Dryer installation guides include a chart for dryer vent maximum length, the longest exhaust run the dryer is rated to push air through, and the allowance shrinks with every 90-degree elbow. The chart is there because a dryer's blower can only move so much air against resistance, and a run that's too long leaves heat and lint in the duct instead of outside.
What the spec actually says
Both Whirlpool and LG use 4-inch rigid metal duct as the baseline and subtract length for each elbow:
| 90° elbows | Whirlpool 29-inch dryers, box or louvered hood | Whirlpool 29-inch dryers, angled hood | LG, 4-inch wall cap |
|---|---|---|---|
| 0 | 64 ft | 58 ft | 65 ft |
| 1 | 54 ft | 48 ft | 55 ft |
| 2 | 44 ft | 38 ft | 47 ft |
| 3 | 35 ft | 29 ft | 36 ft |
| 4 | 27 ft | 21 ft | 28 ft |
- •Whirlpool (installation instructions W10617663C): The guide calls for only 4-inch heavy metal vent and clamps, with no plastic or metal foil vent. Flexible metal vent is allowed only where it can be reached for cleaning, with a total length of no more than 7 3/4 feet. The exhaust hood must be at least 12 inches from the ground, and screws or tape that stick into the duct aren't allowed. Long vent models in the same guide are rated for much longer runs, from 120 feet with no elbows. Whirlpool says longer runs shorten dryer life and reduce drying performance.
- •LG: LG states that the maximum run should not exceed 65 feet, with 6 feet deducted for each additional elbow, and no more than four 90-degree elbows. Its own chart, shown in the table, drops faster than that 6-foot rule, so read the chart line for your elbow count. A smaller 2 1/2-inch wall cap opening cuts the allowance further, to 55 feet with no elbows. LG says to avoid plastic or vinyl duct.
Older guides differ. An older Whirlpool Corporation gas dryer guide (models RGD4100S and others) also listed flexible metal runs, such as 36 feet with no elbows and a box or louvered hood. Use the guide for your dryer, not a chart from another model.
Why manufacturers require it
- •Friction: Every foot of duct and every elbow slows the air. Past the rated length, the blower can't move enough air to carry moisture out.
- •Heat: Slow airflow keeps hot air in the drum and duct, so the dryer cycles its heat more and runs longer.
- •Lint: Slow air drops lint inside the duct, especially in elbows and low spots, which narrows the duct further.
- •Hood design: Hoods with smaller or angled openings add resistance, which is why the angled-hood column is shorter.
How to check your home against it
- Find your dryer's guide and note which chart applies to its model and hood type.
- Measure the duct from the back of the dryer to the outside hood, including vertical sections.
- Count every 90-degree turn, including the elbow right behind the dryer.
- Look at the outside hood. Note whether it's a box, louvered or angled style, and whether its flap opens freely.
- Check any flexible section. It should be metal, short and visible, not buried in a wall or ceiling.
- Compare your total with the chart line for your elbow count. If you're over, the run is out of spec.
What happens when it's ignored
- •Loads take two or more cycles to dry.
- •The dryer cabinet and laundry room run hot, and safety devices such as a thermal fuse can trip.
- •Lint builds up in the duct, which is a fire risk.
- •Moisture can condense inside a long, cool duct and drip back toward the dryer.
Closets add another limit on airflow. See laundry closet requirements.
When it needs a licensed pro
- •Rerouting a vent through framing, a floor or a roof is work for a contractor or a vent specialist. Ask your building department whether it needs a permit.
- •If the dryer is gas, any move of the dryer to shorten the run means disconnecting and reconnecting gas, which is a job for a licensed gas fitter or plumber.
- •Moving the dryer closer to an outside wall may mean a new outlet for a licensed electrician.
Sources
- •Whirlpool: 29-inch electric dryer installation instructions W10617663C (vent length chart; 4-inch metal; flexible limit; hood height)
- •LG: Dryer Proper Venting and Installation Tips (65-foot maximum; 6 feet per elbow; four-elbow limit)
- •Whirlpool Corporation: Gas dryer dimension guide 8562589 (older chart with flexible metal runs)
Quick check: Count your elbows first. With four, the Whirlpool and LG charts above allow only 27 or 28 feet of rigid duct, and less with an angled hood.
Vent in spec but loads still damp after a full cycle? Have the dryer itself looked at. Call TrueFix Long Island at (631) 985-3690 or book through our dryer repair page.