Dryer vent combustible clearance?

[barlyhop]

I found this yesterday. Metal dryer vent ran through fiberglass flexible ceiling panel with no clearance. Ceiling panel was visibly distorted from heat.

I called for removing the ceiling panel in this area. What else would you say about this?

Thanks

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[Mike Lamb]

Dryer ducts have no clearance requirements from combustibles so I see nothing wrong here as far as the duct is concerned.

If the duct is over heating as you suspect, someone needs to seriously evaluate the dryer and the duct system.

[kurt]

I'd bet a dime the duct is clogged up and not functional.

Duct length varies wildly from mfg. to mfg. Go to the chart here, scroll down, and find your model.

As a basic rule, figure about 25'-27' max length, and take off about 5' for every 90 bend, although I've read deduct anywhere from 3' to 9' for a 90 bend.

If it's vertical, which yours is, you want to take reduce length considerably.

So, essentially, you don't want any duct longer than about 10'-12' if there's a bend in it anywhere, and there always are a couple.

Smooth walled only. No screws extending into the duct; tape the seams.

[Mike Lamb]

Don't use tape at seams unless it's easy to get to. Use hose clamps or rivets. As they say, duct tape works great on everything except ducts.

[hausdok]

Rivets would not be a good idea. The rivets will collect lint - that's why CPSC recommends using foil tape.

Dryer ducts get hot; that's a fact of life. That's why they don't recommend drying objects with rubber and plastic in the clothes dryer on the normal timed high heat setting. It could very well be clogged as Kurt said, or it might just have a few bends that are slowing down the air being pushed through it and making the metal hotter. Either way, I don't see some distorted plastic-faced ceiling panels with a hacked-through hole being a fire hazard. Heck the danged outlets are plastic half the time.

ONE TEAM - ONE FIGHT!!!

Mike

[kurt]

I'd never use standard duct tape, even for ducts. It's worthless for just about everything.

Gorilla duct tape doesn't let go. It's amazing. Or, foil tape. They both work.

[barlyhop]

Just above the ceiling, the metal pipe was connected to a heavy PVC pipe of the same diameter. The run had the one 90 there and then straight out through the wall about 8 feet.

Maybe it was condensation damage and not heat? The plastic coating on the ceiling tile just looked distorted.

Never saw a PVC pipe for a dryer run before.

Thanks to all!

Randy

[Marc]

A 114 unit condo complex where I once lived had underslab runs of PVC pipe for the dryer exhaust on about half of the units.. I derived a lot of service calls from that because the earth would cool the exhaust too much and the water which had evaporated from the clothes would condense inside the pipe, eventually filling it, since the pipe had to rise at both ends. I would vaccum them out and clean them. You could actually hear the gurgling sounds when the dryer was on. This was after I got my ears back and once I had learned the sound of gurgling water.

Marc

[Mike Lamb]

I'll have to try Gorilla tape.

[Brandon Whitmore]

Is gorilla tape listed/ allowed for that use?

[Chad Fabry]

PVC isn't allowed for dryer ducting. The ducting must be non-combustible.

[kurt]

Is gorilla tape listed/ allowed for that use?

I have no idea. I'm telling you though, I blanched at the thought of spending $12 for a roll of tape, but I have 3 rolls around the place now.

It actually does hold everything together. I've even "repaired" my canvas boat cover with the stuff.

It's still tape; it isn't going to hold an engine together. Just about everything else, though.

[Brandon Whitmore]

Hi Kurt,

I was smiling this morning when typing the question. I carry a roll of UL181 tape to use as an all purpose tape. It's amazing how much better the good stuff is. I won't waste my money on the silver stuff commonly known as "duct tape".

I think I paid 60-80 bucks per roll for the listed foil tape when I installed my heating system. 12 bucks seems like a steal for good tape.

[Bain]

PVC isn't allowed for dryer ducting. The ducting must be non-combustible.

I realize you're right, but it's used all the time here--in basements, slabs, crawlspaces. It's so pervasive I never call it a defect.

[hausdok]

It's kind of ironic that they say not to use PVC for dryer ducting yet they use PVC pipe for Category IV furnace vents.

ONE TEAM - ONE FIGHT!!!

Mike

[Brandon Whitmore]

It's kind of ironic that they say not to use PVC for dryer ducting yet they use PVC pipe for Category IV furnace vents.

Yeah, buttt.......

There's probably not any lint building up in a furnace vent, just waiting to be ignited. At least I hope not.

[Neal Lewis]

Brandon, you didn't mean $60-80 for the UL 181 foil tape , did you? I've bought even the 3 inch wide stuff for under $15. Helps keeps the asbestos on my steam pipes.

[pete moss]

In addition to being combustible, PVC should not be used for Dryer Vents due to static. Lint will accumulate within the piping at an accellerated rate.

[Brandon Whitmore]

Brandon, you didn't mean $60-80 for the UL 181 foil tape , did you? I've bought even the 3 inch wide stuff for under $15. Helps keeps the asbestos on my steam pipes.

Hi Neal,

Yep, that stuff. I set up an account at a local "wholesale" HVAC supply house, where their prices aren't posted. I placed the order, picked up the stuff, and then saw the bill.[:-bigeyes

The big box stores sell foil tape for 10-15 bucks that is UL listed, but it looks like cheapo stuff.

[lockem]

It is worth noting that PVC is not combustible. It melts at a low temperature, it burns when a flame is held to it (so will steel and aluminum), and when it burns it gives off extremely toxic fumes, but it will not sustain a flame on its own.

At least 1 website claims that the IRC requires a minimum of 28 gauge steel for dryer ducts. They did not quote the paragraph giving this requirement. I presume that any such requirement (if it exists) is there with the intent of containing small lint fires inside of the duct. 30 gauge steel seems to be the standard product to use, though. Does anyone know if this 28 gauge minimum is real?

My question is how much clearance is needed between an ABS DWV pipe and a dryer duct? I am concerned about overheating the ABS pipe and causing it to deform or melt. Without making the duct difficult to route, I end up with about 1 inch of clearance to the bottom of the washing machine standpipe P trap.

[Marc]

2006 IRC:

M1502.5 Duct Construction

Exhaust ducts shall be constructed of minimum 0.016 inch thick (0.4 mm) rigid metal ducts, having smooth.....

0.016 inch translates into 27 gauge.

Inch to gauge

Marc

[mjr6550]

Is gorilla tape listed/ allowed for that use?

I have no idea. I'm telling you though, I blanched at the thought of spending $12 for a roll of tape, but I have 3 rolls around the place now.

It actually does hold everything together. I've even "repaired" my canvas boat cover with the stuff.

It's still tape; it isn't going to hold an engine together. Just about everything else, though.

I had some small tears in my pool cover-the kind you can drive a car on. I thought $12 would be cheap if it worked, so I sprang for a roll. I'm about 3-1/2 months into the experiment and so far it is holding.

[kurt]

I've used the stuff to repair damp/icy canvas boat covers in the middle of winter; it worked.

[plummen]

It's kind of ironic that they say not to use PVC for dryer ducting yet they use PVC pipe for Category IV furnace vents.

Yeah, buttt.......

There's probably not any lint building up in a furnace vent, just waiting to be ignited. At least I hope not.

Theres not much of an issue with dryer lint building up and gluing itself to the inside of a heated piece of pvc on a furnace flue pipe.

[Mike Lamb]

It's kind of ironic that they say not to use PVC for dryer ducting yet they use PVC pipe for Category IV furnace vents.

Yeah, buttt.......

There's probably not any lint building up in a furnace vent, just waiting to be ignited. At least I hope not.

Theres not much of an issue with dryer lint building up and gluing itself to the inside of a heated piece of pvc on a furnace flue pipe.

You are probably right. "Yeah, butt.." as noted, code nor any clothes dryer manufacturer allows PVC. I do know clothes dryers are a fire hazard. I would mention in my report it's a no-no.