Dryer Vent Building Codes
Arizona Dryer Vent Code (Homeowner Guide)
Proper dryer venting moves moist, lint-laden air outdoors. Following code reduces fire risk, speeds drying, and protects warranties.
Arizona cities adopt codes locally, but most follow the International Mechanical Code (IMC §504) and International Residential Code (IRC §M1502).
This page is educational, not a substitute for your local building official or manufacturer instructions.
What the Code Says (Plain English)
1) Duct Material & Size
- Use smooth, rigid metal duct (min. No. 28 gauge), typically 4" diameter.
- Keep runs short and straight; avoid screws inside the duct.
2) Transition Duct (Dryer to Wall)
- Must be a single length listed to UL 2158A (often semi-rigid).
- Max 8 ft, cannot be concealed in walls/ceilings.
3) Termination (Outside Only)
- Vent to the outdoors with a backdraft damper; no screens allowed.
- Outlet at least 3 ft from doors, windows, or vented soffits (unless manual says otherwise).
4) Maximum Length
- 35 ft max from connection to outlet (before fittings).
- Deduct for elbows: −5 ft per 90°, −2.5 ft per 45°.
- If over 35 ft, post a label near the connection showing total length.
5) Independent System
- Dryer exhaust must be independent (not shared with bath fans or chimneys).
- No screws inside duct; seal per code—don’t trap lint.
6) Power Boosters
- If used, must be listed for dryer exhaust (UL 705) and installed per instructions.
Arizona Local Notes
| Jurisdiction | Current Adoption Snapshot | What it Means for Dryers |
|---|---|---|
| Phoenix | Adopted 2024 Phoenix Building Construction Code (I-Codes), effective Aug 1, 2025 (with grace period). | IMC §504 (2024) applies with local amendments. Use 3 ft clearance to openings, UL 2158A transition duct ≤8 ft, length rules & fittings table. |
| Scottsdale | Adopted 2021 IMC (with amendments). | Follow 2021 IMC §504—same core rules (35 ft base, elbow deductions, UL 2158A transition duct). |
| Tucson | Uses 2018 I-Codes with amendments. | IMC §504 (2018) language is similar for dryers: exhaust outdoors, backdraft damper, no screens, length & fittings table. |
Always verify with your city’s building department for the edition in effect at permit time.
Homeowner Quick Checklist
- Material: Rigid, smooth metal (4″). No screws poking inside.
- Transition: Single piece, UL 2158A-listed, ≤8 ft, visible (not inside walls).
- Route: Short & straight. Tally elbows (−5 ft per 90°, −2.5 ft per 45°).
- Termination: Outdoors with damper, no screen, ≥3 ft from openings if not specified by the manufacturer.
- Label (if long): If equivalent length >35 ft, post the length label within ~6 ft of the connection (when required by your code edition).
- Manufacturer first: If the dryer manual is stricter, the manual governs.
Estimate Your Equivalent Length
Uses the common IMC/IRC equivalent-length table (−5 ft per 90°, −2.5 ft per 45°). Your dryer manual or local code may have a different table.
FAQs
Can I vent into an attic, crawlspace, or garage?
No. Dryers must vent outdoors only, with a backdraft damper and no screen.
Can I use plastic or foil flex for the whole run?
No. The permanent duct should be rigid, smooth metal. The short transition from dryer to wall must be a single, UL 2158A-listed piece (often semi-rigid), max 8 ft and not concealed.
What if my route exceeds 35 ft?
Shorten the run, use long-radius fittings, or check whether your dryer’s manual allows a longer equivalent length. Some editions require labeling when >35 ft.
Roof vs. wall termination?
Both are permitted when detailed correctly. Use a listed cap with a damper, no screen, and maintain clearances.
Sources (Selected)
- International Mechanical Code (IMC) §504 (2021/2024 editions)
- International Residential Code (IRC) §M1502 (2021 edition)
- Phoenix: 2024 Phoenix Building Construction Code; effective Aug 1, 2025
- Scottsdale: Adoption of 2021 IMC (with amendments)
- Tucson: Adoption of 2018 I-Codes (with amendments)
- UL 2158A — Clothes Dryer Transition Duct
Last reviewed: Oct 7, 2025 (America/Phoenix).