Vent fan still allows fumes

[ronfire]

I have a direct vent from the kiln to the outside and always has a negative  pressure inside the kiln  even close to the end of firing.

I still get a strong sulphur smell when the kiln is in the last hour of firing.

Should I increase the draw on the kiln  or is this usual even with the vent or add another vent hole in the kiln floor?

So far I just limit my time around the kiln during that time but still have to check on it from time to time.

[Bill Kielb]

You need to limit the temperature of the exhaust through the fan to let’s say 100-130  degrees with bypass or room air. Going above this temp begins to shorten the life of the fan and ductwork. If you are already at this point  and self limit for the above reason then this fan will not be able to perform any better. If  your exhaust temperature is low, you can simply decrease the amount of room air or add another hole to the kiln. 

Which to do depends on the fan, available area of the hole  for room air, etc........ Ideally you want the fan to perform near its peak capacity so the room air hole needs to be sized to perform at full capacity of the fan and then establish the best number of holes into the kiln. The example would be starving the fan excessively would also decrease it’s available suction. Manufactures generally engineer this out with their stuff so you don’t need to think too much about it.

I would double check the holes into the kiln and make sure they have not become obstructed first.

Normally wax smell is the thing that’s hard to remove but that only occurs approximately in the 400 to 800 degree range, top end smells are not real,common.

Here is a link fro an old design I did to replace one of these things and pick up as much wax smell as practical. It might give you some insight.

 

[Magnolia Mud Research]

11 hours ago, ronfire said:

I have a direct vent from the kiln to the outside and always has a negative  pressure inside the kiln  even close to the end of firing.

I still get a strong sulphur smell when the kiln is in the last hour of firing.

Do you have a flow of makeup air coming into the kiln room (area)?  
The room should be pressured above the outside air pressure to prevent the “smelly stuff” from coming back via the low pressure inside.

 

LT

[Mark C.]

Factiod

One of the worst smells on an electric kiln is firing it up with a cat spray on the exterior. WOOOOO that is a real nasty mix at temperature

Ok see your sulfer smell is so much better now.

[Bill Kielb]

2 hours ago, Magnolia Mud Research said:

Do you have a flow of makeup air coming into the kiln room (area)?

Not a bad idea but the reality of combustion air or this small exhaust comes from the volume of his room and infiltration. It is actually preferential even where infiltration is measurably small. We are likely talking the equivalent of a bathroom fan or less. Commercial downdrafts measure on the order of less than 20 cfm. If it we’re 100 though I doubt any space would be tight enough to inhibit it as long as it’s open to a decent volume and not stuck in an air tight room.

“The room should be pressured above the outside air pressure to prevent the “smelly stuff” from coming back via the low pressure inside.”
The room needs to be negative with respect to adjoining spaces. Pressurizing would be wrong. Simply exhaust the room to outdoors, no worries you will not pressurize the planet.

[neilestrick]

Three possibilities:

1. It's not pulling enough from the kiln because of the setup. Adjust the room/kiln air mix to pull more from the kiln.

2. You need another hole in the lid. Most kilns are drafty enough that holes aren't a big deal, but sometimes they're needed. I've got one kiln that was too tight and needed a hole to vent properly.

3. The room is too tight and there's not enough air coming in. This would be less likely, but I've seen it happen. If the kiln is in a small room with the door closed, try cracking a window or opening the door to allow air from the adjoining spaces.

[Dick White]

In addition the above suggestions about venting to the outside and having a source of makeup air to replace the negative pressure of the air being vented out - if you are using an open window or door to allow makeup air in, be sure that opening is on a different side of the room or building from where your vent exhaust is. If your intake location for the makeup air is near the exhaust point, the stinky air will just get pulled right back into the room in a vicious circle.

[Magnolia Mud Research]

4 hours ago, Dick White said:

In addition the above suggestions about venting to the outside and having a source of makeup air to replace the negative pressure of the air being vented out - if you are using an open window or door to allow makeup air in, be sure that opening is on a different side of the room or building from where your vent exhaust is. If your intake location for the makeup air is near the exhaust point, the stinky air will just get pulled right back into the room in a vicious circle.

My grandpa  taught me to always stand up wind of the fire!.   

That also applies to kilns.  

[ronfire]

The kiln is in a 20'x40' shop and has large sliding doors that will not seal well so not worried about makeup air, the exhaust is on the opposite side where air would come in, So I am thinking maybe another hole in the bottom of the kiln to allow more flow. The lid and sections are never air tight so I don't think a 3rd hole in the lid would be the first starting place. Will have to add a hole before tomorrow before I fire again.

 

 

[neilestrick]

1 hour ago, ronfire said:

The kiln is in a 20'x40' shop and has large sliding doors that will not seal well so not worried about makeup air, the exhaust is on the opposite side where air would come in, So I am thinking maybe another hole in the bottom of the kiln to allow more flow. The lid and sections are never air tight so I don't think a 3rd hole in the lid would be the first starting place. Will have to add a hole before tomorrow before I fire again.

What size and quantity of holes do you currently have, and what size kiln? Is this a commercial vent (Envirovent, Vent-Sure) or one you made yourself?

[Bill Kielb]

Again, I think you need to know what is the temperature of the air being exhausted when the kiln is at top temp? From there, less room air (more suction) or bigger holes or more holes if you prefer.

Your room is big enough to acceptably pick up makeup air by volume and infiltration of the adjacent room or space it expands to without worry of sucking gas appliance fumes back in. It’s actually generally allowable by code even for natural vent gas appliances. If we were installing a bath fan no one would worry. Your kiln is likely way less than a bath fan.

We start to worry when folks install larger exhausts say  200 cfm and up  that they have a sufficient source of makeup air. Room volume and allowable makeup air infiltration is well defined in most gas appliance codes.

A picture or two likely helps  clarify all this.

[ronfire]

The fan is from a wood stove blower and is a 2 speed, on high it does not move more air so I am thinking it is restricted with the input. I currently have 2  - 1/4" holes in a Skutt 1027. This is what the eco vents call for a kiln that size but I think I will up it to 3/8 holes.. Not worries about makeup air as there is enough gap under the doors.

Here is a pic of the fan I am using, it does not list cfm. The vent is right behind the kiln so the plumbing is short.

[Hulk]

~110 cfm

per the only ref I found (a FB post)...looks like Timber Ridge doesn't make the stove that fan fits any longer.

Looks like that (64-2812) isn't Timber Ridge part number; looks like the vendor's number

https://heatredefined.com/collections/parts/products/ac-16

Between

  a) enough air moving through the kiln to supply oxygen for thorough and efficient bisque and the glaze effect we/I want and

  b) enough "pull" on the kiln to prevent any leakage of fumes to the surrounding area

may be where you are with your setup.

An overhead evacuation system to remove heat and escaping fumes might be in order?

My diy kiln vent is still working great, however, diy overhead hood fan died last month; the replacement is ready to go, just have to install it - today's a good day for that! My overhead's intake doubles as nuisance dust remover; I set up to measure powdered glaze ingredients on top of the kiln, voila! ...once wetted, I'm moving glaze buckets (I do two gallon buckets) to the workbench for mixing, etc.

 

[Bill Kielb]

4 hours ago, ronfire said:

pic of the fan I am using, it does not list cfm. The vent is right behind the kiln so the plumbing is short.

Gonna be tough to get more than 100 cfm with reasonable mixing manifold. More interested in how you get a mix of kiln air and room air really. What size are the holes that let room air in? If the exhaust temp is too low, you can restrict the room air further to increase suction. It’s the whole system that counts. Without a picture of your pickup it’s hard to have an opinion other than what temp is the exhaust at top kiln temp?

[neilestrick]

Commercial downdraft kiln vents use 146cfm fans, so the recommended hole sizes probably aren't going to work for you.

[ronfire]

I cant find any information on the cfm of the fan, even the link Tom posted does not list it. the draft hole I have below the kiln is a 1" hole that is only 3/4 open. I used to have a 2nd kiln on the system so the Y is now closed off and all the joints are taped closed.

The kiln will suck in a flame from a lighter all the time during the firing, this is why I do not understand why the fumes.

 

[neilestrick]

1 hour ago, ronfire said:

The kiln will suck in a flame from a lighter all the time during the firing, this is why I do not understand why the fumes.

Is the lid lifting a lot at the high end of the firing? If the gap is getting too big it could be spoiling the draft.

[neilestrick]

On 11/16/2020 at 10:03 PM, Mark C. said:

One of the worst smells on an electric kiln is firing it up with a cat spray on the exterior. WOOOOO that is a real nasty mix at temperature

The very worst is cat spray on the inside. I worked on a kiln once that made cat pee steam when I started it up.

[Bill Kielb]

8 hours ago, neilestrick said:

Commercial downdraft kiln vents use 146cfm fans,

Their free air performance, but in operation with restriction on return and supply, not even close. I’ve measured them. No real mystery though we are looking on the order of 4” reduced to a couple 3/4” - 1” inlets.

[Bill Kielb]

5 hours ago, ronfire said:

The kiln will suck in a flame from a lighter all the time during the firing, this is why I do not understand why the fumes.

Still curious how hot this gets. Too much it will condense and create a smelly hydrocarbon mess that will eat your ductwork and fan. The smell might actually be from the ductwork. I have seen several drippy messes when folks hooked them straight to the kiln with no bypass air. Much of the water and chem fumes condense on the interior of the ductwork. Might be the source of your smell actually. The equipment should suck smoke in, not necessarily a lit flame.

[ronfire]

The duct work is warm but does not get hot to the touch. I seams to be warm as much from the closeness to the kiln as it is from the drawn in heat.

[Bill Kielb]

I would check at 2000 degrees if it’s Luke warm then  this would contradict being able to pull the flame of a lighter. . Any fan capable of pulling a flame from a lighter in is likely pulling lots of kiln air. A bit of a mystery though since I assume it is pulling hard. I would love to see a pic of the mixing box, it’s impossible to tell from that photo. Also would love to see it pulling the flame from the lighter, especially 1500 degrees and above. 2000 degrees, generally not something left to burn off, many simply switch the fan off to save energy and firing time. This may be consistent someway with your cracking issue on the bottom of the kiln.

[ronfire]

Here is a pic of the mixing box, not very clear. There is a pipe that will slide on the inner pipe that has holes in it. Currently I have it set to have only 1 hole open.  With the amount of negative pressure in the kiln I am surprised at the fumes I get just before the kiln reaches the top temp for cone 04 bisque. It is most noticeable on a bisque firing. When I test with a lighter on a removed plug or at the to holes on the lid the draft will bend the lighter flame inward.  I would get a pic of it but cant find a standard type lighter that works now,

The lid does not appear to shift open during firing, I adjusted the hinge to eliminate that problem.

So far my solution is to not be in the shop at that time except to check on the kiln, that is ok but still don't like it. It has been much easier to deal with now with the new controller instead of a sitter.

Wonder if it would be better to change over to a top vent system instead and not draw air into the kiln. It would not be hard to change the fan over and hang a movable hood.

 

 

[Bill Kielb]

Top vent gets more kiln heat so that would be a plus. A bending lighter is generally too extreme. This is piped to full 4” all the way and only has maybe 1 inch diameter hole so I would say it is causing you likely more trouble than you think.  Likely the cracking issue as well. If you have the tools, generally for the holes manufactures suggest in the kiln, you need about 0.1” negative measured near the connection to kiln to suck enough but not too much kiln air out. Down drafts don’t get everything so wax smell often is a complaint.

Your automatic kiln control should have  a relay output to turn the fan on and off through most of the firing. It is only a pilot duty output though so it can only drive a small relay or kiln relay if you will.

Hood vents are more effective at capturing smells and kiln heat. Here  is a video that details the basic idea.

 

[neilestrick]

I love how that video shows fumes billowing out of the kiln even though a downdraft is being used . Ridiculous! Under normal firing circumstances that would never happen. But those hoods do work very well for removing fumes and heat. I've installed them in many homes and schools and everyone has been very happy with them. The downside is that they don't pull oxygen into the kiln like the downdrafts do. Of course, you could always use both systems. I've hooked up many downdrafts on kilns that also have overhead hoods.