# Dryer duct: when 4" is not 4"



## Seabrook1983$ (Jun 19, 2019)

Making a new laundry room in an older house. Recently rented ($$$) a tool to bore a 4" hole through brick-over-block, 12-1/2" deep. All was well, nice smooth/clean hole which measures 4" in diameter.

Today decided to work on the duct and -- surprise, it's slightly oversize (4" is internal diameter, not outside?) I have two different brands of outside vent kit here, neither will fit.

OK, where do I get (a) 3-3/4" ducting, or (b) some tool (better than a chisel, this hole is deep) to open up the hole 1/8"?

Right now I'm faced with possibly trying to fabricate "undersized" ducting and closing the seam with pop-rivets, and then figuring out how to attach to the outside "cap".

Not sure if this is an "appliance", a "masonry" or "HVAC" question, I'll start at this sub-forum.


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## Bud9051 (Nov 11, 2015)

Hi Seabrook, I feel your pain. It is a learning experience and one you won't repeat soon.

Some of the masonry pros may have a thought on opening up the hole, I don't. My thoughts are similar to what you mentioned, creating a seam and reducing the diameter.

If you can find a 4.25" or 4.5" drill you could build a plug out of wood to fill the existing hold and help to keep the larger drill centered. Drilling a larger hole would be the neatest way to go, even if the new hole had to move a bit.

Bud


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## Nealtw (Jun 22, 2017)

Wrap the outside of your drill will gator grip. File some grit off the end so you can over lap it a bit.
https://www.equipdirect.com/BlackHeavyDutyGatorGripAnti-SlipTape36-Grit.aspx


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## Seabrook1983$ (Jun 19, 2019)

Thanks for input!



Bud9051 said:


> Hi Seabrook, I feel your pain. It is a learning experience and one you won't repeat soon. Some of the masonry pros may have a thought on opening up the hole, I don't. My thoughts are similar to what you mentioned, creating a seam and reducing the diameter. If you can find a 4.25" or 4.5" drill you could build a plug out of wood to fill the existing hold and help to keep the larger drill centered. Drilling a larger hole would be the neatest way to go, even if the new hole had to move a bit.



Thanks (A) while I know pipe is larger in physical size than the stated diameter, lumber is SMALLER than nominal size. Regardless... lesson learned. I figure zero chance of Home Depot renting me a 4.25" core bit. I could learn to make an undersized tube but wish me luck making a clean, secure transition to the outside "flapper" vent or, for that matter, the flex hose emitting from the dryer.



Nealtw said:


> Wrap the outside of your drill will gator grip. File some grit off the end so you can over lap it a bit.
> https://www.equipdirect.com/BlackHeavyDutyGatorGripAnti-SlipTape36-Grit.aspx


Interesting stuff. Can I make an 1/8" larger hole? I do not know, the cinder block (not concrete block) might yield but the brick is frightfully hard to cut or shape. The good news is that I do not need a large change. That said, the rental core bit, really deep, has been returned a while back -- but I also have a 4" diamond core bit that I bought years ago to attach to an angle grinder for cutting through a countertop... if I can figure out how to extend its' attachment to the grinder by a foot.


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## Druidia (Oct 9, 2011)

Hardware stores sell long strips of flexible galvanized sheet. They’re in the flashing stuff area. You can roll one up to make a 4” OD tube - insert into wall and end of vent duct. 

I learned never to trust stated measurements. Newbie/Ignorant me, years back, even whined to hardware stores employees why stuff can’t just be labeled with actual measurements instead of “estimates”. 

Especially when buying online - too frequently, there’s just one diameter stated. So, have to ask sellers - is that OD or ID?


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## Nealtw (Jun 22, 2017)

Could check with a muffler shop and see if they have a 4" OD pipe,


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## SPS-1 (Oct 21, 2008)

I expect you could rent a "die grinder". Its going to be slow work, but that might do it. Anything you can chip out with a chisel will be less work than grinding it away.


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## huesmann (Aug 18, 2011)

Druidia said:


> Hardware stores sell long strips of flexible galvanized sheet. They’re in the flashing stuff area. You can roll one up to make a 4” OD tube - insert into wall and end of vent duct.


Yup, something like this: https://www.homedepot.com/p/Amerima...Aluminum-Roll-Valley-Flashing-68310/100054269

Roll your own. Pun intended.


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## Colbyt (Jan 27, 2014)

A lot of people use 3" PVC for the dryer duct. I've done it. It works just fine with the flapper and the hose secure to the pipe just fine with the proper clamp. It stays cleaner.


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## Seabrook1983$ (Jun 19, 2019)

Druidia said:


> Hardware stores sell long strips of flexible galvanized sheet. They’re in the flashing stuff area.


Gotcha. Was planning on just buying a length of larger, say 6", duct as raw material.



Nealtw said:


> Could check with a muffler shop and see if they have a 4" OD pipe,


Clever answer -- IF the 4" is indeed OD. Never thought about that before.



SPS-1 said:


> I expect you could rent a "die grinder". Its going to be slow work, but that might do it. Anything you can chip out with a chisel will be less work than grinding it away.


Which would work, although the very solution I'm trying to avoid, mostly due to the depth of the hole.



huesmann said:


> Roll your own. Pun intended.


Probably not with a pretty seam like the commercial stuff, but with a series of rivets.



Colbyt said:


> A lot of people use 3" PVC for the dryer duct. I've done it. It works just fine with the flapper and the hose secure to the pipe just fine with the proper clamp. It stays cleaner.


BRILLIANT! Tell me more about how to attach the flapper outside, and the fleet line from the dryer inside.


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## Colbyt (Jan 27, 2014)

> BRILLIANT! Tell me more about how to attach the flapper outside, and the fleet line from the dryer inside.



The pipe must be well secured to the home framing and it just butts against the vent base. After bad experiences I only use the all metal version of this https://www.homedepot.com/p/GE-4-in-Dryer-Vent-Kit-with-Hood-PM8X85DS/202049948 The pipe can be removed and metal tape can be used the connect the lip on the vent to the pipe. I actually don't but you could.


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## Seabrook1983$ (Jun 19, 2019)

Colbyt said:


> The pipe must be well secured to the home framing and it just butts against the vent base. After bad experiences I only use the all metal version


I have here both a metal flapper similar to that, plus a plastic multi-vane vent. I'll visit Big Orange for some of that pipe, and scan the aisle seeing if they stock a "flange" in that size, which would facilitate attaching the flapper. Not yet sure how I "transition" from the 3" pipe to the 4" flex line to the dryer yet. Also need to determine how to secure the pipe to the wall, which is the masonry and the interior just has furring strips to hold the drywall.


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## CodeMatters (Aug 16, 2017)

I'd make the hole the right size. 
Take a piece of plywood something like 1' x 1'. 
Find the right size coring bit (possibly 4 1/8"). 
Cut a circ hole in the plywood same size as the coring bit.
Screw the plywood to the inside or outside of the wall centered
over the existing hole. 
The plywood will act as guide to allow re-coring the wall hole. 

Whenever I've tried to make due with an incorrect starting point 
I've regretted it as the complications cascaded.


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## Seabrook1983$ (Jun 19, 2019)

CodeMatters said:


> Take a piece of plywood something like 1' x 1'.
> Find the right size coring bit (possibly 4 1/8").
> Cut a circ hole in the plywood same size as the coring bit.
> Screw the plywood to the inside or outside of the wall centered
> ...


This is exactly what I did for the first hole; I made a guide and it worked great. Alas, the only size bit that Home Depot had for the rental was 4". I've looked on-line and do not want to spent $239.99 to buy a 4-1/4" x 14" bit (and still have to rent the drill again).


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## rjniles (Feb 5, 2007)

I had the same issue years ago. My cheap solution was to use a sawsall to cut 1/4" slots every half inch around the existing hole. Knock the pieces with a chisel working from both sides. Only took half an hour.

Sent from my RCT6213W22 using Tapatalk


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## Seabrook1983$ (Jun 19, 2019)

Colbyt said:


> A lot of people use 3" PVC for the dryer duct.


Just back from Home Depot with a length of 3" pipe. Nosing around the department looking for a way to attach at both ends, I stumbled upon: toilet flanges! I picked up two "PVC Open Flanges" where the mounting collar goes outside the pipe, not inside; no restriction. The exterior flange, which I'll trim to fit aesthetically, allows attaching to the brick exterior (blue screws?) and the flapper (RivNuts on the flange allowing machine screws?) I'll pass the pipe all the way through the interior flange, so it sticks out (in?) and bought a connecting collar for 3" pipe -- the exterior of that , like the toilet flange collar, is 4" so it's not only a great fit in the bored hole in the wall, but I now have a place to attach the 4" fleet line from the dryer.



rjniles said:


> I had the same issue years ago. My cheap solution was to use a sawsall to cut 1/4" slots every half inch around the existing hole. Knock the pieces with a chisel working from both sides. Only took half an hour.


Were it only the block, and not the brick, I'd be all over this. As it is, that's "Plan B" if the PVC does not work out.


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## Seabrook1983$ (Jun 19, 2019)

Colbyt said:


> A lot of people use 3" PVC for the dryer duct.


I was asked yesterday about heat when using PVC pipe. Is it know (a) what the melting point of PVC pipe is, and (b) average dryer outflow air temperature?


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## Seabrook1983$ (Jun 19, 2019)

BTW, a quick Goggle search results in:

Traditional product PVC has a maximum operating temperature around 140°F (60°C) when heat distortion begins to occur. Melting temperatures range from 212°F to 500°F (100°C to 260°C) depending upon manufacture additives to the PVC.

How hot should a dryer exhaust be?
The exhaust temperature of a dryer typically cycles from 50 to 71°C (120 to 160°F), though there is a potential if the dryer is broken it could be higher (any dryer made since the 1980's has a thermal fuse in it, hard to find info but it sounds like these often blow at 198 or 185°F)

What is the temperature inside a clothes dryer?
The temperature inside a clothes dryer varies depending on the setting; low heat is approximately 125 degrees Fahrenheit, while medium heat and high heat are approximately 135 degrees Fahrenheit, according to GE. But the temperature is affected by several factors.


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## SPS-1 (Oct 21, 2008)

When I did a search for any relevant code I found an IRC-2015 line that duct will be metal. 
https://codes.iccsafe.org/content/IRC2015/chapter-15-exhaust-systems 

However, Ontario Building Code (where I live) only says smooth, corrosion resistant material. So likely depends on where you live.


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## Colbyt (Jan 27, 2014)

A lot of people use plastic vent duct which has to have a lower melting point.


It is used by builders here.


90% gas furnaces are vented using 2" PVC pipe.


Don't let me talk you into it. Make your own judgement call.


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## Nealtw (Jun 22, 2017)

I found a metal tube that is just under 4 inch diameter and just under 9 inches long. 

https://www.walmart.ca/en/ip/nescaf-rich-instant-coffee/6000145830534


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## Seabrook1983$ (Jun 19, 2019)

I'm getting good input here! Thanks!



Colbyt said:


> A lot of people use plastic vent duct which has to have a lower melting point. It is used by builders here. 90% gas furnaces are vented using 2" PVC pipe. Don't let me talk you into it. Make your own judgement call.


I had not thought of that; our, eh, 8 year old boiler is vented through the wall w/plastic pipe, leaving the ($$$) stainless-lined chimney unused now.

Was thinking of drilling a tiny hole once done, inserting my remote-read BBQ thermometer's prob in the hole and testing the resulting temp.



Nealtw said:


> I found a metal tube that is just under 4 inch diameter and just under 9 inches long. [/url]


:biggrin2: That's funny! :biggrin2:


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## Nealtw (Jun 22, 2017)

Seabrook1983$ said:


> I'm getting good input here! Thanks!
> 
> 
> 
> ...


How many people get a way with that junk plastic flexible duct right off the back of the dryer.


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## Colbyt (Jan 27, 2014)

Nealtw said:


> How many people get a way with that junk plastic flexible duct right off the back of the dryer.



Me for one for 23 years now with a gas dyer. Very short run, very hard place to work, absolutely no room. And I had it all exposed 6 months ago when I replaced the washer fill valve.


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## Seabrook1983$ (Jun 19, 2019)

I like how it's turning out. Both flanges needed trimming to fit -- the inside one to clear a firring strip, the outside one to not project beyond the flapper (which sits away from the brick by the thickness of the toilet flange, so I'll need caulk/whatever). Sit have not determined how much of the pipe sticking into the room (about a foot now) gets chopped off.

I want to say thanks for all of the input; one tends to get a lot of counterproductive "help" when asking for advice on the internet. Not this time.


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