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Free HVAC Load Calculator

Get accurate heating and cooling BTU calculations in 60 seconds. Upload your blueprint—our AI delivers permit-ready results.

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No credit card required • Results in 60 seconds

Why "Rules of Thumb" Lead to Wrong-Sized Equipment

"One ton per 500 square feet" ignores everything that actually matters. Here's why simple calculators get it wrong.

Same Square Footage. Completely Different Loads.

1960s Ranch

2,000 sq ft

  • • Single-pane windows
  • • R-11 wall insulation
  • • Leaky envelope (12 ACH50)
  • • Uninsulated crawlspace

Heating: 85,000 BTU

Cooling: 48,000 BTU (4 ton)

2020 New Build

2,000 sq ft

  • • Triple-pane windows
  • • R-21 + R-5 walls
  • • Tight envelope (2 ACH50)
  • • Insulated slab

Heating: 35,000 BTU

Cooling: 24,000 BTU (2 ton)

Same size. 2.5x different load. A simple calculator would recommend identical equipment for both.

Simple BTU Calculators

  • Square footage × magic number
  • Ignore insulation R-values
  • Ignore window specs and orientation
  • Ignore air leakage and duct losses
  • Won't pass permit inspection

AutoHVAC Load Calculator

  • AI reads your actual blueprint
  • Extracts R-values, U-factors, SHGC
  • Calculates infiltration and duct losses
  • Full ACCA Manual J methodology
  • Permit-ready PDF in 60 seconds

What Actually Determines Your HVAC Load

Real load calculation considers 30+ factors. Here are the big ones.

Windows & Orientation

Window area, type, and direction can swing cooling loads by 30%+. South and west windows add massive solar gains.

Insulation & Envelope

Wall R-values, ceiling insulation, and air sealing determine how fast heat escapes. Modern homes need half the capacity.

Infiltration & Ducts

Air leakage and duct location can account for 30-40% of total load. Leaky ducts in hot attics are equipment killers.

AutoHVAC analyzes all of this from your blueprint—automatically

Get Accurate Load Calculation Free

How Our HVAC Load Calculator Works

Upload. Analyze. Download. That's it.

Step 1

Upload Blueprint

Any blueprint PDF works. Floor plans, elevations, energy specs—our AI handles them all.

Step 2

AI Calculates Loads

AI extracts building specs and runs full Manual J calculations. Heating, cooling, room-by-room.

Step 3

Get Your Report

Download a complete, permit-ready load calculation with equipment recommendations.

What's Included in Your Load Calculation

Heating Load

Precise BTU/hr heating requirements based on design day temperatures for your climate zone.

Cooling Load

Sensible and latent cooling loads with proper dehumidification sizing.

Equipment Sizing

Furnace capacity and AC tonnage recommendations based on calculated loads.

Permit-Ready PDF

Professional documentation that meets building department requirements.

Get Accurate HVAC Loads in 60 Seconds

Stop using rules of thumb. Stop oversizing equipment. Upload your blueprint and get real Manual J load calculations—first one's free.

Upload Blueprint & Calculate Free

No credit card required • No software to install • Results in 60 seconds