Grease duct horizontal run with slope
Drainage-controlled horizontal run
The approved design, adopted code, qualified procedure, and exact manufacturer instructions control this installation.
Before you start
- Grease duct is a fire/life-safety system. Verify the approved design, adopted code, hood and fan requirements, listed enclosure or shaft details, and inspection hold points before fabrication or installation.
- Confirm the required drainage direction, approved collection or drain point, support elevations, access locations, and whether the system is welded or listed modular.
- Field-check the route for beams, offsets, and fittings that could create a low pocket.
- Verify the slope requirement from the adopted code and approved design rather than using a remembered number.
- Stage adjustable supports, level or laser, joint materials, access components, and inspection tools.
Tools and materials
Grease-duct sections and fittings, adjustable noncombustible supports, laser or digital level, approved welded or listed joint components, access doors or cleanouts shown on the design, marker, tape, and inspection light.
Lay it out
- Mark the high and low points of the run and establish each support elevation before duct is lifted.
- Carry the drainage direction through elbows, transitions, and offsets instead of sloping only the straight sections.
- Place access points where cleaning personnel can reach changes of direction and low collection areas.
Set and support it
- Install and adjust all supports to the planned drainage line before making permanent joints.
- Support every fitting body so it cannot sag into a grease pocket.
- Keep sections independently supported while alignment and joint work are completed.
Make the connection
- 1
Set the first section at the verified high or low reference point.
- 2
Install each following section to the planned support elevation.
- 3
Check the drainage direction continuously with a level or laser before closing each joint.
- 4
Complete the approved welded or listed modular connection.
- 5
Recheck the run after joint completion and support loading.
- 6
Install access, drain, or collection components shown on the approved design.
- 7
Complete required inspection before enclosure or concealment.
Check the install
- The run drains continuously toward the approved point with no reverse slope or belly.
- Fittings and transitions continue the intended drainage path.
- Supports are secure and do not settle the run into a low pocket.
- Access doors and cleaning points remain reachable.
- All joints are liquid-tight and inspected.
Common mistakes
- Checking slope only at the beginning and end while a middle hanger creates a belly.
- Allowing an elbow or transition to become the lowest point with no approved drainage or access.
- Adjusting slope after rigid joints are complete and loading the connections.
- Guessing the required slope instead of verifying the project requirement.
Stop and ask
Stop if the route cannot maintain continuous drainage, the approved drain or collection point is unclear, access cannot be provided, or a structural conflict forces a low pocket.