Measure the dryer vent and count its elbows. You get whether it is short enough by the building code and by Whirlpool's vent chart, and the longest duct each allows with your elbows.
Your dryer vent
Short enough: 25 ft of the code's 35 ftWhirlpool's chart: 21 ft of 44 ft · 10 ft of duct to spare by the code
Quick answer: by the building code a dryer duct can be 35 ft long, less 5 ft for every standard 90° elbow and 2 ft 6 in for every 45°, not counting the connector behind the dryer (IRC M1502.4.6.1). Two 90° elbows leave 25 ft of straight duct. The code also accepts the dryer maker’s own chart: Whirlpool allows 44 ft of vent with two 90° elbows and a box hood.
How to use the dryer vent length calculator
- Measure the duct: the rigid pipe from where the connector meets the wall to the hood outside, along its path.
- Measure the connector: the flexible piece from the back of the dryer to the wall.
- Count the elbows, 90° and 45°, in the whole run. A bend in the connector behind the dryer counts; a dryer that exhausts through its bottom counts one more 90°.
- Pick the kind of elbow and the hood. You get the vent’s length by the code’s count and by Whirlpool’s chart, and the longest duct each allows.
The rules behind the numbers
The building code
“The maximum length of the exhaust duct shall be 35 feet (10 668 mm) from the connection to the transition duct from the dryer to the outlet terminal. Where fittings are used, the maximum length of the exhaust duct shall be reduced in accordance with Table M1502.4.6.1. The maximum length of the exhaust duct does not include the transition duct” (2021 International Residential Code, M1502.4.6.1). The duct is 4″ metal with a smooth inside (M1502.4.1), held up at least every 12 ft, and never joined with screws that stick more than ⅛″ into it (M1502.4.2).
Or the dryer’s own chart
“The size and maximum length of the exhaust duct shall be determined by the dryer manufacturer’s installation instructions”, and the inspector gets a copy (M1502.4.6.2). Past 35 ft equivalent, a permanent label within 6 ft of the connection gives the duct’s length (M1502.4.7). Whirlpool’s chart is for 4″ rigid metal vent and counts the whole vent: “The total vent system length includes all straight and curved portions of the vent system.” For more elbows than its chart shows, “For 90° elbows, reduce the allowable vent system length by 10 ft (3.05 m). For 45° elbows, reduce the allowable vent system length by 6 ft (1.83 m)” (Whirlpool’s Dryer Venting Specifications).
The connector
The transition duct is one listed piece, “not greater than 8 feet (2438 mm) in length”, and never hidden inside a wall or ceiling (M1502.4.3). Whirlpool allows flexible metal vent only where it can be cleaned: “The total length should not exceed 7¾ ft. (2.4 m)”, fully stretched and supported, and never plastic or foil.
What an elbow costs by the code
| Elbow | 90° | 45° |
|---|---|---|
| Standard adjustable (4″-radius mitered) | 5 ft | 2 ft 6 in |
| Smooth, 6″ radius | 1 ft 9 in | 1 ft |
| Smooth, 8″ radius | 1 ft 7 in | 1 ft |
| Smooth, 10″ radius | 1 ft 6 in | 9 in |
Table M1502.4.6.1 of the 2021 IRC. A long, smooth bend lets far more duct through than a standard adjustable elbow.
Maximum dryer vent length by elbows
| 90° elbows | Code, standard elbows | Code, 10″-radius elbows | Whirlpool, box or louvered hood | Whirlpool, angled hood |
|---|---|---|---|---|
| 0 | 35 ft | 35 ft | 64 ft | 58 ft |
| 1 | 30 ft | 33 ft 6 in | 54 ft | 48 ft |
| 2 | 25 ft | 32 ft | 44 ft | 38 ft |
| 3 | 20 ft | 30 ft 6 in | 35 ft | 29 ft |
| 4 | 15 ft | 29 ft | 27 ft | 21 ft |
The code’s columns are the duct alone; Whirlpool’s are the whole vent, connector included (its Standard Vent System Chart, installation instructions W10443041B). Another maker’s dryer has its own chart.
Four worked examples
15 ft of duct, two 90° elbows, a 6 ft connector. 25 ft by the code’s count, 10 ft to spare; 21 ft of Whirlpool’s 44 ft.
30 ft of duct to a far wall. 40 ft by the code’s count, over its 35 ft, but 36 ft of Whirlpool’s 44 ft: the code accepts it with a Whirlpool dryer, its instructions on file and the duct labelled.
Four elbows and an angled hood. 34 ft by the code, within it, but 22 ft is over Whirlpool’s 21 ft for four elbows and an angled hood: a box hood allows 27 ft.
The 30 ft run with long, smooth elbows. Two 10″-radius 90° bends count 1 ft 6 in each, so the duct is 33 ft by the code’s count, within its 35 ft on its own.
Common dryer vent mistakes
- Forgetting the elbows. Two standard 90° elbows take 10 ft off the code’s 35 ft.
- Plastic or foil vent. Only 4″ metal; Whirlpool: “Do not use plastic or metal foil vent.”
- A long flexible hose. 8 ft at most by the code, 7¾ ft of flexible metal by Whirlpool, and never inside a wall.
- Screws through the duct. They catch lint; the code allows no fastener sticking more than ⅛″ inside, and Whirlpool none at all. Use clamps, not duct tape.
- A booster fan. Not allowed in a home dryer duct (M1502.4.5); a listed dryer exhaust power ventilator is, and its own instructions set the length (M1502.4.6.3).
- A screened hood. The hood needs a backdraft damper and no screen, at least 3 ft from openings into the house unless the dryer’s instructions say otherwise (M1502.3), and 12″ above the ground (Whirlpool).
Before hooking a dryer to an existing vent, clean the lint from its whole length and check the hood is not plugged (Whirlpool). Check the space for the machines with the washer and dryer space calculator, and draw the laundry room to scale in the free 2D planner.
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- Laundry room layout ideas
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- Basement laundry room ideas
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Dryer vent length questions
How long can a dryer vent be?
35 ft by the building code, less 5 ft for each standard 90° elbow and 2 ft 6 in for each 45°, not counting the connector (IRC M1502.4.6.1), or as long as the dryer’s own instructions allow. Whirlpool’s chart allows 64 ft of rigid vent with no elbows and a box hood, 44 ft with two 90° elbows.
What is the maximum dryer vent length?
By the code, 35 ft of duct minus the elbows’ equivalent lengths. By Whirlpool’s chart, 27 to 64 ft of 4″ rigid metal vent with a box or louvered hood, and 21 to 58 ft with an angled hood, for four to no 90° elbows.
How long should a dryer vent hose be?
As short as it can be: the connector from the dryer to the wall is 8 ft at most by the code and never inside a wall (M1502.4.3); Whirlpool allows 7¾ ft of flexible metal, fully stretched.
How much does an elbow reduce dryer vent length?
By the code, a standard adjustable 90° elbow counts 5 ft and a 45° 2 ft 6 in; smooth elbows count 1 ft 6 in to 1 ft 9 in for a 90° and 9 in to 1 ft for a 45° (Table M1502.4.6.1). Whirlpool takes 10 ft off its chart for each 90° past four, and 6 ft for each 45°.
Can a dryer vent be longer than 35 feet?
Yes, where the dryer’s installation instructions allow it: the code accepts the maker’s length (M1502.4.6.2), with the instructions given to the inspector and a label within 6 ft of the connection giving the duct’s length (M1502.4.7).
Can I use a booster fan on a long dryer vent?
Not a booster fan (M1502.4.5). A dryer exhaust duct power ventilator listed to UL 705 is allowed, and its own instructions then set the duct’s length (M1502.4.4, M1502.4.6.3).