Kiln vent setup

[thiamant]

Hello, Im going to write another post since this topic was brought up somewhere else...

I'm concerned about fumes releasing from my kiln because it's located in my house. I have a Nabertherm small kiln (60L). So these are the manufacturer indications for vent system:

 

I was thinking on doing something like that (its a passive system) to exhaust the kiln. My supplier suggested me not to use a fan extractor because it would also extract a lot of temperature and therefore more power consumption and/or less kiln durability (kW out, kW in). In fact, the manufacturer recommends closing the bottom valve at approximately half firing so that the kiln can keep the temp up efficiently. So instead, I thought I would just turn on a fan from the inside of the room pointing to the window. Any suggestions? Can I just use aluminum flexible tubes? Can I substitute the chinese bell for a horizontal reflector? I want to be as minimal as possible since it's a small kiln and also I don't have much room for a very complex setup. My main concern is fumes, not heat.   @liambesaw @Bill Kielb

[liambesaw]

2 hours ago, thiamant said:

Hello, Im going to write another post since this topic was brought up somewhere else...

I'm concerned about fumes releasing from my kiln because it's located in my house. I have a Nabertherm small kiln (60L). So these are the manufacturer indications for vent system:

 

I was thinking on doing something like that (its a passive system) to exhaust the kiln. My supplier suggested me not to use a fan extractor because it would also extract a lot of temperature and therefore more power consumption and/or less kiln durability (kW out, kW in). In fact, the manufacturer recommends closing the bottom valve at approximately half firing so that the kiln can keep the temp up efficiently. So instead, I thought I would just turn on a fan from the inside of the room pointing to the window. Any suggestions? Can I just use aluminum flexible tubes? Can I substitute the chinese bell for a horizontal reflector? I want to be as minimal as possible since it's a small kiln and also I don't have much room for a very complex setup. My main concern is fumes, not heat.   @liambesaw @Bill Kielb

If your kiln is having trouble reaching temperature while vented, that means it is underpowered.  Kiln vents are not a strong flow of air coming through the kiln, they are fairly passive and are designed to remove fumes.  A fan in a window is good enough for a garage, or detached building, but if your kiln is in a living area, I would suggest getting a vented hood or bottom vent, whichever your kiln manufacturer recommends.  

 

[Bill Kielb]

4 hours ago, thiamant said:

I'm concerned about fumes releasing from my kiln because it's located in my house. I have a Nabertherm small kiln (60L). So these are the manufacturer indications for vent system:

 

FWIW- IMO
The nabertherms are a bit different than the powered downdrafts in the US. From memory they are also adjustable in that they can be opened  and closed as desired. So, the height of the stack is the thing that generates the flow. (Just like a chimney) the 1.5m  (minimum) requirement above the top of the kiln in the drawing is just that and raising the height will generate more suction. So you may want to raise it to closer to  two meters, providing the model you have allows adjustment of this flow. The vent can be used to ventilate during firing and speed up the cool down of the kiln, all within reasonable limits of course.

So I believe your sales representative is correct as the kilns with powered fans have just a few small holes drilled into the kiln (maybe 6-7 mm each) this kiln has a larger hole so installing a fan would likely be too much. That said, these types of vents do not capture ALL the fumes, they just don’t........ but passive vents are goof proof and heat energy becomes the energy source, so a very efficient proven way to do things.

So as long as you have enough suction (maybe the  extra half meter) and some built in way to regulate so you do not remove too much heat I think that would provide good flexibility for you, and ......... a reasonable fan in the window blowing out with somewhere for fresh air to come into the studio would serve you best. If possible the fan and window closest to your kiln and the fresh air source on the other side of the room if possible. One might say cross ventillation.

[neilestrick]

Powered vents are the norm in the US, and they only pull a very small amount of air through the kiln so they don't really affect the function of the kiln. They do have the benefit of bringing fresh air and oxygen into the kiln which increases element life and makes glazes look better. The draft of the vent also help kilns fire a little bit more evenly.

I don't think anyone on this forum has a passive vent system so we won't necessarily be a lot of help with the specifics, so follow the recommendations from Nabertherm. I think my first concern would be using the correct type of ducting. With powered vents the hot air from the kiln is mixed with cool air from the room, so the exhausted air is under 60C. With your passive system there doesn't appear to be a method for cooling the exhaust air, so I would imagine the ducting will get a lot hotter, especially near the kiln. So check with Nabertherm and do whatever they say, because they are the experts with that system.

[Bill Kielb]

1 hour ago, neilestrick said:

With your passive system there doesn't appear to be a method for cooling the exhaust air, so I would imagine the ducting will get a lot hotter, especially near the kiln. So check with Nabertherm and do whatever they say, because they are the experts with that system.

FYI - There is a bypass inlet, they label it bypass effect. This method is fairly old and traditional BTW.

[thiamant]

5 hours ago, Bill Kielb said:

a reasonable fan in the window blowing out with somewhere for fresh air to come into the studio would serve you best. If possible the fan and window closest to your kiln and the fresh air source on the other side of the room if possible. One might say cross ventillation.

The problem is that the only source for fresh air comes from this window. That is why I place the fan inside the room like this:

FAN --> KILN ||| WINDOW

Is there a more efficient way? Like blowing air from the window into the room instead?

 

Btw, I dont mind if I cant remove ALL the fumes, as long as sufficient is done and they dont travel to other rooms in the house thats fine. I never stay in the kiln room while it s firing anyway.

[Bill Kielb]

7 minutes ago, thiamant said:

Is there a more efficient way? Like blowing air from the window into the room instead?

In my experience
Best way is to nearly Always suck air out which means fan in the window. Air will leak in from the rest of the house to replace it. It’s nearly impossible to build an airtight house. One could always open a window in another part of the house, it will travel to the room to makeup the air being exhausted.  Pure suction or exhaust will capture the particles much more effectively.

In the US, the only commercial systems that we can technically get approved in a meaningful way would be an exhaust hood. So all suction above the appliance.

Blowing the air will make some of the air bounce off the walls and ceilings and get distributed back into the room for you to breath, so I would not try to blow over the kiln and then through the window unless there was no option to just run exhaust.

[thiamant]

@Bill Kielb so something like this?

 

KILN ||| FAN --> WINDOW

[Bill Kielb]

Yes, they do make fans that fit in the window which would be best as this helps ensure all the air exhausted goes outside and little to none reflected back into the room.

[neilestrick]

8 hours ago, Bill Kielb said:

FYI - There is a bypass inlet, they label it bypass effect. This method is fairly old and traditional BTW.

Totally missed that! So this isn't really doing anything as far as bringing air into the kiln, it's just catching whatever comes out the spy hole and not even doing a great job of that. The problem then is that the spy hole isn't the only place that fumes come out of the kiln- the lid gap will also allow leakage. I certainly wouldn't trust this system to do the job. That's probably why I have never seen a passive duct on a spy hole in 30 years of ceramics.

@thiamant I'd put a fan in the window, or get a powered vent system. Either one will do a better job than the passive system. It's easy to rig up a way to temporarily set a fan in the window. They make low cost window fans that pull 400CFM or more, that would probably do a pretty good job.

[Bill Kielb]

1 hour ago, neilestrick said:

The problem then is that the spy hole isn't the only place that fumes come out of the kiln- the lid gap will also allow leakage.

In my experience
It’s a staple in many designs but hidden by the fact we are used to them. The chimney likely being the popular recognizable precursor. So as folks discovered that hot air rises and they could amplify its effect by making things taller it really has formed the basis of chimneys, hoods etc...  with dilution air providing a form of self tempering. It is self powered if you will, so that is significant. Their minimum heights in their drawing should reflect their tested product requirements.

As far as being effective, it might be as effective, more effective, or superior at only high temperatures and inferior at low temperatures. It’s hard to say. Electrics draw so little air and expecting them to maintain counter flow velocity to offset the natural buoyancy is a tough ask.

Air moves because of pressure difference, self powered system draw more as the temp goes higher, for electric systems, fan performance falls off rapidly as air gets hotter and thinner.

Tuned draft beats forced draft or mechanically induced  for simplicity and materials in most other instances. Who would want to force draft 500,000 btu kiln with an electric fan? Tough and expensive to do, but if done then a new level of precision in firing efficiency is available for an appropriate first cost and maintenance cost.

Steamboilers were a thing because they are easy and the steam pressure is used to move the energy through the system. No large pumps required to circulate water. Similarly natural draft devices perform well when designed, and they are self powered so I am not convinced it is better or worse really, just an old tried and true method. Having the pickup at the top of the kiln is likely more efficient at ventilating it as air moves because of pressure difference and buoyancy. Counterflow on the other hand is supposed to be more even. Properly designed and installed they probably both work similarly.

[neilestrick]

29 minutes ago, Bill Kielb said:

Similarly natural draft devices perform well when designed, and they are self powered so I am not convinced it is better or worse really, just an old tried and true method.

I have nothing against natural draft venting- I've used many gas kilns set up that way that worked well. I've even seen a couple of natural draft hoods over electric kilns. I just don't think a small duct over one spy hole on an electric kiln is the proper application for it.

34 minutes ago, Bill Kielb said:

Who would want to force draft 500,000 btu kiln with an electric fan?

Do you mean in terms of venting? The vast majority of overhead hood kiln venting systems have electric fans, especially for large gas kilns. Like, every university kiln room.

[Magnolia Mud Research]

12 hours ago, thiamant said:

The problem is that the only source for fresh air comes from this window.

that is the problem! 

To ventilate a room there must be an inlet source of fresh air and a separate outlet route for the exhausted air. These outlet exit must always be "downstream" of the of the environment of "fresh air" so that these two "airs" never mix, or the system will just be mixing/circulation device.  This simple requirement is seldom mentioned in instructions for installation of venting equipment, and in online discussions.   

If your window is the source of fresh air, you need to put the fan in the window pumping air in and install a separate route for the exit air to leave the room such as the diagram in your initial post with a vent pipe through the wall into a  chimney stack outside that terminates sufficiently high to keep the exhaust from being pumped back into the window by the fan.  

If you want to use the window fan to pump  air out then you must find a different source (not the window) of clean air to come into the room. 

remember: for each volume of exhaust air you pump out must be replaced by fresh air. 

LT
 

[Bill Kielb]

18 minutes ago, Magnolia Mud Research said:

If your window is the source of fresh air, you need to put the fan in the window pumping air in

I couldn’t disagree more strongly, that’s not how exhaust systems operate. Never pressurize a room that contains contaminants, ever! ALL leaks must be fresh air into the room so exhaust fans always pump to outdoors. When rooms are designed with supply and exhaust the exhaust will be designed to remove more air than the supply ensuring all leakage is fresh air in. Maybe easier to realize when one considers every commercial bathroom is either designed with all exhaust and no supply or significantly more exhaust than supply. We don’t want anything leaking out of the room contaminating our fresh air source.

Manufacturing clean rooms CAN BE pressurized so as not to allow unfiltered air in. Biological  and chemical hazard rooms must be very negative with respect to the adjacent rooms. Roof curb exhaust fans are a thing so all ductwork leakage will be into the exhaust stream and not contaminate any other area.

[Min]

21 minutes ago, Bill Kielb said:

I couldn’t disagree more strongly, that’s not how exhaust systems operate.

I guess we are reading @Magnolia Mud Research's post differently. 

21 minutes ago, Bill Kielb said:

Never pressurize a room that contains contaminants, ever!

From how I'm reading Lou's post I'm not seeing he is advising this. Replacing exhausted air volume with clean air into the room is how I'm reading it.

38 minutes ago, Magnolia Mud Research said:

If you want to use the window fan to pump  air out then you must find a different source (not the window) of clean air to come into the room.

 

[Bill Kielb]

2 hours ago, neilestrick said:

Do you mean in terms of venting? The vast majority of overhead hood kiln venting systems have electric fans, especially for large gas kilns. Like, every university kiln room.

A very designed item. All those universities have or had boilers that are natural vented. Fans cost money and constant volume fans only match one load at one point so wasteful. If they have to handle high temperature then there is that additional expense of more dilution air.

There are exceptions though, almost  all new appliances are now designed as  condensing these days so yes we meter the amount of gas in and the amount that leaves so very controlled  which gets the firing efficiency in the 90% range and requires a fan for metering exhaust over a very small range of temperature operation. But these items really not pertinent to a small kiln with a system powered method of exhaust.

So my bad, this gets to be a distraction from the point. Both systems are likely pretty equal in operation, one is self powered and one consumes some energy. The self powered has some distinct advantages over the powered and Vice versa. We have designed with it (buoyancy of air) for hundreds of years it’s very likely as effective or potentially better than the powered without the cost. Nabertherm has been around for more than 70 years  and is skilled in producing much larger furnaces, kilns etc...  so It really doesn’t appear their design is deficient IMO, just good use of energy.

[Bill Kielb]

2 minutes ago, Min said:

From how I'm reading Lou's post I'm not seeing he is advising this. Replacing exhausted air volume with clean air into the room is how I'm reading it.

41 minutes ago, Magnolia Mud Research said:

The statement quoted is the issue

   18 minutes ago,  Magnolia Mud Research said: 

If your window is the source of fresh air, you need to put the fan in the window pumping air in

Never pump air in and expect it to find its way out your designated source for an exhaust unless you are proficient at balancing powered supply and exhaust situations. Back to the bathroom example. Exhaust needs to suck everything to outdoors, the room MUST be negative in relation to the adjacent. Air moves by pressure gradient which means any interior space being exhausted must be negative with respect to others. I am not sure how to read the quote above differently.

[Magnolia Mud Research]

@Bill Kielb @Min  

Bill, I won't argue your choice of design.  

The main point is to make sure that the incoming air is equal of the air being exhausted with the fumes.  there are more one way to accomplish the requirement of having a safe environment in the kiln room.  This particular room, as presented, has some missing information (aka constraints) that must be considered before making a sound recommendation. 

My comments are focused on making the assumptions visible especially to the person that will make the final decisions.  

I made a poor choice of  the word "pumping" in the sentence: 
"If your window is the source of fresh air, you need to put the fan in the window pumping air in"

The point is that fresh air must be forced into the room, which means from an area of higher pressure than that in the room.  your explanation assumes the leakage rate is sufficient to remove the fumes created in the room and is sufficient to prevent the fumes exceeding the "an unstated" maximum concentration of fumes that will be allowed in the room;  that maybe true,  but if not, then the problem has not been solved.   

I have no preference of the designs available, but getting assumptions and constraints visible are important to make a sound decisions.  

LT

[Bill Kielb]

3 hours ago, Magnolia Mud Research said:

The point is that fresh air must be forced into the room, which means from an area of higher pressure than that in the room.  your explanation assumes the leakage rate is sufficient to remove the fumes created in the room and is sufficient to prevent the fumes exceeding the "an unstated" maximum concentration of fumes that will be allowed in the room;  that maybe true,  but if not, then the problem has not been solved.   

In the business it’s known as makeup air, so somewhere the suggestion was open a window in another adjacent room which is solid ordinary advice along with good undercuts on the door or even louvers as appropriate could be added. As far as designing a room to ventilate contaminants and / or maybe the sensible heat generated by the kiln  this would be known as makeup air to allow the exhaust fan to flow as designed.

A little about typical designs
His room must be negative, that’s how we design  nearly all exhaust situations, all leakage must be inward. As far as determining appropriate size, a simple tabular guideline for this situation would be air changes per hour which is a reasonable volumetric solution (with origins based in math and  dilution over time), Same for swimming pools BTW. if we know particle size and velocity as in paint spray booths that would be face velocity to capture the very small particles that could escape the booth (>100 fpm as I recall). Still clean rooms would be to maintain a certain measured pressure (likely less than 0.1” H2O) within the room  with known clean filtered air pumped in (A version of your suggestion but this is clean room stuff). Finally if he wants to include removing the heat generated by the kiln he needs to size to offset the known heat generated by enough cooling sourced from outdoor air it’s typical enthalpy  or perhaps  mechanically cooled to a more suitable state to reduce the amount of exhaust needed.

I am really fairly familiar with the typical design criteria. None of it really is based on the statement “to prevent the fumes exceeding the "an unstated" maximum concentration of fumes that will be allowed in the room; “, but all of it has been established over the years to help with effectively dealing with unknowns.

Most of that is way too complicated for a kiln owner, but forcing air in is never something we consider. Again, clean rooms force air out of them with the very clean air supplied to the room.

Makeup air is a thing for many good reasons and I will agree 100% that it is important, it is not necessarily to make sure the  exhaust fan will perform to its rating.  In this situation sufficient makeup air needs to be available for the fan to work well which in house fan terminology is open a window in another room, a fan blowing in is not necessary and  forcing air into this room will cause contaminated air to likely leak out places not intended. At no time do we ever want to pressurize the contaminated  room, ever or even mix the air in the room in a random way.

Now the one caution that’s usually missed but often needs to be stressed. If you install an exhaust fan anywhere that is sized so large it begins drawing fuel fired appliance fumes back down the stack and causing spillage this is an issue to guard against for large exhaust fans. Those appliances need combustion air and often dilution air for them to operate properly. I would agree 100% cautioning against that condition for sure and have in the past so I think your point should be that or intended to be that.

The problem with these kiln discussions is folks want to blow air into the room and open a window in the room  to let it out (really a pretty bad idea), just put the fan in the window blowing out and open a window in another room to let fresh air in. And yes, your fresh air inlet ought to be at least 10 feet or more away from where you are exhausting or any exhaust.

As far as equal in and out, not really necessary nor practiced in a room protected by exhaust ventilation, we want it negative with respect to all others that is the single most important aspect of exhaust and protecting against exfiltration. Do we want it excessively starved, the answer is no.  This is actually far too complicated for a few paragraphs, but pressurization does not fit this scenario and any reference to pressurizing this particular room is mistaken. It’s not a design choice, it’s the appropriate design choice. It’s not new, it’s  established practice.

[thiamant]

OK, so after reading the discussion I think I will follow Nabertherm recommendations for the updraft hood, and to be extra safe install a fan in the window pointing outside, then I will open a window from the other side of the house to help air circulation. 

So I have some limitations for placing the fan, because there is a small room in between and the only place where I can install the fan is in the window in between, something like this:

KILN ||| WINDOW1 ||| SMALL ROOM (<-- 1.1 meters --> || WINDOW2

So the fan can only be placed on window 1 but both windows can be open, the pipe exhaust would cross the small room until it reaches WINDOW2 and let the air out. 

Any suggestions for the fan? 

[neilestrick]

18 hours ago, Bill Kielb said:

just put the fan in the window blowing out and open a window in another room to let fresh air in. And yes, your fresh air inlet ought to be at least 10 feet or more away from where you are exhausting or any exhaust.

This is the answer that everyone is looking for. Please keep the OP in mind when answering questions, as most folks come to our forum in search of simple solutions. While we can't always provide that, we should still do our best to explain things in a concise, easy to understand manner. Many paragraphs with extensive use of trade jargon do not necessarily add clarity to this discussion.

[Bill Kielb]

On 5/23/2021 at 8:22 AM, neilestrick said:

This is the answer that everyone is looking for. Please keep the OP in mind

Understandable and a bit too complicated for sure but that was basically the original  answer provided to the OP.

[Bill Kielb]

On 5/23/2021 at 2:19 AM, thiamant said:

KILN ||| WINDOW1 ||| SMALL ROOM (<-- 1.1 meters --> || WINDOW2

So the fan can only be placed on window 1 but both windows can be open, the pipe exhaust would cross the small room until it reaches WINDOW2 and let the air out. 

Any suggestions for the fan? 

Not ideal but the exhaust needs to go in window 1. Window 2 is an ok distance, not great  for fresh air  but not ideal so opening a screen door further away from window 1 would be better. The pipe should be well above the windows so I would keep it away from window 2 as much as practical, most of the fumes will discharge from it. I looked up your kiln and it appears to have an adjustable inlet on the bottom. You should be able to find a nice setting that exhausts the kiln and not so excessive that it lengthens your firings. Raising the pipe .5 meter should get you more draw and further away from the windows so it may be something to consider. Their specs say 1.5 meter is minimum required vertical distance. If the pipe works suitably, you may not need a bunch of exhaust except to remove the excess heat.

[thiamant]

2 minutes ago, Bill Kielb said:

Not ideal but the exhaust needs to go in window 1. Window 2 is an ok distance, not great  for fresh air  but not ideal so opening a screen door further away from window 1 would be better. The pipe should be well above the windows so I would keep it away from window 2 as much as practical, most of the fumes will discharge from it. I looked up your kiln and it appears to have an adjustable inlet on the bottom. You should be able to find a nice setting that exhausts the kiln and not so excessive that it lengthens your firings. Raising the pipe .5 meter should get you more draw and further away from the windows so it may be something to consider. Their specs say 1.5 meter is minimum required vertical distance.

OK so to be more specific :

(| =W= | means pipe goes through window,)

KILN ROOM  (pipe goes up 1.25 m) | =W1= | SMALL ROOM (pipe goes up and crosses room (1.1m long 0.5m height) | =W2=| (Deflector) OUTSIDE

The fan is placed in W1 facing W2, and both windows can be opened during firing.

Total height is 1.75m, that's the best thing I can do.

I can open the kiln room's door but the adjacent room doesn't have a fresh air intake either, so I'm not sure that will help... I could open all the doors until it reaches the next air intake but I'm afraid of doing that and fumes going to undesired places in the house...

[Bill Kielb]

4 hours ago, thiamant said:

The fan is placed in W1 facing W2, and both windows can be opened during firing.

Total height is 1.75m, that's the best thing I can do.

Doesn’t sound good, sounds like whatever blows out W1, is blowing in W2. Not sure I understand, will make a sketch and attach here shortly @thiamant the picture  below is sort of what I was picturing your situation with a possible solution with a 1/2 window fan. Sorry for the rushed appearance but I am at the end of a conference call for work.