Question on vent management

MitchS

New member
I got my 18" WSM a bit over a year ago and have had some okay sessions. The one thing I'm still confused on is how to properly manage the heat using the vents at the bottom and top. There's a relationship between the bottom and top I'm just getting. So far I've gotten lucky but would like to understand them a bit more. I have a couple of questions:

1) What is the relationship between the bottom vents and the top vent? If I leave the bottom vents at about 1/2 way, can I simply manage the heat by the top vent only?
2) I assume less air (closed vents) means cooler temps. Yes? I know this is a pretty basic question, but I've gotten so many weird behaviors that I have to ask. Sometimes when I think I'm going to bring the temp down, it just keeps going up.
3) What is the heat's 'momentum'? In other words, if I have a target temp of 225 and the vents are pretty open to bring it to temp, when should I start closing them so I don't overshoot it by too much? (assuming closing them brings down the temp)

Thanks in advance. I know these are pretty basic, but as I said earlier, it's been hit/miss with my sessions and I would like to understand the vents a bit more if possible.
 

Jim C in Denver

TVWBB Super Fan
Most folks regulate temps just with the bottom vents. Exception being if the cooker is really running away hot and needs to be seriously choked off.

I find it easiest to adjust the bottom vents one at a time. That’s what Harry Soo recommends.

Once I get to about 200F, I close two vents completely. I fiddle with the one remaining vent until it settles in. I usually go for the first 6-8 hours with just one bottom vent open (full or partial). As the cook progresses, I start opening vent 2 if the temp drops. Then later vent 3. Top vent always stays open (absent a heat spike).
 
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Chris Allingham

Administrator
Staff member
Mitch,

I would suggest that you visit my website virtualweberbullet.com, go into the Cooking Topics section, and browse some of the articles. In almost every case (skip the first four "Beginner" recipes, they don't depend on vent settings), I describe how I set the vents for each cook and I show a table of how I set the vents top and bottom. The table is not meant to be a prescription for exactly how you should set your vents, rather just an example of what happened and what I did for my cook. Your experience may vary.

But the one constant in almost all situations is that I leave the top vent 100% open throughout a cooking session and use the bottom vents to adjust temperature. I think of the bottom vents as the air intake to the engine, the charcoal as the fuel that runs the engine, and the top vent as the exhaust pipe. Only in very rare cases would I ever partially close the top vent during cooking, like when my cooker gets so hot that closing all bottom vents won't bring it down to my target temp...then I may partially close the top vent. I can count on less than the fingers on one hand the number of times I've done that in 23 years of cooking with the WSM.

Yes, less air into the cooker = lower temps. You want to manage the temperature on the way up and not let it get out of control. It can be harder to bring down once it gets higher than you want. In addition to vent management, another way to control this is by how you start your fire. Using the Minion Method to start a small fire that you manage carefully as it grows is a good way to keep temp under control. Also, cooking a large amount of cold meat helps keep cooker temp down...building a big fire then cooking half a chicken is a disaster in terms of temperature control.

If you close the top vent and all bottom vents, the fire should go out within 45-60 minutes. If it doesn't, you've got some poor fitting parts that are letting uncontrolled air into the cooker. You might experience this during cooking as difficulty in being able to get temp to drop when you partially close bottom vents...a topic for another post on another day and only if you have this problem.

In terms of "momentum", I describe this in each of my articles. For example, if I'm shooting for a range of 250-275*F, I will leave bottom vents wide open until 225*F and then start partially closing them to settle into my target range.

By the way, I simply eyeball the "percentage open". It's a round hole in the damper that covers a teardrop-shaped hole in the charcoal bowl, so it's an odd geometry. To me, if it looks like half the space is open, then I call it 50%. To me, it's just 0%, 25%, 50%, 75%, 100%. You'll get a feeling for it over time.
 
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ChristopherC

TVWBB Super Fan
I am a newbie (about 5-6 cooks so far) and I have found the WSM 18 pretty easy to control with some exceptions.

I am learning it is all about standards and slow adjustments. ie as you are learning use the same type of coal and setup, etc... and when you make changes don't just suddenly adjust all 3 vents, etc...

I always start with all vents open 100%. Then when the temp rises to about 200 I close 2 of the bottom vents half way and see if it slows down the rise. I try to always leave the bottom vent OPPOSITE the top vent open...just my thing - I am hoping the air comes in the bottom and moves across the smoker to the top vent thus moving thru the path of my meat. Not sure if it matters with the large distance, but that is how I roll.

I continue closing the 2 bottom vents I already started closing until my desired temp is locked in. If it rises more than 25d past my ideal temp, I start closing the 3rd bottom vent partially.

If things get really out of control, I take the lid off close all 3 bottom vents except the last one a sliver/crack. Then I put the lid back on...this usually works for me in "starting from scratch". Then I can do the reverse and open the bottom vent more and the other bottom vents if needed to increase the temp to my ideal.

I basically group my vents into 3 groups:

1) Top vent - almost always open 100%.

2) Bottom vent opposite side the top vent - usually open 100%...if not, the last one to start closing.

3) Bottom vents beside the top vent side - close and open together to lower and raise temps.


So far, this has worked very well for me and I find having water in the pan, the top vent open all the way and the opposite side bottom vent open all the way gets me pretty close to 225-275 all the time and usually close to 250. If not, usually I am running out of charcoal.
 

MitchS

New member
This is really helpful. Thank you! I'm going to give this a shot this weekend with a rack of pork ribs and see it temp management is easier.

Thanks again!
 

MitchS

New member
Noticing how many new WSM users are opening and even removing the lid when the pit temperature is high and out of control.
Doing so is entirely the reverse of what you need to do.
Opening the lid gives the coals a huge dose of oxygen, thereby increasing the coals burn rate and temperature output.
This made me smile. I did this exact thing this weekend. Felt like an idiot having to babysit the smoker every minute to manage the temp. Luckily it was the last 30-minutes and it wasn't very impactful. :)
 

Lynn Dollar

TVWBB Wizard
I bought my first WSM in 2002 after finding this site ( I lurked here for 15 years before beginning to post ) and way back then, someone made a post about using dowel rods to measure the opening of each vent. Its sort've nerdy but it helped me a lot. I'm sure the post from the person who did the math, is still in the archive.

And I built this and still use it , the numbers are the % of vent opening for each diameter of dowel rod.

20200909_082022_resized.jpg
 

MitchS

New member
I bought my first WSM in 2002 after finding this site ( I lurked here for 15 years before beginning to post ) and way back then, someone made a post about using dowel rods to measure the opening of each vent. Its sort've nerdy but it helped me a lot. I'm sure the post from the person who did the math, is still in the archive.

And I built this and still use it , the numbers are the % of vent opening for each diameter of dowel rod.

View attachment 13763
Ha! That is 'nerdy' but I'm totally down with that. what a great idea :)
 

Jim C in Denver

TVWBB Super Fan
Wow -- that's very comprehensive.

For the smallest opening, I use a skewer/big toothpick. Next smallest is pencil or metal straw.

After that I eyeball/free hand it.
 
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MitchS

New member
Mitch,

I would suggest that you visit my website virtualweberbullet.com, go into the Cooking Topics section, and browse some of the articles. In almost every case (skip the first four "Beginner" recipes, they don't depend on vent settings), I describe how I set the vents for each cook and I show a table of how I set the vents top and bottom. The table is not meant to be a prescription for exactly how you should set your vents, rather just an example of what happened and what I did for my cook. Your experience may vary.

But the one constant in almost all situations is that I leave the top vent 100% open throughout a cooking session and use the bottom vents to adjust temperature. I think of the bottom vents as the air intake to the engine, the charcoal as the fuel that runs the engine, and the top vent as the exhaust pipe. Only in very rare cases would I ever partially close the top vent during cooking, like when my cooker gets so hot that closing all bottom vents won't bring it down to my target temp...then I may partially close the top vent. I can count on less than the fingers on one hand the number of times I've done that in 23 years of cooking with the WSM.

Yes, less air into the cooker = lower temps. You want to manage the temperature on the way up and not let it get out of control. It can be harder to bring down once it gets higher than you want. In addition to vent management, another way to control this is by how you start your fire. Using the Minion Method to start a small fire that you manage carefully as it grows is a good way to keep temp under control. Also, cooking a large amount of cold meat helps keep cooker temp down...building a big fire then cooking half a chicken is a disaster in terms of temperature control.

If you close the top vent and all bottom vents, the fire should go out within 45-60 minutes. If it doesn't, you've got some poor fitting parts that are letting uncontrolled air into the cooker. You might experience this during cooking as difficulty in being able to get temp to drop when you partially close bottom vents...a topic for another post on another day and only if you have this problem.

In terms of "momentum", I describe this in each of my articles. For example, if I'm shooting for a range of 250-275*F, I will leave bottom vents wide open until 225*F and then start partially closing them to settle into my target range.

By the way, I simply eyeball the "percentage open". It's a round hole in the damper that covers a teardrop-shaped hole in the charcoal bowl, so it's an odd geometry. To me, if it looks like half the space is open, then I call it 50%. To me, it's just 0%, 25%, 50%, 75%, 100%. You'll get a feeling for it over time.
Super helpful. Thank you!
 

Jim C in Denver

TVWBB Super Fan
I think people lift the lid to lower the temperature on the cooking grate and save the brisket that is getting incinerated.

That does help the brisket in the moment. But it also stokes the fire, which compounds the problem.
 

ChristopherC

TVWBB Super Fan
Weird...but worked for me a couple of times so far. I thought exactly the same thing...if I open the lid aren’t the coals just gonna get hotter. But when I tried it the first time (was over 300 at top grate level) the temp lowered to 120 and after I replaced the lid the temps never got above 270. So tried it again another time and same thing. No idea why it worked nor the science behind it.

Noticing how many new WSM users are opening and even removing the lid when the pit temperature is high and out of control.
Doing so is entirely the reverse of what you need to do.
Opening the lid gives the coals a huge dose of oxygen, thereby increasing the coals burn rate and temperature output.
 

Chris Allingham

Administrator
Staff member
Wow, that thread features two of my old forum favorites, Rita Yeazel and the famous Jim Minion of the Minion Method. In fact, Rita was the one that had a dog named Weber.

But as much as I love Rita, I'm not going to carry around a series of dowels to set my vents. When lighting is bad, I use a flashlight or a work light to see what I'm doing. And the precision of vent settings is not important, after years of use you get a sense of what's your 50% setting, your 25% setting, etc. But what a fun thread to look back on, thanks for finding it!
 

Jim C in Denver

TVWBB Super Fan
No idea why it worked nor the science behind it.

Lifting the lid releases a lot of heat very quickly and lowers the top grate temperature. Because all that fresh outside air now hitting your food is 150 degrees (or more) cooler than the air inside the cooker.

Sure the fire gets stoked up with the extra oxygen. But when the lid goes back on, that stoked fire now has to reheat a cooled off cooker. Which takes a while.

But eventually, you have to crank the fire down which requires less oxygen.
 

Lynn Dollar

TVWBB Wizard
I like to have all three vents open the same amount. And it does not take much to increase air flow in a WSM. As everyone should know, they're purty persnickety .

I have a table on my patio for barbecue junk, and I keep my dowel rods there. Had them a long time.
 

Josh - CT

New member
I am a fairly new WSM owner as well and still learning. What I find interesting is that WSM owners seem to adjust the bottom vents and leave the top vent 100% open. When I watch videos on drum smokers (similar in design), the approach seems to be the opposite. While the bottom vent is adjusted (to 50%), it seems like they largely adjusting the top vent to get to their desired temperature. For example:
 

Jim C in Denver

TVWBB Super Fan
You can control the fire by adjusting the top vent. Search on here and you will see discussions of that topic which cite WSM champ Harry Soo as being in favor of adjusting at the top.

That discussion is where I got my preferred method (also from Harry) -- run the WSM with just one vent open on the bottom and the top open too. Then eventually start opening up #2. And then later start opening up #3. For me, it is easier to keep track of one at a time rather than all three at 1/4, then 1/2, then 3/4...

But the norm on here seems to be to adjust primarily with the bottom. Some folks say that adjusting via the top in some way messes with the flow of good smoke. On that, I have no idea. There's also chatter about how you'd use the top vent differently if you use an ATC.

And then there's this from the Weber website (mostly directed at kettles): "We suggest leaving the bottom dampers fully open and using the top lid damper to control the temperature." Could be that on a kettle, you might be more worried about falling ash clogging up the air flow of a slightly cracked bottom vent. So better to leave the bottom open and just adjust the top.

Could be that folks use the bottom for the WSM simply because there are three vents and so there's a lot more fine adjustments you can make. And ashes blocking the three WSM vents is not a worry.
 
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MichaelM

TVWBB Fan
My first few cooks were runaways... I have since started closing the lower vents around 180 - 190. I might be adding a bit more time to get up to target, but better than fighting to get back down to if I over shoot. I keep the back bottom vent closed, primarily because I can't reach and open it later in a long cook to get those 'reserve' coals lit. The front two are fully open until 180-ish and then I start closing them.

The top vent.. I visualize air flow as it being sucked up through the top vent. If I choke that down, it should reduce the amount of air being sucked in the bottom, But there are three bottom and one top (plus any leaks) so adjustments at the top vent are less impactful.

I just got a kettle after decades of cooking on a gasser (which I haven't used in a few months). I am trying to learn the kettle temp controls and found the vid's by Kettle Pitmaster very interesting.
 

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