Compare Uniform Plumbing Code sizing logic for hydromechanical grease interceptors (HGI) versus gravity grease interceptors (GGI)

Steps

1. Search IAPMO's 'Answers and Analysis' portal (aa.iapmo.org) for UPC Chapter 10 interpretations on interceptor sizing
2. Confirm the jurisdiction's adopted UPC edition and chapter/section numbers before citing, since section numbering has shifted across UPC editions
3. Note that HGIs are rated and sized in gallons-per-minute (GPM) flow capacity while GGIs are sized by liquid holding volume in gallons, reflecting two different separation mechanisms (hydromechanical baffling/flow control vs. gravity settling over a longer detention time)
4. Apply the general industry sizing convention that total fixture drainage capacity connected to an HGI should not exceed roughly 2.5 times the interceptor's certified GPM rating, verifying this ratio against the specific adopted code edition rather than assuming it universally
5. For GGIs, confirm the applicable code's minimum detention time (commonly around 30 minutes) and minimum volume threshold with the local plumbing official, since values vary by edition and local amendment
6. Verify which fixtures are exempt or included in the sizing calculation (e.g., dishwashers, floor drains) against the locally adopted code text