When Manual J Is Required by Code (And When It’s Not)
It's not just a "nice to have" recommendation anymore. It's the law in most states. Here is the breakdown.
For decades, Manual J was "recommended." Contractors ignored it.
Today, the International Residential Code (IRC) and International Energy Conservation Code (IECC) have made it mandatory.
Where is it Required?
Required in 100% of cases nationwide under IECC. You cannot get a building permit without submitting a Manual J Load Calculation (and typically Manual S and D as well).
If your jurisdiction requires a permit for an AC changeout (most cities do), they technically require a Manual J according to IRC M1401.3. However, enforcement varies wildly by inspector.
Replacing a capacitor, motor, or compressor does not require a new load calculation.
Why Contractors Skip It
Despite the law, many contractors skip it for replacements because inspectors rarely ask for the paperwork on a simple swap out.
The Risk: If you sell your home, a sharp home inspector may ask for the permit history. If the AC was replaced without a permit (or the permit is lacking the load calc), it can delay your sale or force you to pay for a retroactive permit.
Code Section M1401.3
"Heating and cooling equipment shall be sized in accordance with ACCA Manual S based on building loads calculated in accordance with ACCA Manual J..."
That is the law. Don't let a contractor tell you otherwise.
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