Skutt Envirovent still allows fumes

[MochiFriend]

I have a new, recently installed Skutt Envirovent 2 installed on my 818-3 kiln, venting out thru an exterior wall. Unfortunately I've noticed significant smells in the kiln room and adjacent areas in both bisque + glaze firings (bisque being worse). 

I've called Skutt a couple of times to trouble shoot, and have walked thru all of the most obvious/initial tests:
- Flame test works on all intake holes
- Checked to make sure no debris in the 2 intake + 1 outtake holes
- Vent's cup is centered on the kiln's bottom hole 
- No holes along vent ducting, which has a slight incline as recommended from the fan to the hole to the outside
- Checked to make sure vent itself is working from the outside, as warm air is coming out of the exhaust 
- Smell peaks during the 450-600F organics burn-off stage
- Bottom shelves sit 1" up from kiln floor
- Only thing I have not done is widen the hole at the bottom of the kiln. It is currently the recommended 3/16”. 

Skutt's customer service said that there will always be a "small smell", and Skutt's advertising for the vent says that it should result in "little to no fumes" in the kiln area. And while there's no quantifiable way to measure smell, I strongly believe that the amount of smell/fumes that I'm smelling is above this advertised "little to no fumes" level. 

The reason why I am so concerned is that I installed my kiln in the laundry room, which is adjacent to my basement. There is also my partner's office room immediately adjacent to the kiln/laundry room on the other side, which we open the door to and have 2 windows wide open during firings for air intake (don't worry, they're not on the same side of the vent on the outside, and there's a fence in between them too). All of this is on the first/basement-ish of our house, and the living space is right above. I swear I can feel it sometimes when the kiln is firing. And if I don't have the windows in the adjacent room open, I can smell the fumes around the peak 450-600F burn-off phase in the upstairs. 

We ran the kiln placement in the house by many folks, including my community studio teachers, local clay shop employees, vent installation guys, Skutt, etc. Everyone agreed that it was in a great spot! So I'm just at my wit's end because it seems like something is wrong with my vent and I can't figure out what it is. 

Thanks for reading, any help or advice is really appreciated!
I have long been a reader of many threads on this wonderful community. <3 

 

Edited December 2, 2023 by MochiFriend

[Bill Kielb]

1 hour ago, MochiFriend said:

Thanks for reading, any help or advice is really appreciated!

The counter flow vents can vent some of the fumes, even let’s say many fumes but they will not get them all. It cannot have enough power or airflow to offset the buoyancy of warm air. If it did, your kiln would not have enough power to make temperature because of all the air necessary being exhausted from the kiln would be a giant heating load.  Sort of like firing with the lid wide open. So here counterflow vents are a reasonable compromise solution.  Wax that burns off in the temperature range you describe is particularly noticeable but other fumes obviously are emitted, even those that most cannot smell. If we put a Pm2.5 particle detector (popular these days) in the vicinity you likely would see an immediate rise in particles detected when running your kiln. I mention this because the new IAQ indoor standards have made these air monitors accessible and relatively affordable these days. It does allow potters (with better accuracy than the smell test)  an easy way to verify with greater confidence their system appears to be performing as expected.
 

Without getting into a giant discussion of best practice, exhausting the kiln room and keeping it slightly negative (lower pressure) with respect to all adjoining spaces is a proven technique. From bathrooms to clean rooms, even surgical suites. This means an exhaust fan where some of the makeup air MUST come from the other spaces is important. We only want air leaking into the kiln room from other spaces. If you open a window in the kiln room and it supplies ALL the air to the exhaust  the kiln room will not be negative (lower pressure) with respect to the other rooms and exfiltration (or kiln odors leaking into other spaces) may still prove troublesome. These are fairly simple designs for folks that have done it; however well meaning or not, I have seen lots of well intentioned but less than ideal advice on this.

My thought is best to describe how it ought to work and you will be able to keep that fundamental in mind as folks suggest things. It needs to work just like a bathroom fan, only air is allowed to leak in from the other spaces. Simple really.

Your kiln vent could exhaust some of this air, but realistically the amount of actual exhaust is on the order of 10 cubic feet per minute. New bath fans will be 50 - 100 cubic feet per minute for some perspective. If you have a dryer that exhausts (non heat pump) then that machine will exhaust approximately 200 cubic feet per minute. You could test your next firing with it running to see if that will be sufficient exhaust to keep the room exhausted. If so, the addition of that sized fan might be a simple solution.

Edited December 2, 2023 by Bill Kielb

[MochiFriend]

Hi Bill,

Ah, I see. So with the principle of the kiln room being lower pressure than other rooms in the house —

I currently have the door to the adjacent office room open, as well as two windows in that office open. I have two box fans directing the air away from the kiln room and into the office room. My reasoning was that because the kiln room is smelly, I want to try to direct the smell in the air out of that room and towards the windows in the adjacent office. So currently: kiln room -> fans pointed towards -> office room -> windows 

Does that principle of the kiln room being lower pressure mean that I should instead be trying to bring the outside air into the kiln room from the adjacent office room? So: office w/ windows -> fans pointed into -> kiln room (and then ideally it gets sucked thru the kiln -> out thru the vent)? 

I have tried to illustrate this in my attached diagram. 

I'm not sure if I'm overthinking this but the vent seems to be struggling to pick up all the fumes so that's why I thought I had to "help it out" by airing out the rest of the room myself. Thanks very much for your thoughts and input into this. It's really helpful. 

[Bill Kielb]

15 minutes ago, MochiFriend said:

I'm not sure if I'm overthinking this but the vent seems to be struggling to pick up all the fumes so that's why I thought I had to "help it out" by airing out the rest of the room myself. Thanks very much for your thoughts and input into this. It's really helpful. 

 

The potential setup on the right is better, directing airflow often pressurizes things so often not effective or drives the smell into other spaces. Next time open you office window just a bit and run your clothes dryer no other fans. It’s about 200 cfm so that may give you a good idea how successful that sized fan will be. None of this will remove all the heat from the kiln, that takes quite a bit more exhaust and usually a hood over the kiln. 
 

If you think of it in terms of pressure rather than directing a stream of air you are much more likely to come to a best solution. So suction in the kiln room, air has to enter from all other locations.

Edited December 2, 2023 by Bill Kielb

[MochiFriend]

37 minutes ago, Bill Kielb said:

Your kiln vent could exhaust some of this air, but realistically the amount of actual exhaust is on the order of 10 cubic feet per minute. New bath fans will be 50 - 100 cubic feet per minute for some perspective. If you have a dryer that exhausts (non heat pump) then that machine will exhaust approximately 200 cubic feet per minute. You could test your next firing with it running to see if that will be sufficient exhaust to keep the room exhausted. If so, the addition of that sized fan might be a simple solution.

Got it (btw I responded to your message in the above message, but I'm new to the forums so not sure if I have to "quote" you for it to thread properly). Thank you. 

I've turned the fans in the office/kiln rooms to be facing IN towards the kiln room to create the negative pressure... we'll see if that helps! (though it'll be hard to tell at this point since I'm at the end of my bisque firing, but will observe for the subsequent glaze firing)

Before, I had turned the fans OUT of the kiln room to create a positive pressure path from the kiln room thru the office room and out the window. I figured if the fumes are going to hang out, I'd rather them follow my directed path out than float around indiscriminately my house. 

Regarding this last part of your message, my kiln is super small (Skutt 818 is about 2.5 cu). When you write, " You could test your next firing with it running to see if that will be sufficient exhaust", what do you mean by "it¨ — the existing kiln vent? Or the fans pointed in to the room? (At this point, the fans are pointed in towards the room so they are no longer exhausting the room. I have however not pointed the fan directly at the kiln to avoid messing with the firing). 

Thank you!!! Literally at my wit's end so this is all helpful. 

Edited December 2, 2023 by MochiFriend

[MochiFriend]

3 minutes ago, Bill Kielb said:

The potential setup on the right is better, directing airflow often pressurizes things so often not effective or drives the smell into other spaces. Next time open you office window just a bit and run your clothes dryer. It’s about 200 cfm so that may give you a good idea how successful that sized fan will be. None of this will remove all the heat from the kiln, that takes quite a bit more exhaust and usually a hood over the kiln.

Oh, I see haha. That's a neat idea but unfortunately I can't run the dryer at the same time — my kiln plugs into my 240v dryer outlet (it's the Skutt 818-3, which is adapted for this usage). Dryer is also on its separate venting system. 

[Bill Kielb]

1 minute ago, MochiFriend said:

Oh, I see haha. That's a neat idea but unfortunately I can't run the dryer at the same time — my kiln plugs into my 240v dryer outlet (it's the Skutt 818-3, which is adapted for this usage). Dryer is also on its separate venting system. 

The fans blowing in have a chance of pressurizing everything so I am trying to get you to an exhaust solution which we know will work. The kiln vent is such a small exhaust. I would feel better with a bath fan in the kiln room and the office window opened slightly as an easy test.

[MochiFriend]

10 minutes ago, Bill Kielb said:

The fans blowing in have a chance of pressurizing everything so I am trying to get you to an exhaust solution which we know will work. The kiln vent is such a small exhaust. I would feel better with a bath fan in the kiln room and the office window opened slightly as an easy test.

Ah, I see. Do you think it would be better to just not have the box fans going at all? 

I will definitely look into getting a bath fan installed in that room.  

On the topic of the kiln vent's exhaust strength, do you think there's any merit behind the idea of widening the kiln's bottom outtake hole more? It's currently 3/16. I saw a similar thread where the poster increased their hole, presumably from around that size to 5/16 and they noted it made a difference. (https://community.ceramicartsdaily.org/topic/23314-vent-fan-still-allows-fumes/page/2/#comments)

 

Thank you, thank you!! I'm so glad I posted here. 

 

Edited December 2, 2023 by MochiFriend

[Bill Kielb]

14 minutes ago, MochiFriend said:

Ah, I see. Do you think it would be better to just not have the box fans going at all? 

 

Yes, box fans likely will cause an issue. The kiln vent is way too small to suck all that air out.

a through wall fan close to the kiln more ideal. Just make sure there is always suction in the kiln room to be most effective. The only way to make something negative, you exhaust it outdoors. Intermediate fans likely will hurt more than help for the smell.

 

Edited December 2, 2023 by Bill Kielb

[MochiFriend]

5 minutes ago, Bill Kielb said:

Just make sure there is always suction in the kiln room to be most effective.

I'm understanding now what you mean by airflow/pressure — the suction framing is very helpful. I need to make sure the air is going generally towards the kiln because that's where the exhaust is (such that the air's flow is then thru the vent). 

Under this suction principle, I totally get that it would be best to have some kind of exhaust fan in that corner of the kiln room, however that is actually where a door to the basement is. (The basement isn't a super great option — it's directly below my bedroom, and the floor is uneven because where I live is quite hilly. It's basically the unfinished crawlspace/storage under the house). I've illustrated this in my diagram. I really appreciate this idea. 

I will remove the closest box fan blowing into the kiln room. The other one is helpful I think to still have in the office for the purposes of "suction." The kiln room is three stair steps elevated from the office and there's a lot of random stuff in both rooms that therefore blunts the directness of the box fan's wind. 

[MochiFriend]

OMG, I just went downstairs to turn off one of the 2 box fans, and @Bill Kielb, your suggestions seem to have made a change. THANK YOU! 

1) The office room smelled (understandably) like trash because the kiln room's smelliness was being sucked out via the fans. Now it smells like nice clean outside air.

2) The kiln room actually seems to smell better. 

I'm now in the last hour of my firing (~1800F), so obviously the smelliest part passed 8 hours ago, but there still was a lot of lingering smell from before. I'm interested to see if my glaze firing next Friday has a difference, and I'll also incorporate measurements from a particle reader here. I'll also call Skutt next week to get their advice on widening the bottom kiln hole a bit. I hope that this thread doesn't get archived in the next week.

I might be not understanding the whole concept of pressurization, but to my understanding some people have their kilns indoors next to a giant sliding door, outside in a shed, outside under an awning, etc. Isn't that a lot more pressurization on the kiln itself (thus perhaps affecting the firing schedule even?) than a box fan that's like 7 ft away, pointed 90 degrees away at the adjacent wall? 

I APPRECIATE YOU GUYS!!! 

[Bill Kielb]

1 minute ago, MochiFriend said:

The other one is helpful I think to still have in the office for the purposes of "suction." The kiln room is three stair steps elevated from the office and there's a lot of random stuff in both rooms that therefore blunts the directness of the box fan's wind. 

It really likely is not. We only think in terms of pressure.. To approximate that box fan is probably 150 cfm. The kiln exhaust is 10 cfm. You will be pressurizing all rooms to 140 cfm. Your kiln room will not really be negative and will become pressurized and remix with the office air. So the additional fan will dilute the office and  kiln room which is helpful but also encourage leakage to all other rooms adjacent. More exhaust in the kiln room than supplied is how we make this negative. Ducting through the crawl space could be a neat solution.

[Bill Kielb]

12 minutes ago, MochiFriend said:

might be not understanding the whole concept of pressurization, but to my understanding some people have their kilns indoors next to a giant sliding door, outside in a shed, outside under an awning, etc. Isn't that a lot more pressurization on the kiln itself (thus perhaps affecting the firing schedule even?) than a box fan that's like 7 ft away, pointed 90 degrees away at the adjacent wall? 

No, if your kiln is outside then it’s already ventilated with outdoor air, so just open the door to the shed. We just want to suck more air out of the kiln room than we put into the adjacent rooms to do this correctly. The small kiln vent likely will not be enough to do this and again if it sucks too much air through the kiln, your kiln may not have enough power to fire so drilling more or larger holes has a downside.  If your going to blow some air in, use your smallest fan on the lowest setting at the farthest window in hopes of being slightly less than the kiln vent while getting some dilution air into the office.

Edited December 2, 2023 by Bill Kielb

[MochiFriend]

O

18 minutes ago, Bill Kielb said:

It really likely is not. We only think in terms of pressure.. To approximate that box fan is probably 150 cfm. The kiln exhaust is 10 cfm. You will be pressurizing all rooms to 140 cfm. Your kiln room will not really be negative and will become pressurized and remix with the office air. So the additional fan will dilute the office and  kiln room which is helpful but also encourage leakage to all other rooms adjacent. More exhaust in the kiln room than supplied is how we make this negative. Ducting through the crawl space could be a neat solution.

Got it. I did just check and the Skutt Envirovent is 140cfm (https://skutt.com/images/11.18-EnviroVent-2-Specifications.pdf). However I've turned off the box fan anyway. 

Will look into ducting / fan via the crawl space! I also just want to exhaust (haha get it?) all other options as well since I'll coordinate with our handyman in for that, hence why I'm curious about the kiln hole size possibility. 

Thanks Bill, really appreciate your taking the time out of your evening to trouble shoot all of this too!

[Bill Kielb]

4 minutes ago, MochiFriend said:

Got it. I did just check and the Skutt Envirovent is 140cfm (https://skutt.com/images/11.18-EnviroVent-2-Specifications.pdf). However I've turned off the box fan anyway. 

 

I have measured these in operation, with all the small diameters and restrictions they do not flow more than 20 cfm. It’s rated 140 cfm in free air. Configured as downdraft it does not exhaust nearly that much. Old video here but measured from two kilns was less than 20cfm. https://youtu.be/etpa2Pc9Hug?feature=shared

 

[neilestrick]

@MochiFriendKilns the size of yours often seal better than bigger kilns, so the air flow can be restricted. My smaller kiln tended to smell a bunch, too. Before opening up the hole in the bottom, add another hole to the lid. If that doesn't help then add another small hole to the bottom rather than make it larger. That way you can plug it if there's a negative outcome from doing that. Another thing you can try is blocking one of the intake holes in the vent cup under the kiln so it will have more pull from the kiln.

All kilns will smell during wax burnout, around 500-800F degrees. It's unavoidable. There's just too much burning out for the downdraft to deal with.

One thing I've done for a couple of customers and in my own studio is to install a duct fan near the kiln, like THIS ONE. You would need to make a 6" hole through the wall for it and put a 6" cap on the outside just like a dryer vent. You can hang it near the kiln and connect it to the hole with a flexible duct. Keep the window cracked in the neighboring room for makeup air. At up 400cfm it'll help pull out any extra fumes and heat. Plus it's cheap.

[MochiFriend]

6 hours ago, neilestrick said:

One thing I've done for a couple of customers and in my own studio is to install a duct fan near the kiln, like THIS ONE. You would need to make a 6" hole through the wall for it and put a 6" cap on the outside just like a dryer vent. You can hang it near the kiln and connect it to the hole with a flexible duct. Keep the window cracked in the neighboring room for makeup air. At up 400cfm it'll help pull out any extra fumes and heat. Plus it's cheap.

Ah, you raise some very good and logical points. For this fan - which is similar to Bill's bathroom fan idea, thanks for the link! - two quick questions:
1) Could I potentially install the fan in the wall, then connect the duct to the duct on my kiln vent (between the Envirovent motor and the hole in the wall)? Essentially I'm trying to limit the number of holes I drill on the external wall of my house, lol. Crazy idea? 
2) In your experience, does this fan hold up to the 35db noise estimate that it's marketed as? Just trying to be considerate to neighbors on the other side of the fence.
 

6 hours ago, neilestrick said:

Before opening up the hole in the bottom, add another hole to the lid. If that doesn't help then add another small hole to the bottom rather than make it larger. That way you can plug it if there's a negative outcome from doing that. Another thing you can try is blocking one of the intake holes in the vent cup under the kiln so it will have more pull from the kiln.

I really appreciate this advice. Is it somewhat contradictory to create a hole in the lid as a start, and then to try to plug up one of the lid holes as a follow-up experiment? Plus, if the issue is that the vent is not drawing enough air thru the bottom wouldn't the former (creating an additional hole in the top) exacerbate the problem because more of the warm air would escape thru the lid? Thanks very much. I've read a lot of these forums as a lurker and have learned quite a lot from your past advice too. 

Hope you are all having a nice weekend~!

[Mark C.]

Read about make up air-when you suck air out air needs to come in-called makeup air-you need makeup air in a small space

[neilestrick]

3 hours ago, MochiFriend said:

1) Could I potentially install the fan in the wall, then connect the duct to the duct on my kiln vent (between the Envirovent motor and the hole in the wall)? Essentially I'm trying to limit the number of holes I drill on the external wall of my house, lol. Crazy idea? 

No, you don't want this additional vent on the same duct line as the vent, as it will affect the draw of the kiln vent. The fan I linked to needs a 6" duct and the Envirovent needs a 4" duct, so if you wanted only one hole in the wall you could do a single 8" hole and use a Y duct that splits into a 6" and 4". Another option would be the 4" version of the vent, which would allow for a single 6" hole that splits into two 4" ducts. The 4" version has 1/2 the power of the 6" though.

3 hours ago, MochiFriend said:

2) In your experience, does this fan hold up to the 35db noise estimate that it's marketed as? Just trying to be considerate to neighbors on the other side of the fence.

The one I have in my shop is fairly quiet, but I don't know the actual db output. If you had a couple feet of flex duct between the motor and the hole that may help to dampen the noise.

3 hours ago, MochiFriend said:

Is it somewhat contradictory to create a hole in the lid as a start, and then to try to plug up one of the lid holes as a follow-up experiment?

Not plug the lid hole, but cover one of the holes in the cup under the kiln.  

[Bill Kielb]

1 hour ago, neilestrick said:

No, you don't want this additional vent on the same duct line as the vent, as it will affect the draw of the kiln vent. The fan I linked to needs a 6" duct and the Envirovent needs a 4" duct, so if you wanted only one hole in the wall you could do a single 8" hole and use a Y duct that splits into a 6" and 4". Another option would be the 4" version of the vent, which would allow for a single 6" hole that splits into two 4" ducts. The 4" version has 1/2 the power of the 6" though.

Just a quick mention
Neil makes a good point and without looking closer 8” combined is likely fine. Just a caution, while not the best it would be most correct to install backdraft dampers when combining exhausts so when one fan is not in operation the other will not have a short circuit path.
 

Actually just best to run them out independently as designed. 200 cfm in 6” round is over 1000 fpm which is significant. This is not worth calculating really and to do so is a bit complicated and requires actual airflows. Separate discharges most goof proof solution.

 

[Bill Kielb]

1 hour ago, neilestrick said:

The one I have in my shop is fairly quiet, but I don't know the actual db output. If you had a couple feet of flex duct between the motor and the hole that may help to dampen the noise.

You might be interested in AC infinity. I have had them installed in several kiln rooms and model dependent they come with a temperature controller which varies the speed as required. Very quiet fans for the most part at what I think are reasonable cost. Google Ac Infinity.

[MochiFriend]

Hi @Bill Kielb and @neilestrick, thank you both so very much for your thoughts!! 

I will attempt to use this fan on my next glaze firing. Do you think it would be less effective if: 1) I did not mount the fan to the wall, instead securing it to a shelf adjacent to the kiln — and 2) also ran ducting from the fan out one of the two windows in the nearby room? (I have a cover that can cover the entirety of the window except for a hole for the vent). Below is a diagram illustrating this. 

The reason why is because I'd like a quick, low-commitment way to test this fan option without putting multiple holes in drywall + my external wall. Totally get that this is just part of having infrastructure to support a kiln, but another option I am considering is moving the kiln into the office room to be between the two windows. This is a much larger endeavor, as we'd have to swap rooms in the house and move a lot of things around, so I want to test out the fan option first in an easy way. If it does seem effective, then I could commit to installing it w/ proper venting and such. 

Below is a diagram of the potential new kiln placement. I believe this would be better(?) as the two windows naturally would create a negative pressure situation around the kiln, though it might be more annoying to have the kiln right next to the window — perhaps that might affect the firing? 

As always, I really appreciate your time and insights. Thank you! 

[MochiFriend]

3 minutes ago, Bill Kielb said:

AC infinity

thank you!! this looks great! 

[Bill Kielb]

10 minutes ago, MochiFriend said:

2) also ran ducting from the fan out one of the two windows in the nearby room? (I have a cover that can cover the entirety of the window except for a hole for the vent). Below is a diagram illustrating this. 

This will work, mounting the fan on the board to directly discharge, then run the duct in the crawl or wherever. With the fan mounted at the window all the rest of will be negative pressure, so no worries of small leaks. This is traditionally how we treat exhaust duct in general to guarantee no exhaust leaks out of the duct.

Edited December 3, 2023 by Bill Kielb

[Bill Kielb]

16 minutes ago, MochiFriend said:

thank you!! this looks great! 

Make sure you pick the right model and control. The picture shows three different applications. You likely want the 6” round with the outdoor louvers. Airlift air shutter series

Edited December 3, 2023 by Bill Kielb