spaces?+
It's tuned for residential and light-commercial. Large or complex commercial loads should use Manual N / dedicated software.