Free Tool
Free HVAC load calculator
Estimate the cooling tons a home needs from its square footage and climate. A quick sanity check on equipment size. Free, no signup.
Conditioned living area
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A gut check on the tonnage
Before you quote a system, it helps to know roughly what the house calls for. This gives you a ballpark from the square footage and your climate, so you can sniff out a unit that is badly under or oversized.
It multiplies the conditioned area by a BTU-per-square-foot factor for your climate, adds a little for the people inside, and converts to tons at 12,000 BTU per ton. Warmer climates carry a higher factor, since the same house works the system harder in the deep south than up north.
Bigger is not better with air conditioning. An oversized unit cools the air fast, shuts off, and never runs long enough to pull the humidity out, so the house feels clammy and the compressor wears from short-cycling. The rule of thumb tends to oversize, which is exactly the trap.
That is why this is a check, not a design. A real Manual J load calculation accounts for insulation, windows, orientation, air leakage, and the ductwork, and a licensed HVAC pro should size the actual unit off it.
HVAC Load Calculator questions
What size AC do I need?
Roughly the square footage times a climate factor, converted to tons. This calculator estimates it, but a Manual J sizes the real unit.
How many square feet per ton?
Often around 400 to 600 depending on climate and the house, which is what the per-foot factor works out to. It is a starting point, not a rule.
Why not just go bigger?
An oversized unit short-cycles and leaves the house humid. Right-sizing from a Manual J is what keeps it comfortable and efficient.
Is this really free?
Yes. No email, no signup, and nothing you type leaves your browser.
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Disclaimer: These free tools and templates are provided for general information and estimating purposes only. All results — including quantities, material and cost estimates, load, sizing, and span figures, scores, and any guidance or warnings — are rough approximations that may not fit your specific project, site conditions, local building codes, or current prices. They are not engineering, architectural, structural, legal, financial, or other professional advice, and are not a substitute for a licensed engineer, architect, contractor, or other qualified professional. Always confirm quantities, sizing, and structural, electrical, mechanical, and code requirements with a licensed professional and your local authority having jurisdiction before purchasing materials or performing any work. Werx makes no warranty as to accuracy and accepts no liability for any decision made using these tools. Use at your own risk. See our Terms of Service.