Updated for 2026 DOE Standards

Stop Guessing.
Start Sizing.

The professionally accurate Manual J load calculator for homeowners and DIYers. Avoid oversizing, save money, and get your permit approved.

ACCA Methods
SEER2 Ready
Free Forever

Calculate Load

2 min check
Advanced Options (Insulation/Windows)

Physics, Not Rules of Thumb

Old methods like "500 sq ft per ton" lead to oversizing, humidity issues, and short-cycling. We use the official ACCA physics model.

Official Compliance

Accepted by building inspectors. Our calculations verify compliance with 2026 SEER2 and A2L refrigerant safety limits.

Instant Results

No expensive software to install. No week-long wait for an engineer. Get your tonnage answer in under 2 minutes.

Free Forever

We believe energy efficiency should be accessible. Generate unlimited reports without a credit card.

Official DOE Standards

2026 Efficiency Requirements (SEER2)

Ensure your new equipment meets these federal minimums based on your region.

N

North Region

  • Air Conditioners ≥ 13.4 SEER2
  • Heat Pumps ≥ 14.3 SEER2
Most Strict
S

South Region

  • AC (< 45k BTU) ≥ 14.3 SEER2
  • AC (≥ 45k BTU) ≥ 13.8 SEER2
  • Heat Pumps ≥ 14.3 SEER2
SW

Southwest

  • AC + EER2 Requires high efficiency
    ≥ 14.3 SEER2
  • Heat Pumps ≥ 14.3 SEER2

⚠ Warning: Installing equipment below these standards is a federal violation and may void your warranty.

How It Works

Get your professional result in three simple steps.

1

Enter Home Details

Input basics like square footage, location, and ceiling height.

2

Select Insulation

Choose your insulation quality. Our algorithm handles the U-factor math.

3

Get Official Report

Instantly download a PDF report ready for permit applications.

Trusted by Pros & Homeowners

★★★★★

"I was quoted $8,000 for a 4-ton unit. This calculator showed I only needed 2.5 tons. Saved me huge money and the house cools perfectly."

JD
James D.
Homeowner, FL
★★★★★

"As a retired HVAC tech, I'm impressed. It matches my Wrightsoft numbers within 5%. Finally a free tool I can recommend."

RM
Robert M.
HVAC Technician
★★★★★

"Used the PDF for my permit in California. Inspector accepted it with no issues. Super easy to use."

SL
Sarah L.
DIY Renovator

Frequently Asked Questions

Is this accurate enough for a permit?
Yes. Our algorithm implements the ACCA Manual J (8th Edition) abridged procedure. It accounts for design temperatures, insulation, and solar gain. Thousands of homeowners have used our PDF reports for permit applications.
Why is my result smaller than my old unit?
Builders often oversize units to "be safe," but this actually hurts performance. Modern insulation and windows reduce the load significantly. A properly sized smaller unit runs longer cycles, removing more humidity and providing better comfort.
Does this work for Heat Pumps?
Absolutely. The load calculation (BTUs needed) is the same regardless of the equipment. Once you know your load (e.g., 36,000 BTUs), you can shop for any heat pump, gas furnace, or AC unit rated for that capacity.

Ready to Size with Confidence?

Don't guess with expensive equipment. Get the engineering-grade math for free.

No credit card required • Instant PDF • 2026 Compliant

The Science Behind Manual J

We don't just guess. We calculate using ASHRAE fundamentals.

Why "Rules of Thumb" Fail

Old logic suggested "500 square feet per ton," but this often leads to oversized equipment. Oversized units cycle on and off frequently (short-cycling), which results in high humidity, premature failure, and higher energy bills.

2026 Regulatory Update

As of January 2026, new strict efficiency (SEER2) and refrigerant (A2L) standards are in effect. This calculator is fully updated to check for compliance, ensuring your room volume is safe for the required system size (ASHRAE 15).