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MartinB

Kiln Venting Airflow

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Hi there,

I'm looking to vent my kiln and had a question on the amount of airflow. I have a Rohde EcoTop 60 litre which has a vent attachment. I also have a 6" extractor fan in the studio which I was just using to dump heat outside. At its lowest setting it shifts 400 cubic meters per hour or  111 litres per second.

If I attach this directly to the kiln vent is it going to be pulling too much air and make the kiln struggle to reach temp? I can't really find much information on this....

Thanks for any help

Martin

Rohde_uitlaat_toplader

 

 

Edited by MartinB

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I actually just found some documentation for Skutt's kiln venting system which runs at 140CFM which translates to 66 litres a second, and thats for use with kilns much larger than mine, so my extractor fan is way too powerful it seems.

Edited by MartinB

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Hi Martin!

Kiln vents I've seen or read about exert enough "pull" on small hole(s) in the kiln (kiln bottom, or side near the bottom) such that another small hole (in the lid) is necessary for make up air; the rest of the flow comes from ambient, through a mixing box, where the ambient vent is adjustable. The kiln atmosphere is very hot and typically corrosive, hence mixing with ambient is a good idea - cools it down and dilutes the yucky gases.

Perhaps these pics may help? They show flow through aforementioned inlet and outlet holes (however, in practice, air may be sucked in through cracks, around the edges, etc. ...and some kiln atmosphere may escape as well) and ambient making up most of the flow - see "Room Temp Air Entering Bypass Box"

Any road, immediately diluting the kiln atmosphere is a must (imo)!!

There must be sufficient make up in the kiln area/room as well - to (easily) make up for all the air being pulled out of the room by your fan system(s).

Test the flow with a smoke punk (incense stick will work) or lighter flame (careful with that!) - so you can see that atmosphere is sucked into the kiln; re-test when firing, as the behavior will be a bit different.

I made up a bypass box out of galvanized sheet, bought an inline fan and some ducting, and made holes in the wall and kiln -it works! If I were starting over, I'd go with a bigger/stronger fan.

 

60 liters, hmm... less than three cubic feet; your fan may be strong enough to serve your current kiln and your next kiln as well!

The "bypass box" with sufficiently large and adjustable ambient vent - that's the ticket.

 

see vent.JPG

see vent ii.JPG

Edited by Hulk
maths

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Hulk is correct. Kiln vents pull a small amount of air from the kiln, and mix it with a large amount of air from the room, so the air going through the system is below 150F. I would contact the kiln manufacturer and see what they recommend for use with their attachment.

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Thanks for the info, I'll get in contact with rohde for more details on the power of the extractor, the one I have is waaay to strong.

The adaptor is an open tube that sits over the top bung hole so draws air from the room over the hole, and there's a little vent hole on the bottom of the kiln that can be opened and closed.

Annoyingly the vent adaptor that came with the kiln is the wrong size,  I never bothered to check it when the kiln was delivered.

 

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Definitely contact the manufacture. Many of these smaller kilns with this type of connection can be system powered as in the natural updraft created by the buoyancy of the air. Many have tables pertinent to their kilns. The table and pictures below do not apply to your model but are an example of what your manufacture has likely prepared for your kiln.

2618D54C-C435-4602-92BD-A3973F573EDE.png

A6DCBC27-EE2A-4552-B2F3-E3593524DBA3.png

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1 hour ago, Bill Kielb said:

Definitely contact the manufacture. Many of these smaller kilns with this type of connection can be system powered as in the natural updraft created by the buoyancy of the air. Many have tables pertinent to their kilns. The table and pictures below do not apply to your model but are an example of what your manufacture has likely prepared for your kiln.

Thanks Bill, that diagram is the same style of venting my kiln has and really helped clear things up in my head. I hadn't considered that the extractor fan isn't directly sucking through the kiln but is drawing air over the bung hole, so a higher flow rate would be needed. I've emailed rohde and am waiting their response, I wish their manual was as detailed as that!

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So after all of that i don't need an extractor fan on it, it works on convection. The nabertherm manual was really clear in explaining it and Rohde just emailed to say that style of kiln doesn't need one. I wish their manual had been a bit clearer. 

Thanks for all your help!

image.png.986ac103441370429e52824716423b3b.png

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I've vented my kiln in similar ways before. Does anyone have issue with longevity of the fan? I had one before that ceased pretty early on in its life.  Since then I've just moved towards a large a powerful window fan vent near by the kiln. It sucks 180CFM which is more than powerful enough to grab the heat and fume from the kiln. I don't have a picture. I've made a detailed build video here. Just trying to share a crazier unorthodox idea. It was much cheaper than your typical vent a kiln system. Thoughts?

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1 hour ago, CeramicJim said:

I've vented my kiln in similar ways before. Does anyone have issue with longevity of the fan? I had one before that ceased pretty early on in its life.  Since then I've just moved towards a large a powerful window fan vent near by the kiln. It sucks 180CFM which is more than powerful enough to grab the heat and fume from the kiln. I don't have a picture. I've made a detailed build video here. Just trying to share a crazier unorthodox idea. It was much cheaper than your typical vent a kiln system. Thoughts?

We analyzed  and built something simple. Part of the essential point of the design was to keep the blower cool so it lasted because we noticed folks just adding bigger and bigger blowers without sufficient bypass air.  The goal in the video was to introduce the concept of bypass or room air mixed with a very small amount of kiln air. I think the design stacks up as well or better and includes some above kiln ventilation. For two kilns for about 250 bucks using all decent parts and should have a  high use studio life of five to ten years or more.

take a look: see what you think 

 

Edited by Bill Kielb

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9 hours ago, CeramicJim said:

I've vented my kiln in similar ways before. Does anyone have issue with longevity of the fan? I had one before that ceased pretty early on in its life.  Since then I've just moved towards a large a powerful window fan vent near by the kiln. It sucks 180CFM which is more than powerful enough to grab the heat and fume from the kiln. I don't have a picture. I've made a detailed build video here. Just trying to share a crazier unorthodox idea. It was much cheaper than your typical vent a kiln system. Thoughts?

The longevity of a fan varies greatly depending on environmental conditions. Saying it will last for X number of years is impossible, but it should last for at least several years. However now that you've done all the hard work, replacing it in the future will be much quicker.

When venting heat and fumes from a room, it's all about how quickly/often the air in the room is changed. When sizing a fan, HVAC folks do calculations to size the fan to the both the size of the room and the amount of heat given off by the kiln. There are standards that they shoot for in their calculations. Your system may work very well for your situation, but a 185CFM fan may be terribly undersized for someone with a larger room or a larger kiln. Just as a point of reference, Vent-A-Kiln hoods use a 265CFM fan on hoods for 23" wide kilns.

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