Dryer vent max length?

[iafirebuff]

Hello. I am thinking of moving my dryer vent and was wondering, what is the maximum length you can go with a metal dryer vent? (the accordian type - metal foil like with a "slinky" like skelton - flexible).

Here is the deal - our dryer vent vents out to within about 2-3' of our outside AC Compressor. I have notice that lint gets caught in the fins of the A/C. So I would like to move the vent/duct to the other side of our house. I always clean the duct once a year and I replace it every 2 years. When our house was set up, they used PLASTIC vent - (back in 92), I replaced it with the flexible metal/foil fire retardant type years ago, and like I said I keep it clean/new.


So to my question - as it is now there is approx 8-9' of dryer duct with 2 bends. I would like to vent it to the other side of our house, which would be about a 12-13' run with only one bend where it comes out under the house then a straight shot. Does anyone know should I be ok with about 13' of duct work? THANKS in advance!

[JD]

You may want to change your ducting to rigid metal duct. Code for smooth wall dryer ducting, 4", is 25', although that is much more length than I would feel comfortable with. If you check it frequently for clogs and build up, it probably would be fine, but most people don't do that. Sounds like you would. The better quality flexible ducting is much smoother walled than the cheap stuff, but it would still tend to develop bellies and waves in it. I don't know if they are considered "smooth wall" ducting, but if they aren't the maximum length should be written on the packaging.

Rigid pipe is easy to work with and is practically rodent proof. Instead of replacing it every couple of years, you could disconnect it at the bend going up to the dryer and clean it out with a duct brush (also fairly inexpensive). Could save you money in the long run.

Also, the 25' length is for a straight pipe. You deduct 5' for every 90 degree bend. International Mechanical Code article 504.6

JD

[iafirebuff]

THANKS for the info! I have been using the higher quality "smooth" walled flex duct. It is pulled tight and rigid (as can be) when I am done. I thought about the pipe.....I am not sure how I would support it though.

[JD]

They make a pipe hanger for this pipe, but I would opt for regular plumbers tape (the metal strap with holes in it) and form it real well. I would also wrap it with electricians tape or something non-conductive to prevent premature rusting. I would also wrap it in the middle of the pipes and not the joints. The rigid pipe usually comes in 2' sections and there are short extensions to make the length come out right. I would tape all joints with vent pipe tape to make sure it all stays together.

I would imagine that the quality aluminum flex pipe should work for this distance you need, but be sure to read the manufacturer's instructions.

JD

[iafirebuff]

THANKS again for the info! In case others are reading this, I always use the metal tape (not sure what it is called) - not "duck" tape. THe metal tape holds up so much better!

[Yanita]

Hi,

I am with JD on the hard pipe, much better than anything flexible. Also with hard pipe no more than 2 ells.

Yanita

[bell30655]

My last house (no wheels under it) when it was built encountered a problem. The code here says 25' for dryer vent is max and every bend counts as 5'. Since I was wanting the laundry room in the center of the house, I could not reach any outside wall within the requirements.

I wound up with one 90 degree bend and then straight up out the roof. Met the requirements.

On the rigid pipe versus the flex hose, I agree 100%. One of the first things that I had to replace was the flex hose because a cat was trying to get into the warm hose.

[Robert]

Hi Larry,


Go with smooth walled aluminum pipe, very light so support issues are minmal and no rusting as you have with galv. hard vent pipe.


The foil tape is duct tape, just a much better type.


Run it the shortest length possible with fewest ells.



Thanks,
Robert