Free estimate — verify against local code before building
HVAC Load Planning Calculator
Use this for early comparisons only. Never buy HVAC equipment from a square-foot estimate.
What this calculator includes
Compare how conditioned area, ceiling height, a broad climate band, envelope quality, windows, people, and sun affect a simplified whole-house planning index. This is not ACCA Manual J, does not produce a code-compliant design load, and cannot select equipment. Obtain a Manual J calculation made with ACCA-approved software, then use Manual S and manufacturer performance data before purchasing equipment or applying for a permit.
How to use this hvac planning index calculator
- 01
Enter conditioned area
Use only spaces served by the system and enter an average ceiling height. Exclude garages and unfinished spaces.
- 02
Describe broad conditions
Choose the closest climate band, envelope quality, and sun exposure. These are transparent planning multipliers, not Manual J inputs.
- 03
Inspect the math
Review the envelope and internal-gain steps. Equivalent tons are only BTU/h divided by 12,000 and are not a condenser size.
- 04
Commission the real design
Have a qualified professional run Manual J with approved software and select equipment with Manual S and OEM data.
Calculation sources and review
Primary references and formula assumptions are linked so you can verify them against the selected product, supplier, and adopted local requirements.
Internal formula review completed July 13, 2026. What this review covers
- ACCA Manual J residential load calculation (opens in a new tab)
The ANSI-recognized residential design-load standard.
- ACCA approved software directory (opens in a new tab)
ACCA says only listed software produces results compliant with its design standards.
- ACCA Manual S residential equipment selection (opens in a new tab)
Equipment selection uses the design load plus OEM performance data.
- 2024 IRC Chapter 14 — M1401.3 (opens in a new tab)
Equipment sizing is based on approved loads calculated under Manual J or another approved method and selected under Manual S or another approved method.
Frequently asked questions
Can square footage tell me what size AC to buy?
No. ACCA warns homeowners to be cautious when equipment is selected from square footage alone. A real load calculation accounts for local design weather, construction, glass, leakage, ducts, and room-by-room exposure.
What does equivalent cooling tons mean here?
It is only the displayed planning index divided by 12,000 BTU/h. The calculator does not round it to a catalog size and it must not be used to select a condenser or heat pump.
What is the difference between Manual J and Manual S?
Manual J determines the heating and cooling design loads. Manual S uses those loads, design conditions, and manufacturer performance data to select equipment.
Why can this planning number differ from Manual J?
This quick model does not know design temperatures, directional window areas and ratings, assembly U-values, air leakage, ventilation, latent load, or duct location and leakage. Those omissions can materially change a design load.
Does a valid result satisfy a permit office?
No. The 2024 IRC ties equipment sizing to approved load and sizing methods, and jurisdictions choose and amend the codes they adopt. Ask the local authority which documentation and software it accepts.