[jeffnc]

I'm looking at a dryer vent that passes through attic space over a garage to a side vent. The vent is rigid metal, approximately 20-25 feet long with one 90 angle at the dryer outlet. There are 3 rigid sections, followed by a short flexible duct section attached to the exterior vent. There is duct tape over the seams.

The problem is that water is dripping from the seams. Presumably this is because of condensation inside the duct in the cold weather we're having here in NC. There is no insulation. The duct run looks straight, but I don't know if there's a slope to to it. It's kind of hard to tell over the long run of it.

What is the best option here? Is it possible this could be solved by proper sloping and connecting the ductwork with overlapping connections in the right direction? Would it simply be best to vent straight up through the roof instead?

 

[TheEplumber]

I move this to HVAC. In my neck of the woods these pros install dryer vents- perhaps some one here will have some tips.

I'd start with insulating any vent in unconditioned space. Then replace the duct tape with foil tape- no screws on the joints.

 

[jeffnc]

Thanks for moving. Yeah good thoughts, but I don't think I want to rely on tape for waterproofing. Here are the pics by the way.

 

[TheEplumber]

Thanks for moving. Yeah good thoughts, but I don't think I want to rely on tape for waterproofing.

If it's insulated then you shouldn't have moisture. Are you sure there is not a leak at the exterior?

 

[jeffnc]

If it's insulated then you shouldn't have moisture. Are you sure there is not a leak at the exterior?

See new pics

 

[supers05]

Insulate the pipe. The problem will go away

Cheers!

 

[samjg1]

I found this thread in a search. I'm having the same issue.
The duct is going through a cold attic, and the condensation leaks at one of the taped joints.
In the meantime I've taped the joint using silicone tape:

http://www.homedepot.com/p/Nashua-T...sing-Silicone-Tape-in-Black-1208952/100206050

and monitoring it to see if it will stop the leak.

Is there a ready made insulation to put around the 4" duct?
Thanks!

 

[user_12345a]

Yes there is, you can buy it sometimes at a big box store.

I think it's fiberglass and gets wrapped.

If it's an exhaust fan vent it may be easier to just run insulated flex. You may need to use an adapter to increase the size to 5", as flex doesn't flow as much air at the same size.

Do not ever use flex for a dryer, the ridges can catch lint and pose a fire harzard.

 

[samjg1]

Yes there is, you can buy it sometimes at a big box store.

I think it's fiberglass and gets wrapped.

If it's an exhaust fan vent it may be easier to just run insulated flex. You may need to use an adapter to increase the size to 5", as flex doesn't flow as much air at the same size.

Do not ever use flex for a dryer, the ridges can catch lint and pose a fire harzard.

Thanks for the quick reply.
It is for a dryer duct, thus not using flex.
I will look for the fiberglass wrap.

 

[user_12345a]

http://www.homedepot.com/p/60-sq-ft-R-6-Insulated-Duct-Wrap-INSWRP60/100152008

 

[BayouRunner]

Insulating the pipe will work. It would be best to buy or rent a stapler for that purpose. But I think you will find there is a buildup of lint on the inside as well. Probably will need a good cleaning as well as insulating. What happens is the warm moist air going through the pipe in the cold attic causes condensation. Then the lint sticks to the inside of the pipe which aggravates the situation.

 

[samjg1]

http://www.homedepot.com/p/60-sq-ft-R-6-Insulated-Duct-Wrap-INSWRP60/100152008

That looks like it might work. Thanks!

 

[samjg1]

Insulating the pipe will work. It would be best to buy or rent a stapler for that purpose. But I think you will find there is a buildup of lint on the inside as well. Probably will need a good cleaning as well as insulating. What happens is the warm moist air going through the pipe in the cold attic causes condensation. Then the lint sticks to the inside of the pipe which aggravates the situation.

Thanks. Pardon my ignorance, but what would I need a stapler for?
Wouldn't the insulation just wrap around the duct?

 

[jlhaslip]

Canadian here. We run into this problem lots.

My technique is to use solid vent pipe that extends high as it enters the attic and slope it towards the exterior so any condensation gets drained away to the outside. Might require two of the adjustable 90's to get the right angle for the slope. Flex pipe will not drain condensation properly, so don't use it.

Yes, insulate the pipe as best you can. Tape will hold the insulation in place. Metal duct tape all joints before insulating.

Watch the direction of the pipe connections so that the condensation does not flow out at the joints. The male should be on the low end of the high pipe and insert into the female on the low pipe.

Same points apply to bathroom and kitchen vents.

Angling the pipe to rise early also reduces cold air from backflowing into the house. At least, to a degree. (see what I did there??? :lol: )

 

[SeniorSitizen]

That vent pipe needs a slope to drain because insulation will only make the internal pipe surface warm quicker than without insulation. The pipe will be at attic temperature when the dryer starts, the pipe will condense profusely and will not stop condensing until the clothes are nearly dry when the pipe surface can be warmed above dew point temperature. That DP temp. will be relative high as long as the clothes are the least little bit damp.

 

[BayouRunner]

You can use foil back tape to install it. I just like to use a stapler. The duct wrap doesn't come off when stapled. The tape works, just not as well.

 

[Gary in WA]

I'd use the foil tape rather than one that only sticks to itself... and meets Code in doing so. Cut the existing tape to remove/replace one section and after slipping some 6" flex duct over the metal pipe, tape all joints, including un-used elbows. http://www.homedepot.com/p/Master-F...le-Duct-R6-Silver-Jacket-F6IFD6X300/100396935

Tape (air seal) the plastic/insulation flex to prevent condensation. I'd be really surprised if you instantly had condensation when dryer first starts (or even during cycle) as it blows hot air first, after a few minutes- removes wet moisture that won't condense because metal pipe is already warmed and insulated against condensation and pipe is at dryer air temp, not outside temp, think pre-heating before the moisture comes through. Just MHO.

Gary

 

[BayouRunner]

Thanks. Pardon my ignorance, but what would I need a stapler for?
Wouldn't the insulation just wrap around the duct?[/QU
Yes the insulation wraps around the pipe, The staples hold the duct wrap in place. That's what we have always used. Its permanent