Contractors ask us this more than any other question: does my state require a Manual J? The honest answer is that it depends on which code your state adopted, which edition, what it amended, and how your local building department enforces it.
Where the requirement comes from
Most states base their residential building code on the International Residential Code. The IRC requires equipment to be sized with ACCA Manual S from Manual J loads (Section M1401.3) and ducts to be sized with Manual D (Section M1601.1). The International Energy Conservation Code repeats the equipment sizing requirement. When a state adopts these codes without removing those sections, the requirement comes along.
Why it varies
- Edition. States adopt different editions of the I-codes, on different schedules.
- Amendments. Some states modify or delete mechanical sections.
- State-written codes. A few states, Florida among them, publish their own codes and compliance forms.
- Local enforcement. Two counties under the same state code can ask for different paperwork, especially on replacements.
Where we see it most
In our work, new construction and additions almost always need a load calculation, and increasingly a duct design and an energy report. Like-for-like replacements are where local practice varies most. Strict jurisdictions such as Washington, DC review mechanical documentation closely.
How to check yours in five minutes
- Search your county or city building department’s mechanical permit checklist.
- Look for "Manual J", "load calculation", "Manual D" or "energy compliance".
- If the checklist is silent, call the permit desk and ask what they require for your project type.
- Or send us the address. We will tell you what that jurisdiction typically asks for.
Next step
Need a Permit docs?
Building departments want a complete, readable package. We assemble the calculations, schedules and drawings into one set, and we can draft clean plans from your hand sketches when there is no CAD file.
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