Nancy Braches on sat 21 oct 06
Hi everyone
So I've been researching changing the way I vent my kilns and based on my research, I found a way to vent them for about $50 with items found at Lowes. Any input on my idea would be greatly appreciated.
I purchased a 6" duct fan for $27, a 6" to 4" duct reducer and the aluminum stretchable duct for dryers. I then purchased a 4" to 3" reducer and a piece of 4" steel pipe that will fit in the bottom peephole of my kiln.
I plan to put the steel pipe into the bottom peephole and then put the 3" reducer over it and that is attached to the dryer vent which attaches to the duct fan and that will pull air out of the kiln through the duct and then to the outside dryer vent.
The cost for all the parts were less than $50. Does anyone have any input...do you think it will work? or is it a bad set up? bad idea? good idea?
Thanks in advance
Nancy
Nancy
Hilltop Pottery
http://pg.photos.yahoo.com/ph/hilltoppottery/album?.dir=/e4e8re2&.src=ph
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Nancy Braches on sun 22 oct 06
Wow and thank you all for the great advice. I guess my research wasn't as thorough as I thought it was. I have so many things to review and look at now. I checked the cfm on the duct fan I purchased and it is 450cfm so I think it's probably too big.
I'm back to researching for a smaller cfm and more research on the amount of air I need to pull through the kiln.
I'll post an update soon!
Nancy
Nancy
Hilltop Pottery
http://pg.photos.yahoo.com/ph/hilltoppottery/album?.dir=/e4e8re2&.src=ph
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Wayne Seidl on sun 22 oct 06
Nancy:
Check the cfm rating (cubic feet per minute) on that fan. Most kiln vents
run around 45-50 cfm. It will cost you time and money in heating to vent
your kiln faster than that. (The heated air would get sucked out before the
heat did its work.) Unless of course you plan to vent using a hood over the
top of the kiln and not directly connected to it, in which case you can use
any cfm you want.
Just my .02
Best,
Wayne Seidl
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Nancy Braches
Sent: Saturday, October 21, 2006 11:40 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Making a vent out of duct parts....any input?
Hi everyone
So I've been researching changing the way I vent my kilns and based on my
research, I found a way to vent them for about $50 with items found at
Lowes. Any input on my idea would be greatly appreciated.
I purchased a 6" duct fan for $27, a 6" to 4" duct reducer and the aluminum
stretchable duct for dryers. I then purchased a 4" to 3" reducer and a
piece of 4" steel pipe that will fit in the bottom peephole of my kiln.
I plan to put the steel pipe into the bottom peephole and then put the 3"
reducer over it and that is attached to the dryer vent which attaches to the
duct fan and that will pull air out of the kiln through the duct and then to
the outside dryer vent.
The cost for all the parts were less than $50. Does anyone have any
input...do you think it will work? or is it a bad set up? bad idea? good
idea?
Thanks in advance
Nancy
Nancy
Hilltop Pottery
http://pg.photos.yahoo.com/ph/hilltoppottery/album?.dir=/e4e8re2&.src=ph
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Steve Slatin on sun 22 oct 06
Nancy --
I see two possible issues off the top of my head ... the first is
that a vent fan designed for another use might well draw too
much volume from the kiln. This could keep you from making
temperature on a firing. The second is that parts of your
setup -- I focused first on the aluminum ducting (aluminum
melts at 1220 F, probably below your firing temperature), but that's
just an impression -- may not hold up well to the extremely
high temps of kiln gasses right as they exit the kiln. It's
pretty easy to burn out a commercial vent fan by exposing
it to very high temperatures, also.
Have you examined commercial vent systems? The ones
I've looked at are set up to mix room-temperature air with
kiln gasses at the moment they exit the kiln. This allows
for a low volume flow of atmosphere from the kiln (dealing with
the first issue I raise, above) while lowering the temperature
that the mechanism has to withstand (dealing with the
second). The actual cross-section of the drilled-hole
systems also are less than the cross-section of a peep...
Just as a design parameter, I'd recommend some approach
that would permit these changes. Since you're removing the gasses
from the lower peep, perhaps you could rig something so
that the removal point would be deliberately 'leaky' -- a
loosely fitting surround for the peep, rather than a tightly
fitted pipe going inside, maybe? and if the peep could be
partially covered by something you could control the
area from which atmosphere would be withdrawn. That
way the (presumably fixed-velocity exhaust fan) can move
a pre-cooled, adjustable colume of kiln gasses through the
aluminum duct.
Someone -- it may have been Maurice Weitman -- sent me
some pictures of a homemade vent that cost him about
$50. Right now I can't put my hand on those pictures, so
I can't be sure who sent them to me ...
Disclaimer -- I've never done this myself, just a few ideas,
etc.
Best wishes -- please let us know what you do and how
it works -- Steve Slatin
Nancy Braches wrote:
Hi everyone
So I've been researching changing the way I vent my kilns and based on my research, I found a way to vent them for about $50 with items found at Lowes. Any input on my idea would be greatly appreciated.
I purchased a 6" duct fan for $27, a 6" to 4" duct reducer and the aluminum stretchable duct for dryers. I then purchased a 4" to 3" reducer and a piece of 4" steel pipe that will fit in the bottom peephole of my kiln.
I plan to put the steel pipe into the bottom peephole and then put the 3" reducer over it and that is attached to the dryer vent which attaches to the duct fan and that will pull air out of the kiln through the duct and then to the outside dryer vent.
The cost for all the parts were less than $50. Does anyone have any input...do you think it will work? or is it a bad set up? bad idea? good idea?
Thanks in advance
Nancy
Nancy
Hilltop Pottery
http://pg.photos.yahoo.com/ph/hilltoppottery/album?.dir=/e4e8re2&.src=ph
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Mark Tigges on sun 22 oct 06
On Sat, Oct 21, 2006 at 08:39:34PM -0700, Nancy Braches wrote:
> Hi everyone
>
> So I've been researching changing the way I vent my kilns and based on my research, I found a way to vent them for about $50 with items found at Lowes. Any input on my idea would be greatly appreciated.
>
> I purchased a 6" duct fan for $27, a 6" to 4" duct reducer and the aluminum stretchable duct for dryers. I then purchased a 4" to 3" reducer and a piece of 4" steel pipe that will fit in the bottom peephole of my kiln.
>
> I plan to put the steel pipe into the bottom peephole and then put the 3" reducer over it and that is attached to the dryer vent which attaches to the duct fan and that will pull air out of the kiln through the duct and then to the outside dryer vent.
Hi Nancy. I put together something similar. You can view it here:
www.m2crafts.ca/vent.html
I did something slightly different than you. First, I vented through
the floor of the kiln, not through a peephole. I did this because
it's what commercial vents do. Second I used a blower, 90 cfm.
Reason for that is that I wanted it to last. The gasses coming out of
the kiln are not very friendly. Third, I put a diffuser in. This
allows you to mix the kiln exhaust gas with ambient before it hits the
fan. Two reasons, cool the gas going through the wall, and allow
tuning of the draw on the kiln.
I believe that the aluminium tubing will corrode rather quickly. When
I first made the duct, I used a diffuser that I built from sheet.
When I built a new kiln, I used a floor heating register instead. The
one I built after only 20 firings or so showed a considerable amount
of corrosion.
Good luck,
Mark.
--
http://www.m2crafts.ca
m2crafts [at] gmail
Maurice Weitman on sun 22 oct 06
At 20:39 -0700 on 10/21/06, Nancy Braches wrote:
>So I've been researching changing the way I vent=20
>my kilns and based on my research, I found a way=20
>to vent them for about $50 with items found at=20
>Lowes. Any input on my idea would be greatly=20
>appreciated.
>
>I purchased a 6" duct fan for $27, a 6" to 4"=20
>duct reducer and the aluminum stretchable duct=20
>for dryers. I then purchased a 4" to 3" reducer=20
>and a piece of 4" steel pipe that will fit in=20
>the bottom peephole of my kiln.
>
>I plan to put the steel pipe into the bottom=20
>peephole and then put the 3" reducer over it and=20
>that is attached to the dryer vent which=20
>attaches to the duct fan and that will pull air=20
>out of the kiln through the duct and then to the=20
>outside dryer vent.
>
>The cost for all the parts were less than $50.=20
>Does anyone have any input...do you think it=20
>will work? or is it a bad set up? bad idea?=20
>good idea?
Hello, Nancy,
You don't say what kind of kiln you have (I assume it's electric).
And I'm not sure what kind of research you did,=20
but you may have gotten some bad impressions of=20
how a kiln vent should work.
Most vents that are sold by kiln manufacturers=20
use a tiny (~1/8") hole to extract air from the=20
kiln. AND they don't use the full force of the=20
vacuum from the fan/blower... most have the=20
flange that connects up to the kiln a short=20
(again, about 1/8" to 1/4") distance away from=20
the kiln to allow lots of cool air to commingle=20
with the hot air from the kiln.
This not only reduces the amount of air sucked=20
from the kiln (and therefore the amount of cool=20
make-up air needed), but it also reduces the=20
temperature in the duct, and perhaps as=20
important, it dilutes the nasties in the exhaust=20
that might serve to corrode the ducts and fan.
You don't say how long your duct is but if it's=20
more than a few feet, I would suggest using rigid=20
ducts instead of the flexible aluminum "heater=20
vent" ducts. Not only will it last much longer,=20
but it will offer less resistance to the flow,=20
since it's smooth. My vent uses a centrifugal=20
blower from a bathroom exhaust vent, and is about=20
twenty feet away from the kiln. It also has four=20
90=BA or so turns. But it draws very well.
Also, I've experimented with various ways to=20
introduce make-up air. Some vent and/or kiln=20
manufacturers suggest using an open peep. Some=20
rely on the lack of seal in the lid-wall=20
junction, and others suggest using tiny holes=20
drilled in the lid.
It is very, very important that the system be=20
"tuned" so that the amount of air taken from the=20
kiln is just enough to maintain a slight negative=20
pressure inside. In that way, nothing will be=20
tempted to leak out. You can make it so that=20
there's a higher negative pressure to speed the=20
exhaust, but then you risk introducing too much=20
cool air onto your hot pots too soon.
Testing whether the vent is drawing properly is=20
often done by putting a smoking object (a snuffed=20
candle, for instance) right next to a make-up air=20
entrance and observe it entering the kiln.
There's one more thing that in my research got=20
filed under the heading Too Much Information, but=20
in the spirit of full disclosure I offer it here.=20
As the temperature gets very high in the kiln,=20
the smaller holes tend to be more restrictive and=20
in fact, less air will go through. This, it=20
turns out, is a Good Thing, since most of the=20
nasties have long since departed, and since it is=20
more dangerous to introduce cold air into the=20
kiln. But it can be a concern if you were to=20
test the effectiveness of the vent at high temps=20
and see that not much air is being drawn into the=20
kiln. Fyi, fwiw, etc.
As with many things discussed on clayart, each=20
method has its adherents and detractors.=20
Shocking I tell you. For what it's worth, I've=20
tried all of the above and think the exhaust vent=20
at or near the bottom and make-up air holes=20
drilled into the lid work best. For me. In my=20
kilns.
I hope this makes sense to you.
Regards,
Maurice
Vince Pitelka on sun 22 oct 06
> I plan to put the steel pipe into the bottom peephole and then put the 3"
> reducer over it and that is attached to the dryer vent which attaches to
> the duct fan and that will pull air out of the kiln through the duct and
> then to the outside dryer vent.
Nancy -
Two things to consider. First, the standard vent systems sold for toploader
kilns suck a very small amount of air through very small holes drilled
through the brick. That's all the circulation you need to draw off all the
toxic fumes and even out the temperature. If you hook a pipe up to the
lower spyhole, you will suck ALL of the heat out of the kiln very quickly,
and your kiln will never get to temperature. A great deal of research went
into the design of those "down-draft" kiln vent systems, and they all work
in about the same way, so if you want to build a kiln vent system, it
doesn't really make any sense to stray very far from that design.
Second, the blowers for those vent systems are designed so that there are
bleeder holes on the intake housing, allowing room-temperature air to mix
with the kiln fumes before entering the blower. If you were sucking a
larger amount of heat out of the kiln without mixing cool room air into the
system, you would immediately overheat your blower.
Good luck -
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Snail Scott on mon 23 oct 06
At 11:50 AM 10/22/2006 -0700, Maurice W wrote:
>As the temperature gets very high in the kiln,
>the smaller holes tend to be more restrictive and
>in fact, less air will go through...
Could you elaborate on this? -Snail
Michael Wendt on mon 23 oct 06
Nancy,
Everyone else has covered the key points
except for two:
1. In my experience, the kiln vent will pull
enough air through the sensor rod hole
onto the junior cone to cool it and change
its reading so you must use witness cones
if you leave the vent running throughout the
firing.
2. The kind of fan you purchased will work
fine even if you operate it very near total
air cutoff. Contrary to what most people
believe, a fan motor does the most work
when its intake is least restricted. If you
think of a vacuum cleaner as an easy to
test example, turn it on and listen to the
pitch change as you cover the inlet hose
by different amounts. At full cutoff, the
motor races up to peak rpm. This can only
happen because the load has been removed.
It is similar to what happens when a car hits
an icy patch on a road.
So what does this mean to your vent?
A large fan will not pull any more air from
the kiln than a small one if you follow the
advice of the other posters which was:
a. a few tiny holes in the lid
b. a few slightly larger holes in the center
of the bottom
c. an adjustable connection to tune the
amount of extraction versus dilution air
d. placing the fan at the end of the vent
pipe so that it blows out of the room
and keeps the entire pipe below
atmospheric pressure in case the pipe
ever develops leaks.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, Idaho 83501
USA
wendtpot@lewiston.com
www.wendtpottery.com
Maurice Weitman on wed 25 oct 06
At 09:32 -0500 on 10/23/06, Snail Scott wrote:
>At 11:50 AM 10/22/2006 -0700, Maurice W wrote:
>>As the temperature gets very high in the kiln,
>>the smaller holes tend to be more restrictive and
>>in fact, less air will go through...
>
>Could you elaborate on this? -Snail
Well, Snail, in a word, maybe, but I'm not sure how helpful it will be.
I spent quite a bit of time looking through my archived notes to find
the source of that tidbit but came up nearly empty.
I remember the explanation having something to do with "boundary
layer" in fluid mechanics.
As it sounds, in the case about which we've been discussing, there is
a region around the inside of the hole that is, or acts as a boundary
layer and restricts flow.
One reference I couldn't find dealt with large increases in heat of
the wall surrounding the hole resulting in increases in the size of
the boundary layer. The smaller the hole, the more the impact of heat
has on the restriction of the flow.
I'll keep on looking for the exact reference, but I remember thinking
that the explanation corroborated the observations I made.
Sorry for the vagueness.
With any luck, one of our resident REAL scientists will chip in with the facts.
Regards,
Maurice
Fredrick Paget on sat 28 oct 06
>At 09:32 -0500 on 10/23/06, Snail Scott wrote:
>>At 11:50 AM 10/22/2006 -0700, Maurice W wrote:
>>>As the temperature gets very high in the kiln,
>>>the smaller holes tend to be more restrictive and
>>>in fact, less air will go through...
>>
> >Could you elaborate on this? -Snail
>
>
>With any luck, one of our resident REAL scientists will chip in with
>the facts.
>
>Regards,
>Maurice
>
>______________________________________________________________________________
I don't claim to be a "real scientist" I was just an engineer before
I retired quite a few years ago, So I looked in my trusty 'Handbook
of Engineering Fundamentals (Esbach) and the formula for pressure
drop through a pipe nozzle or orifice has the pressure drop directly
proportional to the absolute temperature in degrees Rankine.
So Maurice is right.
Fred Paget
--
Twin Dragon Studio
Mill Valley, CA, USA
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