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Dryer Venting - in 2x4 studs

Posted by oldbat2be (My Page) on
Sun, Aug 21, 11 at 14:37

In our remodel process, we need to vent a dryer up through an interior 2x4 wall, 16 on center, up through the ceiling.

Upstairs is attic space, we will vent from here to the outside.

Does anyone know what we need to transition from the 4" round dryer exhaust, via the 2x4 wall? We've checked Home Depot and Lowes and cannot seem to find the correct transition pieces.

Thanks in advance!


Follow-Up Postings:

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RE: Dryer Venting - in 2x4 studs

We just went through this, and lost 2 (more) inches on the laundry room. Builder told us we needed 6" walls to vent, so they added 2 more inches to the interior wall.

(the person who drew our plans on CAD was an idiot, and should be banned from the industry)

Good luck! Hope someone gives you good information.


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RE: Dryer Venting - in 2x4 studs

As the poster above points out, it won't fit. Remember a 2x4 is actually 1.5"x3.5".

A 4" 90 degree would normally do the job for the vent. If the big boxes don't have that, look for a speciality HVAC supplier.


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RE: Dryer Venting - in 2x4 studs

Also keep in mind an access to periodically clean out the ducting. I would run this by a reputable hvac outfit in your area.


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RE: Dryer Venting - in 2x4 studs

Does a dryer vent have to be round? Perhaps your HVAC sub has a suggestion or two for what an appropriate duct might look like that fits within your joist space.


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RE: Dryer Venting - in 2x4 studs

Try the Dryerbox Model 350. I used this downward version of this into my floor and transitioned to an elbox. You should be able to deform a 4inch duct into the oval shape. If you poke around the website they may have some more ideas about venting into a 2x4 wall.

Here is a link that might be useful: DryerBox


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RE: Dryer Venting - in 2x4 studs

You can try and squeeze a 4 inch duct slightly out of round and fit it in a 3.5 inch space.

It gets a little hard when you need to distort a bend but it can usually be done.

Square ducts tend to collect more debris on the corners, one of the reasons they are not usually recommended for dryers.

Making the duct excessively large can also drop the flow speed enough lint will fall out of ht airstream and collect.

A 3.5 x 14.4 square duct would be excessively large.


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RE: Dryer Venting - in 2x4 studs

Dryer ducts collect a lot of lint and are a big source of house fires every year. It is a VERY BAD DESIGN to try to vent them upwards through a roof, or downwards through a slab. I don't know when this bad design became common, but just because it's done doesn't mean it should be. Laundry rooms should be located on an exterior wall where the ventilation can be directly out that wall with the shortest possible vent. Your fire department will thank you.


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RE: Dryer Venting - in 2x4 studs

It is a VERY BAD DESIGN to try to vent them upwards through a roof, or downwards through a slab.

Am I embarrassed I didn't pick up on this point! Every couple of years I vacuum out our dryer line and there's an amazing amount of dangerous lint. And that's on a straight run out the first floor. Fifteen thousand dryer fires a year in the US.

Here is a link that might be useful: Dryer Fires


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RE: Dryer Venting - in 2x4 studs

"Fifteen thousand dryer fires a year in the US."

Sounds ominous.

How many dryers are there?


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RE: Dryer Venting - in 2x4 studs

If possible, the op would be better off running a chase along the floor and out an exterior wall. The run they have planned is way too long running up and lint will most likely collect at the elbow in the attic as there wont be enough pressure from the dryer to push it up and out. Short, straight runs with hard ducting are always safer. Flex ducting is risky as well. In any event, ducting should be cleaned out every six months. Longer runs with turns should be cleaned out more often than that.


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forgot to mention

A friend had one of these. Worked okay but seems like a pita. Something to consider though.

Here is a link that might be useful: indoor dryer vent


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RE: Dryer Venting - in 2x4 studs

At least 87.5 million in household use. Plus those in laundromats, government institutions, medical facilities and commercial establishments. Think of the energy (and lives) we'd save by banning them!

Before Dryers


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RE: Dryer Venting - in 2x4 studs

"Flex ducting is risky as well."

Under most building codes a single length of flex ducting (limited to about 8-10 feet) is allowed from the metal duct to the dryer outlet and it may not be enclosed in the wall.

"At least 87.5 million in household use."

So 0.017% of dryers cause a fire every year.

Sounds like very good odds, and not a very significant problem at all.

Remember the old thing about X% of accidents are withing Y miles of home?

Ever wondered what percentage of all driving is within Y miles of home?
Notice no one actually gives you enough information to actually evaluate the risk?


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RE: Dryer Venting - in 2x4 studs

To the OP: IRC Code advises that the vent should not be more than 25' from the appliance and that any 90 degree bend reduces that length by 5 feet.

Sounds like very good odds, and not a very significant problem at all.

I have a sneaking suspicion that the odds are rather higher for installations that violate regulations on types of venting to use and that are never cleaned.


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RE: Dryer Venting - in 2x4 studs

"Under most building codes a single length of flex ducting (limited to about 8-10 feet) is allowed from the metal duct to the dryer outlet and it may not be enclosed in the wall".

Which is fine except when you see them installed improperly resembling a twisted pretzel or snake......not good.

If the op installs it in the wall cavatie stud space, how will they treat the broken/cut top plates? I'm sure simpson has a code correct strapping?


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RE: Dryer Venting - in 2x4 studs

If you look at the item I posted (DryerBox) it significantly helps with the squashed flex line problem. You transition to 4" hardline at the Dryerbox and sent it up the wall as an oval not a circle. (On a 2x6 wall it stays round) Once the oval passes the top plate the round duct goes back to round if you give it a foot or so of run. You want it round before you do a 90 if necessary and they sell a swept 90 that negates the five foot penalty.

Of course none of this negates the need to clean but if you can't or won't put the dryer on an exterior wall this is an option.

Here is a link that might be useful: Long Turn Ell


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RE: Dryer Venting - in 2x4 studs

"they sell a swept 90 that negates the five foot penalty. "

It may reduce it to less than 5 feet, but it cannot eliminate it.

Turns are always more than the length of th eturn, how many times the actual length can be reduced closer to 1.0, but it never gets there.

"To the OP: IRC Code advises that the vent should not be more than 25' from the appliance"

And like any other code provision the installation instructions that came with the equipment tale precedence.


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RE: Dryer Venting - in 2x4 studs

Brickeyee states "It may reduce it to less than 5 feet, but it cannot eliminate it.

You may not think so but the mathematics do not agree with you. At least according to the calculations provided in the link... I didn't double check them as I am a trusting sort.

For the purposes of the OP the DryerBox product (which I merely point out as a solution to a design challenge) will allow venting though a 2x4 wall and if they need to make a 90 degree turn that swept ell might provide a solution.

Here is a link that might be useful: ASHRAE Calculations


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RE: Dryer Venting - in 2x4 studs

One of the other casualties of the idiocy of up or down venting is the dryer itself. I can't tell you how many people go shopping for a new dryer 2-3 years after they replaced the old one. When you get blocked airflow, you burn out elements. And lots of people don't have a clue as to how to replace an element or clean a duct out. So they just buy a new one and wonder why it still takes 2 hours to dry a load in their new dryer.

There used to be several threads on the Laundry Forum showing pics of how badly lint accumulates in such a duct. It IS shocking. I did find a thread that showed how much lint was pulled out of a simple direct to the exterior vent. Something through the roof would have 10 times as much possible lint accumulation. Think about it!

Here is a link that might be useful: Lint pics


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RE: Dryer Venting - in 2x4 studs

"You may not think so but the mathematics do not agree with you."

All models are wrong, some models are useful.

ANY turn in a flow increases drag.

That is sort of fluid flow 101.

If they are saying otherwise I would not trust anything else they claim.


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