Diy Downdraft Vent

[Pieter Mostert]

I'd like to build my own downdraft vent, and would appreciate answers to a number of questions. I have a lot of questions, so don't feel obliged to answer all of them.

Based on the manuals for the Orton Vent Master, L&L Vent-Sure and Skutt EnviroVent 2, the main components I will need are:

• Collection cup with adjustable opening that sits under the kiln
• A blower
• A flexible duct connecting the collection cup to the blower

Besides figuring out the specs of these components, I need to be sure I can obtain these (preferably locally - I'm in South Africa, and shipping from the US is expensive. We also have a never-ending post-office strike).

I'd like to make my own ceramic collection cup. The main problem with this is connecting the duct to the collection cup. However, I should be able to make a sleeve sticking out of the collection cup on one side with a diameter roughly equal to that of the duct, and can use a hose clamp or silicon adhesive to attach the duct around the sleeve. If it isn't completely airtight, this shouldn't be a problem. For the adjustable opening, I'll have one or more holes in the sides of the cup. The cup will sit on a larger slab, so that I can place half-bricks around the cup to partially block the holes, thus controlling the air-flow.

I'm not sure if I'll be able to obtain the standard kiln-vent blower (Dayton 1TDP7 PSC - mentioned by Neil Estrick in a previous post) locally. Would any other blower with a high enough CFM rating work as well, or is there something about this design that makes it good for kiln vents?
 
Grype mentioned it was difficult to find ducting, but I will try a local company that makes vents. There might also be a possibility of getting some used duct for free, but I need to check the length and diameter. Any thoughts on what type of material (aluminium / galvanised steel / high temp black flex hose) works best?

Is anything I've outlined above a terrible idea? Is there anything I could be better or more easily at the same price?

Some more questions:

•  What should the dimensions of the collection cup be? Does using a cube with interior side length of 4" seem about right? (I'm using inches since most folks on this forum seem to use them; apologies if you prefer the metric system). Should I put a 1" hole on each side of the box other than the one where the duct connects to it?
•  L&L, whose blower is 130 CFM, mentions that vents can overpower smaller kilns. My kiln, a Paragon TnF-82, has a volume of only 3.3 cubic feet, so I think a blower with a smaller CFM rating is necessary and sufficient. The Orton Vent Master has a CFM of 60 - 80, and is good for kilns up to 14 cubic feet. Assuming the same ratio of CFM to kiln volume will work for my kiln, I should be fine with a blower having a CFM of 20, but I'm not sure whether this assumption is justified. If I do use a weaker blower, should the hole I drill in the bottom of the kiln have a diameter larger than 1/4"?
• Should I drill a hole in the lid? Orton and Skutt recommend this, while L&L says this isn't necessary. There is an existing hole in the centre of the lid (1/2" diameter, I think), but Orton and Skutt recommend the hole be drilled 1" from the inside of the kiln wall. Is this because the resulting airflow is better? Should I leave things as they are and drill a hole later if necessary?
• What size holes should I put in the duct, and how far apart should they be spaced?

[Mug]

The air cup: I would make the cup air tight then put a couple of  doors that pivot to adjust the air intake.

The reasoning behind this is if you have air leaks that are unaccounted for it will be harder to adjust.

Some people have used metal electrical boxes for their air cup.

The spring loaded air cup that one of the kiln vent mfg use is an excellent idea to compensate for thermal expansion and contraction, but it may be hard for you to make.

Blower: I would use one made of metal and make sure the fan blades are metal. The heat coming out should be less than what you would get from a blow dryer, but plastic has no place in a kiln vent. Make sure the motor is on the outside, not inline where it could corrode.

Vent holes: The 1/2" vent hole in the kiln top is too big and should be plugged. The small hole drilled close to the side is for better circulation. but you may not need it, the kiln will draw air in from around the door....Try it see what you think.

Tubing: Solid metal where you have straight sections. You can get away with flexible metal dryer vent for the curves, but you will need to inspect it before each use, clay and glaze fumes are corrosive. 

[Denice]

I had bought a Skutt Envirovent 2 but wanted to put it on 2 kilns,  my husband made the cup out of a parts washer can that had a spring top that you pushed down do get more cleaning fluid.  He turned it upside down and then plumed it in, it is a very basic small parts washer he had never used because he has a better one.  You could probably find one at a store selling automotive parts, I'll ask him exactly what he did if you decide to go that way.  Denice

[Mark C.]

As far as the motor you need a squirl cage motor with those same CFM ratings. I do not think its rocket science one that comes close or exceeds a bit will work. I'm sure the one Neil posted is a solid replacement-just order one with the same specs.

As far as the venting keep it all metal so these is no fire hazard.

Mark

[Pieter Mostert]

Thanks for the feedback everyone.

Mug, as long as the unaccounted airflow is consistent and not too great, I don't see why you couldn't regulate the airflow by adjusting the size of the openings in the cup. Do you think the floor of a 25.5" wide kiln would flex enough during firing to require a spring loaded air cup? The floor bricks are in bad shape, but I'll put the kiln on a 1/4" thick steel plate with a hole cut in the centre.

Denice, do you know what type of parts washer it was? It may be worth a try if it's relatively inexpensive.

Mark, I may be able to get a blower with a CFM rating of about 120, but need to check if it's all metal. I'm not convinced that a less powerful blower won't be able to do the same job though.

[Mark C.]

The spring most likely is because kilns expand and contract with the heat cool cycles .That keeps it tight no matter what the cycle.

Mark 

[MichaelP]

http://community.ceramicartsdaily.org/topic/5366-diy-kiln-vent/

[Pieter Mostert]

I've seen your pictures, MichaelP, but I don't possess your metalworking skills, which is why I want to make a ceramic collection cup. It'll also mean I don't have to worry about the cup corroding.

[Mug]

If you drill miscellaneous holes it will be a lot harder to get the the air set. Different sized kilns will require different sized intake holes. The kiln vent manuals describe how to properly adjust your intake.

Neatness counts when you build something yourself. If you build something in a haphazard way it will cause you grief. I feel the adjustable vent doors will save you time and grief.

The Skutt Enviro vent version does not use adjustable doors. You could try to make a similar design.

 

As Mark said you want all metal.

I would not use ceramic for the cup.

[Joseph Fireborn]

I didn't like the squirrel cage blower because of how you have to mount it. I didn't have to mount mine in the wall, so that particular blower was more difficult than an inline blower with similar CFM ratings. I also didn't like all the extra parts required for it to mount, where the inline just needed, 2 duckings and 3 clamps.

 

Also remember that you can adjust the amount your taking out of your kiln with your holes, so the CFM's dont have to be exact as you can adjust the flow yourself. In fact its pretty obvious it doesn't have to be the same since they sell the same blower for kilns of huge differences in sizes, or at least that was my take on it.

 

I just bought a simple inline blower(similiar CFM) and mounted it to a 2x8 that I cut in to a 3 foot section. I have the L&L box under my kiln, and then I have a piece of metal ducking from the box to my inline blower, then another ducking from the other side of the blower that runs out garage door. I lower my garage door to 3inchs from the floor and put a pad lock on the door so no one can pull it open when I run my kiln at night.

 

If your going to run your metal ducking through the walls, be safe and put metal parts where the ducking goes into the wall. Even though the piping should never be really really hot its better safe than sorry.

[Pieter Mostert]

Also remember that you can adjust the amount your taking out of your kiln with your holes, so the CFM's dont have to be exact as you can adjust the flow yourself. In fact its pretty obvious it doesn't have to be the same since they sell the same blower for kilns of huge differences in sizes, or at least that was my take on it.

 

I agree, it's just a question of what CFM blower will still work for a 3.3 cubic foot kiln. I suspect that my initial guess of 20 CFM is too small, since the wind can be quite strong, and I don't want fumes being blown back into my studio. In any case, the smallest metal fan with an external motor that I've been able find locally has a CFM of 127. Amazon doesn't seem to ship blowers to South Africa (or maybe I haven't looked hard enough), so I'll probably have to find something local.

 

I'm thinking of running the exit duct through a broken pane in a glass door - still need to figure out exactly how that will work. I'm renting my studio, so can't really be drilling holes through walls.

[Joseph Fireborn]

You need to get more than less on the blower, look up the specs on the L&L blower(dayton i think) and get something close to it.

[MichaelP]

No need for the extra holes in the collection cup at all.  Make them in a rigid part of the pipeline connecting the collector and your fan. The openings can be easily made adjustable through the use of a hose clamp or a similar device partially covering the holes.

 

I'd, probably, make the holes closer to the collector just to keep the rest of the line cooler and somewhat less prone to corrosion.

[Joseph Fireborn]

http://www.hotkilns.com/sites/default/files/pdf/ventsure-instruct.pdf

 

We recommend one vent system for kilns up to approximately 20 cubic feet.

 

 

That vent is 140 CFM. So anything around that will be fine for your kiln, as they used that for kilns up to your size down to 2CuF

 

Also there is a guide for how many holes to drill etc in that article as well.

[neilestrick]

The L&L system has two major benefits over the the Skutt or Orton system. First, the collection box on the L&L is screwed to the kiln stand (on L&L kilns) or to the side of the kiln (on other brands) so that it can't be bumped out of position. Half of the kilns I see that have the spring loaded cup have the cup pushed aside so far that it's no longer lined up with the holes in the floor, due to people kicking the duct work while loading the kiln. Second, the collection box is adjustable so that you're not pulling more air from the kiln than is necessary to remove the fumes, and therefore not affecting firing and cooling times unnecessarily.

 

L&L does not recommend drilling holes in the lid of the kiln unless it's just not venting properly. Generally there are enough openings in the kiln that sufficient air can be drawn in for venting, especially as the kiln heats up and the lid start flexing. That said, I did have to drill a single hole in the lid of my E18T-3 because kilns that small tend to be tighter than larger kilns and it just wasn't getting enough air to vent properly.

 

The way these vents work is that they pull just enough air from the kiln to remove the fumes, and mix that kiln air with a lot of room air to cool it down. The mixing should take place as close to the kiln as possible (collection cup/box) to avoid corroding/melting your ductwork with too much heat. The temperature of the air going out the wall should be under 150F degrees, no hotter than a clothes dryer.

 

If you build with a large enough fan you can add another kiln to the system later. I've put two kilns on many systems and they work just fine. I've got a single fan on my 20 cu/ft kiln, but I use two collection boxes, which evens out the draw and allow me to get more room air into the mix than a single box.

[ronfire]

I know this is an old thread but I thought I would add to it

Just finished building my vent system but have not run it yet. My kiln sits on a steel plate that I have a 4" heating duct attached to the plate by bending the tabs over the plate. The first section of 4" pipe has 5 - 1" holes in it that can be covered by a sleeve that I made from more heating duct. Air mixture will be adjusted by closing over some of the holes. I used a blower fan designed for airtight fire place blower and vents out the wall through a drier vent. My kiln is an old scutt 231,   6.9 cu ft I think so Scutt recommends 3 holes 3/16 in the bottom of the kiln. I will not require hole in the lid a the kiln has enough gaps between sections. If I can not get air drawn into the kiln I may increase the holes to ¼ inch as per L&L specs.

Hope it all works well, will try it tomorrow after I empty the glaze load in it now cooling.