DRYER VENT CODE REFERENCE

To ensure compliance and fire safety for dryer vent systems:
1. Duct Material:
- Must be metal (typically rigid aluminum or galvanized steel).
- Flexible plastic or foil is not allowed for permanent installations.
2. Maximum Duct Length:
- Varies depending on dryer make and model, but IRC generally allows up to 35 feet, with deductions for elbows.
3. Termination:
- Must vent outdoors, not into attics, crawl spaces, or walls.
- Exterior termination must have a backdraft damper (no screen allowed).
4. Maintenance:
- Regular lint removal is critical.
- Commercial systems may require routine inspection per NFPA 1 or local fire codes.

1. IRC M1502 – Residential (1‑ & 2‑Family)

·       Independent duct per dryer; exhaust to outdoors.

·       Smooth metal ≥0.0157″ (28 ga), 4″ Ø.

·       Supports every 12 ft; screws ≤⅛″ protrusion.

·       Max length 35 ft minus 2.5 ft (45°) / 5 ft (90°) credits; label runs >35 ft.

·       Transition duct: UL 2158A, ≤8 ft, visible.

·       Termination: ≥3 ft from openings, back‑draft damper, NO screens.

·       No booster fans; power ventilators must be UL 705.

2. IMC 504 – All Occupancies

·       Follows manufacturer instructions first.

·       No screens or screws obstructing flow; fire/smoke dampers prohibited.

·       Supports every 4 ft; smooth metal ≥0.016″, 4″ Ø.

·       Transition duct same as IRC (UL 2158A, ≤8 ft).

·       Max length 35 ft with same elbow credits; label >35 ft.

·       Make‑up air needed if exhaust >200 CFM (≥100 sq in opening).

3. IMC 504.10 – Commercial Dryers

·       Fan motor outside airflow; continuous run or interlock.

·       6″ clearance to combustibles.

·       Single UL 2158A transition ≤8 ft, not concealed.

4. IMC 504.11 – Multistory Common Shafts

·       Rigid sheet‑steel ≥0.0187″ (26 ga) in fire‑rated shaft; NO offsets.

·       Continuous exhaust fan on standby power; alarm on failure.

·       12″×12″ cleanout at shaft base; system serves dryers only.

·       No screens at termination.

5. UL / Listing References

·       UL 2158A – flexible/transition ducts.

·       UL 705 – dryer‑duct power ventilators.

6. Protective Plates

·       Steel 0.062″ thick if duct <1¼″ from framing surface; extend 2″ above/below plate.

7. Manufacturer Precedence

·       Follow dryer manufacturer instructions where stricter than code.

8. Quick‑Check Table

·       Supports: IRC 12 ft   IMC 4 ft

·       Max base length: 35 ft

·       Elbow credits: 45° = 2.5 ft, 90° = 5 ft

·       Termination clearance: ≥3 ft from openings, ≥12.5 sq in open area

9. Field Checklist

□ Verify material/size and support spacing.

□ Measure equivalent length; label if >35 ft.

□ Inspect termination (damper, no screen).

□ Check transition duct (UL 2158A, ≤8 ft).

□ Confirm no booster fans.

□ For commercial/multistory: fan placement, continuous run, shaft integrity, alarms.