Project math question

[Tunnelcat]

I'm not a math whiz so I need a solution for this project I'm doing. Foil? I want to install a new dryer vent inside a 3 1/2" by 16" stud wall behind my dryer. I've got a 4" diameter round dryer duct presently, which hangs from the ceiling and is really butt ugly. I'd like to know the equivalent area, or in other words, the width I need for a rectangular duct that can only be 3 inches deep in the other dimension. I want to have a rectangular metal duct made by my local HVAC company, then cut a hole in the wall's top plate in the attic and slide it down inside the wall.

[Foil]

I'm having trouble visualizing what you're looking for...

Are you wanting to equalize the cross-sectional area of the duct, as follows?

Area of rect duct = Area of round duct
=>
3" by x" rectangular = 4" diameter round
=>
3x = Pi * (2)^2
=>
3x = 4Pi
=>
x = ( 4 / 3 ) * Pi ~= 4.19"

If that's not it, I need some clarification.

[Spidey]

Personally I would just go with 3x6 because of the change in flow characteristics, and wouldn’t really worry about an exact equivalent. (area wise)

Unless of course you want it as small as possible.

[Tunnelcat]

Yeah, I'd like to get an equivalent cross-sectional area Foil, preferably slightly larger, since a rectangular tube isn't as flow efficient as a circular tube. I do have room for up to 12 inches wide Spidey, but I'd like to keep it as small as possible without sacrificing flow rates. I don't want to have to take out any electrical boxes or too much of the top plate either. It does hold the drywall edge up there.

[Spidey]

I’m going to assume you are going to adapt back to 4” round at both ends of this duct?

If that is the case, I would look into what standard 4” round adaptors are available, and take some of my clues from that, unless of course you are going to have custom adapters made as well. $$$$$$$

And I am going to assume you will need right angle adapters? In that case I doubt you will find a 4” round to 4.2” square. (but you never know)

I’m pretty sure you will need the width to be a standard size, unless you plan to go all custom.

At any rate…take your clues from the type of adapter you will need, then go from there.

[Krom]

Yeah, what Spidey said, look at some dryer vent adapters. IIRC some I've seen were something like 2 inches by 6 inches rectangular and made up of sheet metal.

Edit, something like this: http://www.newegg.com/Product/Product.a ... 6803005339

[Isaac]

You don't need a calculator, TC. What you need is



if space < dryer: walls+sledgehammer

[Tunnelcat]

I’m going to assume you are going to adapt back to 4” round at both ends of this duct?

If that is the case, I would look into what standard 4” round adaptors are available, and take some of my clues from that, unless of course you are going to have custom adapters made as well. $$$$$$$

And I am going to assume you will need right angle adapters? In that case I doubt you will find a 4” round to 4.2” square. (but you never know)

I’m pretty sure you will need the width to be a standard size, unless you plan to go all custom.

At any rate…take your clues from the type of adapter you will need, then go from there.

Yeah, I have to adapt to the dryer and outside vent pipe which are 4" in diameter as well, so that's the idea. It's not the adapter that's the problem, but the part inside the wall that has to be made rectangular to fit the space. 3" round pipe is not sufficient airflow. So your 3X6 rectangle idea sounds about right.

if space < dryer: walls+sledgehammer

Well duh! But I'm lazy and I don't want to have to rebuild the whole damn wall. I HATE doing drywall! If we'd been a little wiser when we had the house built, we would have had a 2"X6" stud wall built in the laundry room, which we had the room for and which would have allowed for a 4" round pipe in the first place. But noooooooooooo, that would've been too easy and taken some forethought. [slaps face with palm].