Can't find rigid, smooth ducting?

[qbert]

What do people use for 6" & 8" round rigid ducting?


The only PVC I can really find in Home Depot, etc. is 4". They have 6" but it is really thick walled and EXPENSIVE. They don't carry 8" PVC at all. I also saw the metal ducting - again only in 6" - but this stuff looks like a nightmare to deal with: sharp edges, crimped seams needing massive amounts of tape, etc.


So, what do you folks use and where do you get it?

 

[cashmunny]

Is this for an air cooled hood or for water?

I think most people use dryer exhaust tubing for air cooled hoods.

You could buy thin walled aluminum tubing from someplace like McMasterCarr.com I suppose. Don't know how you would handle joints and elbows.

Maybe stove pipe? Like the kind for pot bellied stoves? I imagine they make elbows and fittings for that.

 

[qbert]

Actually, Menards had insulated flexible ducting in 6" & 8" - but the insulation, which is un-needed, makes the overall duct diameter FAR too large to be usable. Also, the insides of this ducting did not seem very smooth. I am looking for something smooth like PVC to maximize my airflow efficiency. I would guess plastic flex tubing (not really sure what this is, different from the wire & mylar flexible ducting?) would also not have a smooth interior surface.

 

[Xero000]

Don't know where you're located, but this looks like what you want.

They'll also have elbows, tees, and caps as you need them. The stuff really isn't that bad to work - a screw gun (cordless drill), a roll of good tape and some hanging strap is all you need. Make sure to use self tapping hex-drive screws to make it easy on yourself. The crimped ends are what makes it easy to connect your pieces together - it's a good thing, not bad.

You'll still need to use some flex duct to connect to your lights so they can be moved & positioned.

Good luck.

 

[xcrispi]

Like Xero said man . Ditto him .

You might have to go to a HVAC type place for larger than 6 in though .
I found 8in and 10in here local by me , and def splurge and buy the sweet aluminum backed duct tape - it rocks .
Crispi

 

[qbert]

^ yeah, that's the sheet metal stuff I can find locally (but not in 8").

I don't see cabinets with in-built scrubber/fan using this stuff. It's like everyone uses flex or insulated flex even though everyone says flex is terrible for efficient air flow.

After handling those elbows in the store, I don't know that I could ever make them air-leak-proof, short of submerging them in an epoxy or something. They are made of like 5 separate metal pieces riveted together - each piece is able to rotate to create different angles so there's a lot of seams to seal.

 

[Ms_Weekend]

to seal them you have to use duct mastic & mesh tape.....one coat will work on the outsides.....or you could use alum. tape, but the mastic and mesh tape is far easier & cheaper when you get the hang of it

 

[qbert]

to seal them you have to use duct mastic & mesh tape.....one coat will work on the outsides.....or you could use alum. tape, but the mastic and mesh tape is far easier & cheaper when you get the hang of it

ok, well I guess I should give it a shot with so many quick responses saying this is the stuff to use.

 

[Lazyman]

I get up to 12" rigid sheetmetal ducting at Home Depot, and no you cannot use PVC, it's stupid expensive and very heavy. It also isn't designed to fit ductwork like sheetmetal is.

 

[qbert]

it's stupid expensive

werd. when I finally found some fair lengths of even just 6" I was like

 

[Xero000]

I don't have any scientific studies to back this up, but I believe you're not going to see a terrible difference in efficiency between flex duct & round pipe at the velocities and distances you're likely trying to push air across.

It would be one thing if we were comparing the laminar flow of air through a straight run of round pipe to the more turbulent flow inside a flex duct. But there will be plenty of sources of turbulence even in a round piped system including the sections of flex, ells & turns, and flowing through multiple lights (if that is the configuration). My point is there will still be turbulent bottlenecks that will serve as rate limiting factor, even with the pipe. Plus, I really don't think we're going to be pumping air fast enough to make a noticeable difference.

 

[growclean]

I get up to 12" rigid sheetmetal ducting at Home Depot, and no you cannot use PVC, it's stupid expensive and very heavy. It also isn't designed to fit ductwork like sheetmetal is.

We had trouble finding what we wanted at Lowes and Home Depot. After a third local hardware store, we finally connected with a commercial hvac supply store. They sold us everything even though they technically weren't supposed to. We just explained that we were doing it ourselves and couldn't find all the parts anywhere else. It was pretty easy and now that we established a relationship with one of the guys, we can probably go back and get whatever we need.

 

[Randybobandy]

Sounds like you want to make it perfect. I once heard that perfection is the lowest standerd because it can never be acheived. Kudos for the vision but strait duct won't get you more doobies. If you spent the funds else where it would help more. But if you got money to burn or your setting up a type of "show" room fuck it go all out. If your limited on funds allocate the capitol towards gear that produces more results. You might even save money by buying regular duct work and getting a bigger fan(s).
When i first did rooms I wanted everything to look/seem pefect. I learned to get em up and running with no more than I needed. Saved time and money. Just make sure your ducting dosent have to many 90's. See lots of guys killing the flow. Good luck dude. Get that room going!

 

[qbert]

^ I hear ya man. I definitely lean towards the perfection end and have some serious obsessive-compulsive tendancies (not quite disorder level, but yeah ..)


My biggest BY FAR concern is stealth. With fans its noise. Maximizing efficiency means dialing my already large fan down a little more means less mechanical fan noise, air speed noise, and air turbulence noise. This is going to be an armoir in a bedroom in an apt exhausting back into the room, so its definitely a concern.

This one aspect seems important enough to spend some time sorting out. But on the other hand, if I wouldn't have spent all this time finding what I felt to be the best piece for every last little stinkin detail I'd already be nearing in on chopping crop #1, instead I'm still a month or more away from sprouting crop #1.


After this thread I think I'm just going to try some flex duct and see how it does. I had to buy 25' of 6" flex duct anyway for the movable hood. It also gives me a chance to try a single fan pulling through filter and hood rather than separately exhausted hood. And 1 fan vs. 2 should be a significant drop in generated noise inside the cab.

 

[PharmaCan]

qbert - If you are going to go with flex duct, I'd suggest getting the insulated flex duct that they use for hvac work. The insulated duct is not only quieter, but stronger too. I've had even the good quality dryer-vent-type, shiny silver, single wall flex duct fail. The insulated duct is available at Lowe's, Home dePot, etc.

If you want to get rigid duct or rigid fittings, look in the Yellow Pages for "sheet metal" shops or fabricators in your area. They usually have a good variety of fittings and sizes for reasonable prices.

I've often wondered about some of these supply stores that will only sell to contractors/companies. The only thing that really makes any sense is that they don't collect sales tax and only sell to resellers. If you think about it, jumping through all the sales tax hoops can be a significant expense and maybe these companies have just decided to completely eliminate that expense, and the hassle, of dealing with sales tax.

PC

 

[Randybobandy]

A large fan on half speed cuts noise sooo much. Go bigger ducting with slower flow. Rehostats(speed contolers) and insulated ducting like Pharma said. Most of the noise comes from turbulance. Corners and high velocity.