A clothes dryer must vent to the outdoors. Not into the attic, not into a crawlspace, not into the garage, and not into a bucket of water behind the machine. We still find all four in Wonder Lake houses, usually in finished basements and additions where somebody solved a routing problem the fast way. Each one causes predictable damage, and none of them are hard to correct.
By Johnathan Mason, Ace Chimney Service.
Why an interior termination is a problem
A dryer load moves a substantial amount of water out of your clothes as vapor, plus lint and heat. Dumping that into an enclosed interior space does three things.
Moisture. Warm, wet air hitting cold attic sheathing in a McHenry County January condenses immediately. Repeated over a winter, that produces damp insulation, stained sheathing and mold growth. Homeowners usually blame a roof leak, because that is exactly what it looks like.
Lint accumulation. Lint is fine, dry, highly combustible cellulose. Venting into an attic distributes it across the insulation near the duct outlet. Lint in an attic is not a theoretical fire concern.
Combustion safety. A gas dryer’s exhaust contains combustion byproducts. Venting a gas dryer into any interior space is unsafe, full stop, and that includes attached garages.
The specific case of attached garages
Venting into an attached garage is common because the duct run is short and the wall is right there. It is still wrong. Beyond the moisture and lint, garages are where people store gasoline, solvents and paint, and the separation between a garage and living space exists for a reason. A duct that penetrates into the garage also compromises that separation.
What a correct termination looks like
The duct should be rigid or semi-rigid metal, as short and straight as practical, and end at an exterior hood with a backdraft damper. That hood should have a flap or louvers, not a screen. Screens catch lint and clog, which is the opposite of what you want.
The termination needs clear space around it. We find hoods buried behind shrubs, blocked by a deck, or terminating a few inches from grade where snow covers them by January. A blocked exterior hood produces the same symptoms as a clogged duct, and a surprising number of calls about a dryer taking three cycles turn out to be a snowdrift.
Foil accordion duct is the other common finding. It traps lint in its ridges, crushes behind the machine, and is not appropriate for a concealed run. We cover both duct type and routing on our dryer vent cleaning page.
How to check yours in ten minutes
Run the dryer on a warm setting and walk the outside of the house. Find the hood. You should feel strong, warm airflow and see the damper standing open. Weak airflow means restriction somewhere between the machine and that hood.
If you cannot find an exterior hood at all, that is the answer: the duct terminates somewhere it should not. Check the attic above the laundry room and the garage wall behind it.
Then pull the machine out and look at the connection. Crushed duct behind the dryer is the single most common restriction, and it is created every time the machine gets pushed back against the wall.
Fixing it properly
Correcting an interior termination means running new rigid duct to an exterior wall or roof and installing a proper hood. The route determines the difficulty. Sometimes it is a short punch through a rim joist, and sometimes it means working around framing across a finished ceiling.
While the duct is open is also the right moment to clean the whole run rather than just relocating years of packed lint.
Ace Chimney Service has worked on chimneys, fireplaces and vents across Crystal Lake and McHenry County for 29 years. We are insured and bonded, we price the work up front before anyone starts, and we answer the phone seven days a week from 7 AM to 7 PM at (815) 320-0883.
Frequently asked questions
Can I vent my dryer into the attic if I add a filter?
No. A filter catches some lint but does nothing about the moisture, which is the larger problem. Dryers must vent outdoors.
What about those indoor lint traps that use water?
They are sold for electric dryers, but they release all the moisture into the room. In an already humid basement that is a poor trade, and they must never be used with a gas dryer.
Is it acceptable to vent into a crawlspace?
No, for the same reasons as an attic. Crawlspaces are usually colder and less ventilated, so moisture problems there develop faster.
How do I know if my dryer is gas or electric?
Look behind it for a gas line and shutoff valve, or check the plug, since electric dryers use a large 240-volt plug. If a gas line is present, an interior termination must be corrected immediately.
Should the exterior hood have a screen?
No. Screens trap lint and clog quickly. A hood with a hinged flap or louvered damper is correct, and it keeps birds out well enough in practice.
How long can the duct run be?
Manufacturers publish a maximum equivalent length, and every elbow subtracts from it. Long runs with several bends need to be kept unusually clean to perform.
My hood is close to the ground and snow covers it. Is that a problem?
Yes. A buried hood blocks exhaust and can push moisture back along the duct. It should be relocated higher or given clearance.
How often should the duct be cleaned?
Once a year is a reasonable baseline for a typical household. Long runs, several elbows, or heavy laundry volume justify more frequent attention.
Published October 4, 2026