Jump to content
MartinB

Kiln Venting Airflow

Recommended Posts

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

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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.

 

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites
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!

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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?

Share this post


Link to post
Share on other sites
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

Share this post


Link to post
Share on other sites
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.

Share this post


Link to post
Share on other sites
11 hours ago, neilestrick said:

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.

Neil 

I disagree

Properly designed and cooled fans are rotary devices they last a long time. The environment is usually well defined and mitigating the operation hazards by design is essential. Longevity varies due to products that are not reasonable quality, designs that create overly harsh operating conditions or lack of reasonable maintenance. Centrifugal chillers, building fans, heating unit fans,  ceiling fans, exhaust fans, jet and turbofan engines are rotary devices. They last when properly designed and attended to. If you are experiencing premature failure of a fan, something is likely wrong.

I have many designs in service for 20 years or more without failure or replacement.

Share this post


Link to post
Share on other sites
8 minutes ago, Bill Kielb said:

Neil 

I disagree

Properly designed and cooled fans are rotary devices they last a long time. The environment is usually well defined and mitigating the operation hazards by design is essential. Longevity varies due to products that are not reasonable quality, designs that create overly harsh operating conditions or lack of reasonable maintenance. Centrifugal chillers, building fans, heating unit fans,  ceiling fans, exhaust fans, jet and turbofan engines are rotary devices. They last when properly designed and attended to. If you are experiencing premature failure of a fan, something is likely wrong.

I have many designs in service for 20 years or more without failure or replacement.

I was referring specifically to fans used for venting kilns and studio dust, like what was described above, not ceiling fans or jet engines. If the fan was just pulling air through it I would agree that it should last a long time. But when it's pulling abrasive clay dust, moisture and fumes from the kiln, etc, it's going to affect the life of the fan. I've replaced enough kiln vent fans to know that they don't just wear out due to age. They corrode.

Share this post


Link to post
Share on other sites
1 minute ago, neilestrick said:

I was referring specifically to fans used for venting kilns and studio dust, not ceiling fans or jet engines. If the fan was just pulling air through it I would agree that it should last a long time. But when it's pulling abrasive clay dust, moisture and fumes from the kiln, etc, it's going to affect the life of the fan. I've replaced enough kiln vent fans to know that they don't just wear out due to age. They corrode.

Poor design or less than good install. Seen a bunch. The ratio of room air to kiln air makes the exhaust stream  super reasonable. The hours of use, not much compared to lots of fans that run 24/7. If it doesn’t last five years, start looking for why.

Share this post


Link to post
Share on other sites
1 hour ago, Bill Kielb said:

Poor design or less than good install. Seen a bunch. The ratio of room air to kiln air makes the exhaust stream  super reasonable. The hours of use, not much compared to lots of fans that run 24/7. If it doesn’t last five years, start looking for why.

I'm talking about downdraft vent fans that were installed to manufacturer's instructions- Skutt Envirovent, L&L Vent-Sure, Orton Ventmaster, Vent -a-Kiln hoods, etc. The fans are completely corroded when they die, from the fumes and moisture from the kiln. For CeramicJim, the more clay dust he sucks through it, the shorter its lifespan. The more firings he uses it to vent, the shorter its lifespan. It could very well be that there are better ways to design the systems, but for most people that's not an option, because most people don't have a background in HVAC installation. Plus the lifespan of a vent fan is about number of firings, not number of years. If you only fire once a week, your vent system will last a lot longer than someone who fires 5 times a week.

Share this post


Link to post
Share on other sites
1 hour ago, neilestrick said:

I'm talking about downdraft vent fans that were installed to manufacturer's instructions- Skutt Envirovent, L&L Vent-Sure, Orton Ventmaster, Vent -a-Kiln hoods, etc. The fans are completely corroded when they die, from the fumes and moisture from the kiln. For CeramicJim, the more clay dust he sucks through it, the shorter its lifespan. The more firings he uses it to vent, the shorter its lifespan. It could very well be that there are better ways to design the systems, but for most people that's not an option, because most people don't have a background in HVAC installation. Plus the lifespan of a vent fan is about number of firings, not number of years. If you only fire once a week, your vent system will last a lot longer than someone who fires 5 times a week.

All good  points but five years would be my reasonable minimum on virtually any decent system. Fans that are corroded generally ingest far too much kiln air to makeup air.  setting the  home made aside for a bit if you don’t get five years out of a decent kiln system something is likely not great about the setup. So for the lifespan of a kiln vent fan I would shoot for that minimum expectation. As far as longevity, more dilution air, less heat through the fan, life is generally good. 

More cfm is not necessarily the answer. Starving  and overheating  a large fan seldom end with good results. Air changes per hour are no longer a reasonable standard. Have seen many a paint booth improperly designed and operated. Almost as many rotting kiln vents with insufficient room air.

There must be a  reasonable way to help the clay community. This stuff is complicated but actually relatively simple. Although I have seen many a bad HVAC design as well so maybe just too tough for many to understand.

Share this post


Link to post
Share on other sites
6 minutes ago, Bill Kielb said:

All good  points but five years would be my reasonable minimum on virtually any decent system. Fans that are corroded generally ingest far too much kiln air to makeup air.  setting the  home made aside for a bit if you don’t get five years out of a decent kiln system something is likely not great about the setup. So for the lifespan of a kiln vent fan I would shoot for that minimum expectation. As far as longevity, more dilution air, less heat through the fan, life is generally good. 

More cfm is not necessarily the answer. Starving  and overheating  a large fan seldom end with good results. Air changes per hour are no longer a reasonable standard. Have seen many a paint booth improperly designed and operated. Almost as many rotting kiln vents with insufficient room air.

There must be a  reasonable way to help the clay community. This stuff is complicated but actually relatively simple. Although I have seen many a bad HVAC design as well so maybe just too tough for many to understand.

How about a big weed fan, 10 incher and just turn the whole studio into a wind tunnel for a bit?  You don't need to worry about acid vapor, hot moist air or even ducting.  Add a carbon filter on the intake and you've got even more protection.  Works for me anyway!

I actually cheat and have my kiln outdoors.  Every chemist and engineer knows that outdoors is a magical place where fumes disperse without coaxing.  Can't afford a fume Hood? No problem! Just do it outdoors!  I love it!

Speaking of which, i have a bunch more resin lustre experiments to conduct but its been raining cats and dogs outside and all of the ingredients used react violently with water... Dang ole magical outdoors, only makes a good fume Hood for 6 weeks out of the year here!

Share this post


Link to post
Share on other sites
2 minutes ago, liambesaw said:

How about a big weed fan, 10 incher and just turn the whole studio into a wind tunnel for a bit?  You don't need to worry about acid vapor, hot moist air or even ducting.  Add a carbon filter on the intake and you've got even more protection.  Works for me anyway!

I actually cheat and have my kiln outdoors.  Every chemist and engineer knows that outdoors is a magical place where fumes disperse without coaxing.  Can't afford a fume Hood? No problem! Just do it outdoors!  I love it!

Speaking of which, i have a bunch more resin lustre experiments to conduct but its been raining cats and dogs outside and all of the ingredients used react violently with water... Dang ole magical outdoors, only makes a good fume Hood for 6 weeks out of the year here!

Our saying in the late 80’s and 90’s for IAQ::The solution to pollution is dilution .......... with, outdoor air of course. That was great until humidity levels became excessive beyond the reasonable dehumidification capacity of equipment and the mold problem was born! Of course mold is everywhere, especially ........ outdoors.

Share this post


Link to post
Share on other sites
21 hours ago, Bill Kielb said:

All good  points but five years would be my reasonable minimum on virtually any decent system.

I don't think I've ever seen a downdraft vent last less than 5 years now that they don't mount the motors under the kiln.  I've got 11 years and 2000 firings on one of my downdrafts. Vent-A-Kiln hoods seems to last forever.

21 hours ago, Bill Kielb said:

There must be a  reasonable way to help the clay community. This stuff is complicated but actually relatively simple. Although I have seen many a bad HVAC design as well so maybe just too tough for many to understand.

All of the kiln vents on the market work very well. I think the've struck a good balance between ease of installation, functionality, and price. Yes, you can build a better system for less money, but for the average customer it's a good, simple solution to the venting problem.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.