A DC rowhouse is long and narrow, and the laundry is rarely next to an outside wall. Machines end up in a basement under the front parlor, a closet off the second-floor hall or a kitchen corner, and the vent has to travel to the back of the house. Every dryer's installation guide has a chart that limits how far that trip can be. Exceed it and the dryer can't push enough air to dry clothes properly.
The charts, side by side
Whirlpool and LG both start from 4-inch rigid metal duct and cut the allowed length for each 90-degree elbow.
| 90° elbows | Whirlpool 29-inch, box or louvered hood | Whirlpool 29-inch, angled hood | LG, 4-inch wall cap | LG, 2 1/2-inch wall cap |
|---|---|---|---|---|
| 0 | 64 ft | 58 ft | 65 ft | 55 ft |
| 1 | 54 ft | 48 ft | 55 ft | 47 ft |
| 2 | 44 ft | 38 ft | 47 ft | 41 ft |
| 3 | 35 ft | 29 ft | 36 ft | 30 ft |
| 4 | 27 ft | 21 ft | 28 ft | 22 ft |
What Whirlpool adds
The Whirlpool 29-inch electric dryer guide sets the ground rules for the duct itself:
- •Only 4-inch heavy metal vent and clamps may be used. No plastic or metal foil vent.
- •Rigid metal is recommended for the best drying and to avoid crushing.
- •Flexible metal is acceptable only where it can be reached for cleaning, must be fully extended and supported, can't go inside enclosed walls, ceilings or floors, and should not exceed 7 3/4 feet in total.
- •Joints are sealed with clamps. No screws that poke into the duct and no duct tape.
- •45-degree elbows provide better airflow than 90-degree elbows.
- •The outside hood needs at least 12 inches of clearance from the ground or anything that could block it, such as plants or snow.
- •The exhaust must not go into a chimney, gas vent, wall, ceiling, attic, crawlspace or other concealed space.
The same guide includes a separate chart for long vent models: 120 feet with no elbows, dropping 10 feet per elbow to 70 feet with five. If you own one of those models, the chart for it is far more forgiving.
What LG adds
LG's venting article says the maximum run should not exceed 65 feet, to deduct 6 feet for each additional elbow, and to stop at four 90-degree elbows. The chart LG publishes (in the table above) falls faster than that 6-foot rule at some steps, so read the line for your elbow count. LG also says to avoid plastic or vinyl duct.
Older charts are different
An older Whirlpool Corporation gas dryer dimension guide for models such as the RGD4100S listed flexible metal runs too, allowing a straight 36-foot flexible run with a box or louvered hood. Newer guides restrict flexible metal to a short, visible transition. Always use the chart for the dryer you actually have.
Why length and elbows matter so much
A dryer's blower is sized to move a certain volume of air against a certain amount of resistance. Straight duct adds friction a little at a time. Each elbow adds a lot at once, because the air has to change direction. Past the chart's limit:
- •Moist air leaves too slowly, so loads take two cycles.
- •Heat stays in the drum and duct, and the dryer cycles its heater more often.
- •Lint settles in slow spots, especially elbows and sags, and the duct narrows over time.
- •In a long run through a cool basement, moisture can condense and drain back toward the dryer.
Hood style matters too. Angled hoods and smaller wall caps add resistance, which is why their columns are shorter.
Measuring a vent run
- Pull up your dryer's guide and pick the chart for its model and hood style.
- Measure every straight section, including vertical rises out of a basement.
- Count every 90-degree turn, starting with the elbow directly behind the dryer.
- Look at the outside termination. Note whether it's a box, louvered or angled hood, and check that the flap opens freely.
- Look hard at any flexible piece. Metal only, short, and in plain view rather than buried in a ceiling.
- Line your total up against the chart row for that number of elbows.
DC realities that affect the run
- •Front-to-back rowhouse runs. A basement laundry under the front of a row can be 40 feet or more from the rear wall before you count elbows. With three or four turns, many of these runs are outside the standard chart. A long vent model, relocating the dryer, or rerouting with fewer elbows are the usual answers.
- •English basements and areaways. The 12-inch clearance applies to the hood's surroundings. A hood in a below-grade areaway or behind trash bins can be blocked even when the duct is fine.
- •Historic districts. In places like Georgetown, Capitol Hill, Dupont Circle, Logan Circle and Mount Pleasant, exterior alterations are subject to historic preservation review. The DC Historic Preservation Office lists ventilating and mechanical installations among minor work it can review at staff level when visibility is limited, which is one reason rear walls are the usual choice for a new hood. Check with the office before cutting a new opening in a street-facing facade.
- •Condos and co-ops. Many buildings run dryer vents into shared risers or have specific rules about booster fans and duct material. Ask management before altering anything.
When to bring in a contractor
- •Rerouting through framing, floors or exterior masonry is contractor work. Ask the DC Department of Buildings whether your project needs a permit.
- •Moving a gas dryer closer to an outside wall means disconnecting and reconnecting gas, which in DC is done by a licensed gas fitter. See our notes on gas dryer hookups.
- •A new dryer location may need a new 240-volt outlet from a licensed electrician.
If the vent is short, clean and in spec and loads still come out damp, the dryer itself likely needs attention. Our dryer repair service checks heating elements, burners, thermostats and airflow sensors. For closets, read the rules for closet installations.
Documents referenced
- •Whirlpool 29-inch electric dryer installation instructions W10617663C: standard and long-vent charts, duct material, flexible metal limits, hood clearance, clamps.
- •LG: Dryer proper venting and installation tips: 65-foot cap, per-elbow deduction, no more than four elbows, chart by wall cap size.
- •Whirlpool Corporation gas dryer dimension guide 8562589: an older chart that still listed flexible metal.