If your dryer suddenly needs two cycles to dry a normal load, that’s not just annoying—it’s a warning. The U.S. Fire Administration estimates about 2,900 home clothes dryer fires occur each year, and failure to clean the vent is a leading cause. Even if nothing ignites, a clogged vent wastes energy, shortens the life of your appliance, and leaves your laundry room hot and humid. You don’t need to drag the dryer away from the wall to figure out what’s going on. With a few simple observations and tests, you can tell whether airflow is restricted and decide whether it’s time to clean the duct or call a pro. Expect practical checks you can do today, the telltale signs most people miss, and clear next steps that keep your home safe and your dryer working like it should.
Quick Answer
Run the dryer and check airflow at the exterior vent: the flap should open fully and strong, warm air should blow out—enough to vigorously move a tissue held a few inches away. If airflow is weak, dry times have suddenly increased, the dryer’s cabinet feels unusually hot, or you notice a burnt-lint smell, your vent is likely clogged even without moving the machine.
Why This Matters
A dryer is basically a heater plus a fan. When the vent clogs, hot, moist air has nowhere to go, so the dryer runs longer and hotter. That raises fire risk and drives up energy bills. For a family of four doing 5 loads per week, an extra 20 minutes per load adds roughly 87 hours of runtime per year. At 2–3 kWh per cycle, that’s easily $60–$120 in wasted electricity annually, and more wear on bearings, belts, and the heating element.
There’s also the moisture angle. Restricted exhaust leaves the laundry room steamy, which can fog windows, swell wood trim, and encourage mildew. I’ve seen paint bubble near a vent hood simply because the flap never opened and moist air pushed back into the wall cavity. And then there’s safety: lint is highly flammable, and when airflow drops, temperatures spike at the heater and in the duct. That combination is exactly what causes thousands of dryer fires every year. Catching a clog early protects your home, your budget, and your appliance.
Step-by-Step Guide
Step 1: Confirm longer dry times and unusual heat
Run a normal load (towels work well) on your usual setting. If the load that used to finish in ~45 minutes now needs 70–90 minutes, or clothes feel hot but still damp, that’s a classic sign of restricted airflow. While the cycle runs, place your hand on the dryer’s top and sides—warm is normal, but noticeably hot to the touch points to trapped heat. You might find dryer vent cleaning brush helpful.
- Tip: Use a kitchen timer and jot down cycle lengths for consistency.
- Pro note: Many dryers monitor airflow and will display codes like “AF” when it’s restricted; don’t ignore them.
Step 2: Check exterior vent hood airflow
With the dryer running, go to the outside termination hood. The damper flap should open fully and blow steady, warm air. Hold a tissue or thin paper 2–4 inches from the opening; it should flap vigorously or blow away. If you have an anemometer, expect roughly 1,000–1,700 feet per minute at a 4-inch duct—significantly lower suggests a restriction.
- Warning: Some hoods have bird guards that trap lint. If the cage is matted over, airflow will be weak even if the duct beyond is clear.
- Listen for chattering or a flap that barely moves—both hint at low flow.
Step 3: Smell and humidity check in the laundry area
Stand near the dryer during the last half of the cycle. A hot, slightly “linty” smell is normal; a sharp, scorched odor or a musty, steamy room is not. Foggy windows, damp walls, or condensation on cold surfaces mean moist air isn’t escaping properly. You might find dryer vent cleaning kit helpful.
- Tip: A simple hygrometer should stay near normal indoor humidity. Spikes during drying indicate exhaust problems.
Step 4: Inspect for visible lint at the vent and around the dryer
Look for lint clinging to the exterior hood, stuck behind the flap, or blown onto nearby siding. Inside, check the lint screen and the door seal area. Excess lint where it shouldn’t be often means the path to the outdoors is restricted, causing lint to settle in odd places.
- Pro tip: Rinse your lint screen under water. If water pools instead of flowing through, clean it with hot water and a drop of dish soap; a coated screen worsens airflow issues.
Step 5: Rule out simple obstructions without moving the dryer
From the outside, clear any lint blanket on the hood or bird guard. Verify the damper moves freely by gently lifting and releasing it. Indoors, make sure the laundry room door is open and a supply grille isn’t blocked; modern homes can be so tight that the dryer starves for make-up air, mimicking a clog. You might find dryer lint vacuum attachment helpful.
- Warning: If airflow remains weak after these checks, stop using the dryer until the duct is cleaned. Overheating is a real risk when the vent is restricted.
Expert Insights
Field reality: most “my dryer’s not drying” service calls trace back to vent restrictions, not failed heaters. A dryer is designed around a certain airflow—roughly 100–200 CFM. Even a partial blockage drops that below the threshold where moisture can be carried out, so clothes stay damp and the machine runs hotter trying to compensate.
Common misconception: “I feel some air outside, so the vent is fine.” Not necessarily. The damper should snap open decisively and stay open; a lazy flap or air you’d describe as a gentle breeze is a red flag. Another myth is that longer cycles are just ‘old dryer’ behavior. In reality, poor venting burns out heaters and elements early, which then makes things worse.
Pro notes worth knowing: long, convoluted runs are trouble even when clean. Most manufacturers cap vent length at about 35 feet equivalent for 4-inch duct; every 90° elbow counts as ~5 feet, each 45° as ~2.5 feet. Flexible foil or plastic ducts crush easily and collect lint at ridges—use smooth-wall metal only. If your dryer throws an airflow (AF) code, or the exterior hood barely opens, treat it like a warning light: pause laundry, schedule a cleaning, and consider upgrading the hood to a low-resistance model.
Quick Checklist
- Time a normal load and compare to your usual dry time.
- Feel the dryer’s top and sides; note if they’re unusually hot.
- Check the exterior vent; the flap should open fully.
- Hold a tissue at the vent—air should blow it strongly.
- Look for lint matting on the vent hood or bird guard.
- Smell for scorched-lint odors during the cycle.
- Watch for condensation or steamy air in the laundry room.
- Listen for rattling or whistling that signals low airflow.
Recommended Tools
Recommended Tools for how to tell if your dryer vent is clogged without removing the dryer
Frequently Asked Questions
How can I tell if it’s the lint screen or the vent causing slow drying?
Start with the lint screen: rinse it under water. If water puddles on top, there’s a film from dryer sheets—clean it with hot water and a little dish soap, then dry it fully. If airflow and dry times don’t improve after this, the issue is likely downstream in the vent.
Is it safe to keep using the dryer if the vent seems clogged?
It’s not safe. Restricted vents cause overheating and can ignite lint. If the exterior flap barely opens or you notice a burnt smell, stop using the dryer until the duct is cleaned. Running more cycles won’t solve it and may damage the appliance.
What should airflow feel like at the exterior vent?
With the dryer running, expect strong, steady, warm air—enough to open the flap fully and make a tissue dance from a few inches away. If it feels like a gentle breath or the flap only quivers, airflow is below normal and you likely have a blockage or an overly long, restrictive run.
Can a gas dryer create extra risks when the vent is clogged?
Yes. Gas dryers produce combustion products that must be vented; a clogged duct can cause elevated carbon monoxide in the laundry area. If you have a gas dryer and suspect poor venting, stop using it immediately and ventilate the space until the duct is cleared.
My dryer is new—could the vent still be the problem?
Absolutely. A brand-new dryer can’t overcome a bad vent. If the run is long, crushed behind cabinets, or has multiple elbows, airflow drops even when clean. New dryers often monitor airflow and may show an ‘AF’ or similar code if the vent is the bottleneck.
How often should I clean the dryer vent to avoid clogs?
As a baseline, once per year for typical households. If you do heavy laundry (pets, multiple loads weekly), have a long or complex vent run, or notice lint at the exterior hood sooner, clean it every 6 months. The lint screen should be cleaned every load.
Will a booster fan fix weak airflow if the run is long?
A booster fan can help long runs, but it should be purpose-built with a pressure switch and installed per code. It’s not a bandage for a clog. If airflow is weak due to lint accumulation, adding a fan may mask the problem and create a fire hazard.
Conclusion
The fastest way to spot a clogged vent—without moving the dryer—is to check exterior airflow and watch for the supporting signs: longer cycles, excess heat, lint around the hood, and steamy air. If the flap barely opens or a tissue barely moves, pause laundry and plan a vent cleaning. Clear any obvious lint at the hood, verify the damper moves freely, and schedule a thorough duct sweep if airflow stays weak. A few minutes of checking today can save your dryer, lower your bills, and keep your home safe.
Related: For comprehensive information about Ventisafe, visit our main guide.