Dad will tell you the dryer is fine because he empties the lint trap every time. I believe him. The trap does its job, but it cannot reach the long run of duct that carries the warm air out through the wall. Lint that gets past the trap settles in that duct a little at a time. Eventually the clothes need two cycles to dry, and the back of the dryer runs warm. This is an easy job to put off and an easy one to hire out, so here is how I would walk it from the first phone call to the last look at the outside flap.

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What to do tonight

Go into the laundry room with a flashlight and look at the back of the dryer. Note what kind of duct comes out of it: stiff metal, a flexible foil tube, or a plastic accordion hose. Write it down. Then find where the duct goes through the wall or ceiling, and look at the outside cover if you can see it from the yard. Take a photo of both. The person who comes will want them, and it saves a phone call later.

Run the dryer on air fluff for a few minutes, then go outside and check whether the flap at the vent opens and a steady stream of air comes out. If the flap does not move or only a weak puff comes out, write that down too. If the dryer runs on gas, do not pull it away from the wall yourself. Leave the connection to the person doing the work.

Decide who does the work

You have two main choices: a company that specializes in dryer vents, or a handyman. A specialist usually brings a brush or vacuum that reaches the full length of the run and can show you what came out. A general handyman may clear what he can reach but may not be set up for a long run. Ask each one the same questions. Do you clean the whole duct from the dryer to the outside cover? Do you clean the outside cover and the flap? Will you move the dryer, and if so, who reconnects it? If the dryer runs on gas, ask who reconnects the line and whether that person is licensed to do it where you live. Will you run a test cycle before you leave? Will you give me a written note of what you found? Compare the answers, not the sales talk.

Booking the visit

When you call, give them the dryer's make and model if you can read the sticker inside the door, the type of duct from your notes, and whether the dryer is gas or electric. Ask whether they need the dryer pulled out from the wall and whether there is an access panel if the duct runs through a ceiling or wall. Ask what they do if they find a duct that is crushed, disconnected, or too long for their equipment. You want to know that before the crew has the dryer in the middle of the room.

Pick a morning when Dad is home and can watch. He does not need to help with the work. He needs to see it so he trusts the result, and he needs to be there so the technician can ask where the dryer goes back. If you live far away, ask a neighbor or another family member to be at the door for the visit too.

The visit itself

Stay in the laundry room while the technician pulls the dryer out and checks the connection, the duct, and the wall behind it. Ask to see the lint that came out and the outside cover before anything is closed up. Ask them to start the dryer on a short cycle and go outside to watch the flap open. A good result is a steady flow of warm air, a flap that moves freely, and no clogged mesh at the cover. Ask them to set the dryer square against the wall with the duct not bent or kinked behind it. Do not let them leave until you have seen both ends of the duct working.

When to call the company back

Call them if the dryer still needs two cycles after the visit, if the flap does not open on the test, or if you smell burning or see scorch marks on the wall or duct. In that case, turn the dryer off first and then make the call. Keep the written note with the appliance papers. Ask the company how often they think the vent should be cleaned for a household that runs its dryer as often as yours does, and write that date on the kitchen calendar so the next visit does not depend on anyone remembering.

Good-week card: One cycle, a warm breeze at the outside flap, and Dad telling you he always knew it was the vent.