Manual J calculator: free load estimate.
Free Manual J style estimate: heating and cooling load in Btu/h and AC or heat pump size in tons from floor area, climate zone and insulation. Plus the real Manual J, S and D for $100.
What this calculator does
It multiplies your floor area by typical heating and cooling loads per square foot for your IECC climate zone and adjusts them for insulation level, window area and ceiling height. The result is a range in Btu per hour and an approximate equipment size in tons. Use it to check a quote or to plan a budget.
What it does not do
It is not a Manual J. A real Manual J calculates every room from the plans: wall, ceiling and floor assemblies, every window with its U-factor and solar heat gain coefficient, orientation, air leakage, duct location and the local design temperatures. Building departments require that calculation for the permit, not an estimate.
Why the result is a range
Two houses with the same floor area in the same town can differ by 30% or more in load. West-facing glass, a leaky attic or ducts in a vented attic push the cooling load up; a tight, well-insulated house with good windows brings it down. That is why sizing by square feet per ton usually oversizes.
From estimate to permit
When you need the number for the permit, send the plans: we prepare Manual J, Manual S and Manual D together for $100 per house and deliver a permit-ready PDF.
Estimate only. Last reviewed November 2026.
Manual J, S & D for $100.
Permit-ready load calculation, equipment selection and duct design from your plans, delivered as one PDF.
- J + S + D for $100
- Permit-ready PDF
- 2–3 business days
- No subscription
Free quote confirmation, no account needed. You pay per house, no subscription.
Manual J Calculator: answered.
Is a Manual J calculator accurate enough for a permit?
No. Online calculators give a rough range. Codes (IRC M1401.3, IECC R403.7) require equipment sizing with ACCA Manual S based on a Manual J load calculation from the actual building.
How many square feet per ton is normal?
Rules of thumb say 400 to 600 square feet per ton, but a Manual J for a new, well-insulated home often lands at 700 to 1,000 or more. That gap is why rules of thumb oversize.
What size heat pump do I need?
Size it to the Manual J heating and cooling loads at your design temperatures and check it with manufacturer data in Manual S. The calculator above gives a first range.
How much does a Manual J cost?
$100 per house for Manual J, Manual S and Manual D together. No subscription and no minimum order.
How fast do I get the report?
Usually 2–3 business days after we receive complete plans and specs.
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