Clean the lint screen every load, and have the whole dryer vent, from the back of the dryer to the outside hood, cleaned at least once a year. Do it sooner if loads take longer than usual to dry or the outside flap doesn't open while the dryer runs. Fall is a good time for it: dryer fires are more common in the colder months, and in many Philadelphia rowhomes the vent run is longer and harder to reach than people expect. A short, straight vent behind a basement dryer is often a do-it-yourself job. A long run through a finished ceiling or up to the roof usually is not.
This is general safety information from federal fire and product-safety sources, not a substitute for your dryer's installation manual, which has the final word on venting your model.
Why the vent matters more than the lint screen
The U.S. Fire Administration's report on clothes dryer fires in residential buildings (data from 2008 to 2010, the most recent USFA has published on the topic) estimated about 2,900 such fires a year, with failure to clean as the leading factor contributing to ignition, at 34 percent. Dust, fiber and lint were the most common items first ignited. The same report found that these fires were more frequent in the fall and winter, peaking in January.
The lint screen catches most of the lint, not all of it. USFA explains that lint also travels through the vent with the moist air, builds up in the duct, reduces airflow and can lead to overheating. Bird and animal nests and crushed or damaged ducts block the vent the same way. So a clean screen doesn't mean a clean vent.
Signs your dryer vent is clogged
The Consumer Product Safety Commission's safety alert on overheated dryers and USFA's dryer fire safety flyer point to a few things you can check yourself:
- Clothes are still damp at the end of a normal cycle.
- Drying takes longer than it used to.
- No air at the outside vent. Go outside while the dryer is running. You should feel warm air and see the flap or louvers open. If not, the duct or the hood may be blocked.
- The duct behind the dryer is crushed, kinked or torn. USFA's flyer says to check that the venting isn't damaged, crushed or restricted.
- Lint piling up behind the dryer or around the outside hood. CPSC says to clean behind the dryer, where lint collects.
If you notice a burning smell or the dryer cabinet gets unusually hot, stop using it until it has been checked.
Where the vent goes in a Philadelphia rowhome or twin
Many older Philadelphia homes didn't have a laundry room when they were built, so the dryer ended up wherever a later owner could fit it. That decides how hard the vent is to clean.
- Basement laundry. Often the easiest case: a short duct out through the front or rear foundation wall. Watch for hoods that end up close to the ground, under the front steps or behind a rear yard fence, where leaves and lint pile up.
- Laundry on an upper floor or in a rear addition. Common after renovations. The vent may run several feet between floor joists or above a ceiling, and then out a side or rear wall.
- Roof terminations. Some upstairs dryers vent up through the roof. Lint collects in the roof cap and at the top of the vertical run, and getting to it means going up on the roof. If you have a flat roof, check the dryer cap whenever you check the roof drains; our flat roof maintenance guide covers the rest of that inspection.
If you don't know where your vent comes out, run the dryer and walk around the outside of the house and, if you can do it safely, look at the roof.
What a safe dryer vent looks like
The Department of Energy's Building America Solution Center summarizes the dryer exhaust rules of the International Residential Code in its guide to proper clothes dryer venting. Philadelphia's residential code is based on the IRC. In short:
- Metal duct. Rigid or semi-rigid metal duct, usually 4 inches in diameter. CPSC recommends replacing plastic or foil accordion-style duct with rigid or corrugated semi-rigid metal, because the flexible kind traps lint more easily and kinks or crushes.
- Short and straight. The guide gives a maximum of 35 feet, reduced by 2.5 feet for every 45-degree bend and 5 feet for every 90-degree bend, unless the dryer manufacturer specifies a different length. So a run with three 90-degree elbows is limited to 20 feet of straight duct. Long rowhome runs can hit that limit fast.
- No screws through the duct. Screws that poke into the duct catch lint. Joints go in the direction of airflow and are held with clamps or foil tape.
- A damper, not a screen, at the outside. The hood needs a flap or louvered damper that closes when the dryer is off. A screen over the opening is not allowed because it clogs with lint.
- Outside, not indoors. Dryers must vent directly outdoors (ventless models with a condensate drain are the exception), at least 3 feet from doors, windows and other openings. The guide warns that a vent emptying into a crawl space, attic or other building cavity creates a significant risk of moisture damage.
How to clean a short dryer vent yourself
For a basement dryer with a short, reachable run, this is a reasonable weekend job:
- Unplug the dryer. For a gas dryer, also close the gas shutoff valve behind it. Don't disconnect or bend the gas connector if you aren't comfortable doing it; that part is gas work.
- Pull the dryer out gently. Don't yank it so hard that you crush the duct or strain the gas line.
- Disconnect the duct from the back of the dryer and from the wall connection. CPSC notes that clearing a blockage may require this step.
- Clean the duct and the dryer's outlet with a dryer vent brush kit and a vacuum. Work from both ends if you can reach the outside hood.
- Clean the outside hood. Remove lint, leaves and any nest material, and make sure the flap or louvers swing freely. Don't add a screen.
- Vacuum behind and under the dryer, and the lint screen slot.
- Replace any plastic or foil duct with metal while it's apart.
- Reconnect everything to the dryer and the outside vent before you use it again, as CPSC reminds people. Reopen the gas valve for a gas dryer.
- Test it. Run the dryer on air or low heat and check for strong airflow at the outside hood.
CPSC also recommends having a qualified service person clean the inside of the dryer cabinet periodically. That's a separate job from the duct, and it's one to leave to a technician.
The same Building America guide recommends that gas dryers be cleaned and serviced regularly by a professional, and that you install a carbon monoxide alarm in the laundry area if your dryer burns gas. Our smoke and CO detector guide covers where alarms go in a Philadelphia home.
There's a basement-specific point too. In many rowhomes the dryer sits a few feet from a gas water heater or boiler that vents up the chimney. The guide warns that when a room with that kind of appliance becomes depressurized, exhaust byproducts can be pulled back into the room. A dryer pushes a lot of air out of a small basement, so if the laundry area is a tight, closed-off room, ask whoever services your heater or boiler to look at the combination.
If you ever smell gas, leave the house and call PGW (or PECO in the suburbs) from outside. Moving or replacing the gas connection is a job for a pro; L&I's plumbing permit page explains when plumbing work needs a permit and points to 311 for questions.
Everyday habits that keep the vent clean
From the CPSC and USFA guidance:
- Clean the lint screen before or after every load, and never run the dryer without it.
- Don't start a load and then leave the house.
- Take care with clothes soiled with gasoline, cooking oil, cleaning agents, or finishing oils and stains. CPSC suggests washing them more than once and hanging them to dry. If you must machine-dry them, use the lowest heat and a cycle with a cool-down period, and don't leave them piled in the dryer or a basket afterward.
- Keep the area around the dryer clear of boxes, laundry and clutter.
Checklist
- Lint screen cleaned every load.
- Outside hood found, and the flap opens with strong airflow while the dryer runs.
- No plastic or foil accordion duct anywhere in the run.
- Duct not crushed behind the dryer; leave a little space or use a wall recess.
- Whole vent cleaned within the last year, and the date written down.
- No screen on the outside hood, and no nests.
- Working smoke alarm on the laundry level, and a CO alarm in the laundry area if the dryer burns gas.
When to call a pro
Hire a dryer vent cleaning or appliance technician when:
- the vent runs through a finished ceiling or wall and you can't see its whole length;
- it vents through the roof, or the outside hood is out of safe reach from the ground;
- cleaning didn't fix long drying times, which can point to a crushed section, a duct that is too long, or a problem inside the dryer;
- the duct needs to be rerouted, shortened or replaced with rigid metal through framing;
- it's a gas dryer and you'd have to move or disconnect the gas line;
- the dryer itself overheats, smells hot or shuts off mid-cycle.
When you ask for an estimate, say where the dryer is, where the vent comes out (wall or roof, which side of the house), roughly how long the run is, whether it's gas or electric, and the drying problem you've noticed. Photos of the back of the dryer and the outside hood help a lot. What drives the cost is mostly access: a short basement run is quick, while a long run behind finished walls, a roof cap or a full replacement with rigid duct takes more time and material.
You can post the job on HomeKept for appliance repair in Philadelphia. It's free for homeowners: describe it once and compare up to three estimates from local pros. If you're already lining up small jobs before winter, our fall home maintenance checklist has the rest of the list.
HomeKept is a brand of FalconAI LLC, 331 E Street Rd, Feasterville-Trevose, PA 19053.
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