TinnerFlow logoTinnerFlow™
Apprentice Q&A · #112

How do I layout a welded grease duct slope so grease drains toward the hood?

3rd YearSpecialty DuctRED · Stop / Verify

Horizontal grease duct runs under 75 feet long must slope a minimum of 4 1 inch per linear foot (2% slope) back toward the commercial hood or an approved grease reservoir collection trap. If the horizontal run exceeds 75 feet, the slope must increase to at least 1 inch per linear foot.

Search Field RescueOpen in Q&A search

Plain-English answer

Horizontal grease duct runs under 75 feet long must slope a minimum of 4 1 inch per linear foot (2% slope) back toward the commercial hood or an approved grease reservoir collection trap. If the horizontal run exceeds 75 feet, the slope must increase to at least 1 inch per linear foot.

Field checklist

Ask Foreman

Hey boss, I’m on specialty duct and need verification before I touch this: How do I layout a welded grease duct slope so grease drains toward the hood? Do you want me to stop here and check the approved detail, submittal, or inspector/manufacturer requirement first?

Open Ask Foreman

Verify before acting

Use this as training guidance. The foreman, approved drawings, project specs, manufacturer installation instructions, employer safety policy, and AHJ/code requirements always control the final answer.

Related questions

#115 · What's the trick to installing fire-wrap (Zero Clearance insulation) on grease duct?3rd Year · Specialty Duct#111 · What is the required clearance to combustibles for a Type 1 grease duct (black iron)?3rd Year · Specialty Duct#118 · How do I install a cleanout access door in a welded grease duct?3rd Year · Specialty Duct#114 · How do I test a welded grease duct system for leaks (light test vs. water test)?3rd Year · Specialty Duct#113 · What is the proper welding procedure (MIG vs. TIG) for 16-gauge stainless steel duct?3rd Year · Specialty Duct#116 · How do I handle and install exposed double-wall spiral duct without scratching it?3rd Year · Specialty Duct

Related Field Rescue routes

What do I do when slope direction wrong on horizontal grease duct?Field Rescue · Grease Duct, Kitchen Exhaust & Industrial ExhaustWhat do I do when forgetting slope/drainage needs on special exhaust?Field Rescue · Measuring, Field Verification & Layout MarksWhat do I do when wrong slope/drainage on kitchen exhaust?Field Rescue · Grease Duct, Kitchen Exhaust & Industrial Exhaust

Related mistakes & recovery checks

#114 · Fabricating kitchen exhaust grease duct without slope toward the grease trap3rd Year · Sheet Metal Work#118 · Hanging a coil section without checking drain pan tilt toward the drain connection3rd Year · Installation#021 · Running the seam in the wrong direction, trapping water or allowing leakage1st Year · Sheet Metal Work