Need help with running new dryer vent

Old 07-24-16, 08:16 AM
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Need help with running new dryer vent

I need some help with modifying my dryer vent. It was originally vented out the back of my house. We had an addition put on, and the vent had to be rerouted. It now goes through my laundry room, into the garage attic, and to the outside. The run is 19' in total, but there are three 90 bends. My understanding is that the dryer vent cannot exceed 25', and you must subtract 5' for each 90 bend.

The vent seemed to work fine for the first 1.5 years. I've been having trouble with it for the last 12 months. We had the ducts cleaned 6 months ago, and the technician remarked about how much lint was removed. Yesterday, the dryer was not working properly, and I noticed there was no air flow out of the house. I took apart the ducts and removed a large amount of lint. It was very wet, and the galvanized steel was already rusty. What concerned me is that they installed semi-rigid ducting in the laundry room. I'm not sure why that was done. They also used screws instead of foil tape.

I would like to rerun the dryer duct, but I have some questions.

1. My understanding is that I have to use 26 gauge aluminum or galvanized steel. Is that correct? The existing duct work is only 30 gauge.

2. Would using aluminum prevent rusting? Is one better than the other? I've read that galvanized steel holds its shape better.

3. Would insulating the ducting that runs through the attic help with the moisture?

4. If I'm unable to remove the two 90 bends, would I need to add an inline fan?
Old 07-24-16, 09:23 AM
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Heavier gauge will be stronger and keep its shape better. I like to use 26 ga aluminum but it can be hard to find. Aluminum will not rust.

Running through attic space should be avoided if at all possible, but if it can't, insulating the duct with a minimum of 1" of fiberglass insulation will help prevent internal condensation.

Sheet metal screws should not be used as they trap lint.

Joints in the pipe should face away from the dryer, so there are no edges facing the airflow to trap lint.

A booster fan in your situation would be a good idea. It will increase the speed of the airflow, making lint less likely to drop out of the airstream, and giving less time for moisture to condense, and it will also reduce your drying times.

Seal all seams, both at joints and along the long seam in the pipe, with high quality foil tape. Getting the seams well sealed is especially important in the areas that will be insulated to avoid getting moist air in the insulation where it will condense and lead to wet insulation.

Avoid any kind of flexible pipe if possible. A short length to allow pulling out the dryer for cleaning or service may be necessary. If so, use the all metal flex tubing, not the spiral plastic type.

You may want to use Tees with covers on one leg instead of elbows as it will allow good access for cleaning the ductwork.

Support the run of ductwork enough so it remains straight with no dips or low spots to trap water. Ductwork is usually pitched back toward the dryer.
Old 07-24-16, 09:31 AM
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are you sure you can't reroute the vent? 19 feet with 3 ells is a lot. why can't you run it straight out the side instead of up and through the attic?
Old 07-24-16, 10:09 AM
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When the dryer is not against an outside wall a comprise must be made to get the vent line outside. Usually that means more fitting and longer lines.

Based on that you must add dryer vent clean out to your yearly maintenance items.
Leave access for future cleaning. Don't go crazy with the foil tape as some fittings will have to come apart again for cleaning.
Old 07-24-16, 11:31 AM
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are you sure you can't reroute the vent? 19 feet with 3 ells is a lot. why can't you run it straight out the side instead of up and through the attic?
I wish I could, but I don't think I have any other option. That's the closest run to the outside. My laundry room is situated in a way that it's a far run to the front, sides, or back. It used to vent to the back of the house, but with the addition, it's now a 29' run. The closest option was to run it up the wall, into the ceiling, through the attic, and to the outside.
Old 07-24-16, 12:36 PM
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CarbideTipped Said it well You may be able to reuse your old vents but take out all screws and use foil tape.NOT DUCT Tape Plan on a yearly clean schedule.
Old 07-24-16, 01:19 PM
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What's below the dryer room....can you run it down to a basement rather than up to an attic?
Duct should be pitched away from the dryer. Also, no pop rivets either.
Old 11-12-16, 05:02 PM
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Question Issue with Vent and Pipe to Attic

I have a house built in 1972. Our dryer is in the middle of the house and works fine. However, the vent goes out to a storage closet. In the storage closet there is a pipe that came off and broke some how. It won't fit on the duct crinkly pipe stuff my hubby bought and appears to long. Does anyone know what to do? The pipe that comes down from the attic is curved at the bottom and won't fit with the elbow thingy he bought or the crinkly pipe stuff attached to the dryer vent hole. Please help. We want to get this fixed so we can move on to other projects. Thanks.

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Old 11-12-16, 05:27 PM
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Melissa, it's hard for us to picture what you are describing. Is your picture in the storage closet? Does the elbow have a crimped end or non-crimped? Your pipe should really be solid pipe as it passes through that wall so that you don't gave to have flexible duct make a u-turn. I would suggest the solid pipe in your picture be turned around 180 degrees, then insert a 4" adapter (like this) through the wall, them put the flexible duct onto the adapter on the other side of that wall.

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