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Kiln Exhaust Ducts

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The flexible duct that connects my electric kiln to the exhaust system (and from there outside) keeps cracking. So far I have been patching it with aluminum tape, but I'd like to replace the duct itself. Is it safe to use a replacement duct from Home Depot designed for clothing dryers? If not, what is safe to use? I fire the kiln to 2400 degrees, but I don't know how hot the duct will get.

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If you need flex go with more flex which is aluminum-the only tape I know that would hold up is that silver aluminum tape that has a paper backing for heat duct work.Make sure the flex has no plastic in it.Big box stores usually have very poor selection of duct work.

If you can use metal solid duct as it will hold up better or a small length of flex than solid which can be screwed then taped-that duct comes in single wall 3 , 4 ,5 or 6 inch aluminum or mild steel or galvo (avoid) which will put of bad fumes- sold at heating supply stores.

Mark

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The primary issue with the ductwork for a downdraft vent is not necessarily the heat. Because the vent pulls so much room air compared to kiln air, the temperature of the air in the duct will be under 150 degrees. The fumes and moisture from the kiln, however, will corrode the vent. Take a look at the inside of your old vent- it will be coated with tons of crud. Do not use the clothes dryer type ducts, as they are too thin and flimsy to hold up for very long. Go to the duct section of Home Depot (or Ace, etc.) and get semi-rigid (flexible) duct. It will cost you $10- $20.

 

They are now also making plastic ducts that hold up to the corrosion much better than the metal ducts, and can withstand the 150 degrees as well. They are costly, though, by comparison. Check out McMaster-Carr if you're interested, I think they have them.

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The flexible aluminum dryer vent product at the box stores works well.

 

If anyone is interested I would be glad to post some pics of the DIY vent system I made for my used Skutt after looking at what they (and other manufacturers) sell for over $400.

 

good luck, all

 

teardrop

Joseph F likes this

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I recently installed a new exhaust system for two kilns it only came with enough aluminum duct for one, we found the same duct at a box store (Menards) for 12 dollars. My husband said it was the same material, Skutt had the extra duct for 40.00 plus freight if it makes you feel better ordering it from them. I'm lucky I have a live in expert my, husband writes books on maintaining and operating anything from airplanes to amusement rides, last week he was teaching new techs how to install a two story carousel. Denice

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Do not use plastic dryer type ducts as they off gas and degrade. Go to Home Depot or Menards and you can get whatever you need. I agree with Mark that you should have a solid section attached to the wall. Alo make it longer than you need so that it loops down to form a heat sink. Just a loop of tubing, then you have less cold air coming into your space, or less warm air leaving. I am building mine as well, so have been thinking about this. The condensation happens when cold outside air hits the warm vent gases, and rusts your pipe. Galvanized is also not good as you get fumes.

TJR.

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The flexible aluminum dryer vent product at the box stores works well.

 

If anyone is interested I would be glad to post some pics of the DIY vent system I made for my used Skutt after looking at what they (and other manufacturers) sell for over $400.

 

good luck, all

 

teardrop

 

 

I would be interested in seeing what you did.

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OK....here we go:

 

Preface: I bought a barely used Skutt 818 in Denver for a song. It had a stand but no vent system. I immediately found the EnviroVent install manual/product info online and started digesting it/trying to see how/what was required/etc...

 

Without a vent the bottom of my kiln is bare brick. The stand...being angled steel stock....contacted the brick and could easily cause damage/wear so I knew I needed to protect it. Fortunately the kiln had only been moved once before I moved it and was owned by the person who originally bought it.

 

It appeared to me that the stock vent system was made of sheet metal but I not only don't have decent access to such material I've also worked with it enough as a machinist to know that it is a pain/can easily cut you/etc. without the proper tools/gear....so I started looking for a cost effective/easily sourceable alternative.

 

what I came up with is 1/4" thick "hardi-backer board" that is used to strengthen floors/shower stal walls/etc. so they can accept tile. Easily sourced at Home Depot/etc....it is non-flammable....relatively easy to cut and cost-effective.

 

Here are the parts I used. Evertything but the fan can be sourced at Home Depot:

 

2- 3 x 5' sheets of hardi-backer ($20)

1-8 ft section of flexible metal ducting ($10)

1- 140cfm 4" inline fan (all metal contruction...sourced at a "grow" store on on ebay via a search) ($100 or less)

1- dryer wall vent- all metal. no plastic ($10)

1- 4" ducting elbow- metal

1 roll of foil duct tape (you need this stuff around the house anyway)

2 4" hose clamps (or use the tape above)

120V power source

 

 

I made my kiln base from 3 layers of the hardi backer board. To do this I laid a peice on top of the kiln and bent down and traced the underside....all around the kiln. When I flipped the board over...this gave me a template pattern of the basic size I would need to cut. Because I didn't want to have the base hang out from under the kiln whatsoever, I then shorted this measurement by 1".

 

I then stacked all 3 boards and clamped them together using c-clamps.... and cut out around the template shape. While the boards were still c-clamped together I then marked and cut out a 4" hole directly in the center of the template.

 

I then seperated the layers and carefully....with tin-snips....cut and bent a flange on one end of the 4" elbow and ran that through the 4" hole...and then taped the flange to the backer board. I then stacked the other 2 boards on top and used the foil tape toadhere/ cover the edges of the template. This held the 4" elbow in place well...affixed to the bottom of the kiln without a "spring" sytem like Skutt uses. I then atteched the ducting...and ran it to the fan that I affixed to the wall where I placed the vent outside.

 

Probably the scariest thing was drilling holes in the lid/bottom of the kiln. :lol:

 

Skutt said that their unit is operating correctly when a match flame could be sucked into one of the drilled holes in the lid while the kiln was in operation. I basically hooked everything up....fired up the kiln for a bisque.....and started drilling holes in the metal ducting elbow as things went along. I could see the factory unit had 2-3 1" or so diameter holes to suck in fresh/cool air into the ducting and out...so i had an idea of >about< how many 1/2" holes to drill...

 

Hopefully the pictures will help explain the above speel... glad to answer any specific questions if needed.

 

 

teardrop

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post-8561-133253744021_thumb.jpg

post-8561-133253750128_thumb.jpg

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OK....here we go:

 

Preface: I bought a barely used Skutt 818 in Denver for a song. It had a stand but no vent system. I immediately found the EnviroVent install manual/product info online and started digesting it/trying to see how/what was required/etc...

 

Without a vent the bottom of my kiln is bare brick. The stand...being angled steel stock....contacted the brick and could easily cause damage/wear so I knew I needed to protect it. Fortunately the kiln had only been moved once before I moved it and was owned by the person who originally bought it.

 

It appeared to me that the stock vent system was made of sheet metal but I not only don't have decent access to such material I've also worked with it enough as a machinist to know that it is a pain/can easily cut you/etc. without the proper tools/gear....so I started looking for a cost effective/easily sourceable alternative.

 

what I came up with is 1/4" thick "hardi-backer board" that is used to strengthen floors/shower stal walls/etc. so they can accept tile. Easily sourced at Home Depot/etc....it is non-flammable....relatively easy to cut and cost-effective.

 

Here are the parts I used. Evertything but the fan can be sourced at Home Depot:

 

2- 3 x 5' sheets of hardi-backer ($20)

1-8 ft section of flexible metal ducting ($10)

1- 140cfm 4" inline fan (all metal contruction...sourced at a "grow" store on on ebay via a search) ($100 or less)

1- dryer wall vent- all metal. no plastic ($10)

1- 4" ducting elbow- metal

1 roll of foil duct tape (you need this stuff around the house anyway)

2 4" hose clamps (or use the tape above)

120V power source

 

 

I made my kiln base from 3 layers of the hardi backer board. To do this I laid a peice on top of the kiln and bent down and traced the underside....all around the kiln. When I flipped the board over...this gave me a template pattern of the basic size I would need to cut. Because I didn't want to have the base hang out from under the kiln whatsoever, I then shorted this measurement by 1".

 

I then stacked all 3 boards and clamped them together using c-clamps.... and cut out around the template shape. While the boards were still c-clamped together I then marked and cut out a 4" hole directly in the center of the template.

 

I then seperated the layers and carefully....with tin-snips....cut and bent a flange on one end of the 4" elbow and ran that through the 4" hole...and then taped the flange to the backer board. I then stacked the other 2 boards on top and used the foil tape toadhere/ cover the edges of the template. This held the 4" elbow in place well...affixed to the bottom of the kiln without a "spring" sytem like Skutt uses. I then atteched the ducting...and ran it to the fan that I affixed to the wall where I placed the vent outside.

 

Probably the scariest thing was drilling holes in the lid/bottom of the kiln. :lol:

 

Skutt said that their unit is operating correctly when a match flame could be sucked into one of the drilled holes in the lid while the kiln was in operation. I basically hooked everything up....fired up the kiln for a bisque.....and started drilling holes in the metal ducting elbow as things went along. I could see the factory unit had 2-3 1" or so diameter holes to suck in fresh/cool air into the ducting and out...so i had an idea of >about< how many 1/2" holes to drill...

 

Hopefully the pictures will help explain the above speel... glad to answer any specific questions if needed.

 

 

teardrop

 

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I read your post with a lot of interest as I have my kiln in our small garage/shop and the fumes can get bad in winter when the door cannot be left open. What size holes and how many did you drill in the lid of the kiln?

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Esther,

 

I followed along with much of what the Skutt manual said here http://www.skutt.com/pdf/envirovent2/Envirovent2_Manual.pdf

 

for my kiln...I drilled 2 - 3/16" holes in the lid and one 3/16" hole in the base. Larger kilns appear to need more holes so check out the guide in the book for your specific needs.

 

hope that helps

 

teardrop

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The flexible duct that connects my electric kiln to the exhaust system (and from there outside) keeps cracking. So far I have been patching it with aluminum tape, but I'd like to replace the duct itself. Is it safe to use a replacement duct from Home Depot designed for clothing dryers? If not, what is safe to use? I fire the kiln to 2400 degrees, but I don't know how hot the duct will get.

 

 

You can use 4" PVC pipe provided it is approved by your local building codes. This document covers installation of the down-draft vent:

 

http://www.paragonwe...nuals/ACF18.pdf

 

Sincerely,

 

Arnold Howard

Paragon Industries, L.P., Mesquite, Texas USA

ahoward@paragonweb.com / www.paragonweb.com

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