Offset Damper vs. No Damper Experiment

[SkaterSmoker]

On my 1975 I've been getting great results running the pit with the stack wide open, and my door cracked an inch. However, I've noticed a lot of others use the damper, and there's been some recent guidance on why it's important (e.g. lower and slower, more smoke flavor, less crispy food with a gentler cooking environment/less convection).

My results with time stamps and settings are in the spreadsheets below. I'm more than excited I can run my pit in a "high convection mode" and a "lower & slower mode" depending on the stage of my cook or what I'm cooking. Isolating the hotspots in each mode was very helpful too.

A few notes:
-I tested all ThermoWorks probes before.
-I elevated the probes with foil in the effort to eliminate radiant heat from the grates, however the foil may have negated this.
-The 10 data points are at various stages of adding splits for a broader range of impact.
-With the damper closed, temperature spikes were minimal when adding a new split, vs. quite the opposite with the damper wide open, which makes sense since the damper slows down airflow.
-With the damper and slower airflow, I had to build bigger fires (1 extra split) to reach my target temps, which is due to the slower airflow and extra time the gasses have time to cool before reaching the cooking surface.

 

[4ever3]

Interesting, thanks for the test and info.

 

[Fooball]

Seems to be quite a bit hotter avg. temp with stack open. (too hot for me!)

Also, teltrue is way cooler than therms. Hard to believe location would make it that much cooler since your teltrue is nearly at grate level. Wonder why?

 

[SkaterSmoker]

Seems to be quite a bit hotter avg. temp with stack open. (too hot for me!)

Also, teltrue is way cooler than therms. Hard to believe location would make it that much cooler since your teltrue is nearly at grate level. Wonder why?

I should've clarified I wasn't trying to run the same temperature for each setting. First line my Tel Tru target was 225, Lines 2-5 target temp was 240, Lines 6-8 target temp was 275 (increased airflow as I switched to stack wide open), last two were 240 again. When I would switch from damper closed to damper wide open, the temp would spike because of the increased air flow. Whenever I'm running my pit with the stack wide open I can pretty much achieve any temp I want from 175 - 350. So, it's a preference of where you want the hot spot and how much convection you want.

The variance between Tel Tru's and probes is discussed quite a bit between WH owners. Another owner told me to use potatoes next time since the radiant heat from the foil impacts results. Also, the probes are instant and the Tel Tru's take some time to catch up. I know when Workhorse tested their pits they suspended 40+ probes to eliminate those impacts and per them the results matched the Tel Tru's.

 

[sudsandswine]

Interesting experiment. I was going to test out some different intake/exhaust damper settings on my Shirley the next time I fired it up. It seems to cook a bit differently with the round cook chamber compared to the cabinet door/flat box model I'd had previously. This one draws really hard, I can feel the air move through the chamber even with a door open. The leading edges on some briskets I was cooking started to get crispy and I had to foil the edges. Thought maybe slowing the air/convection down would help.

 

[SkaterSmoker]

Interesting experiment. I was going to test out some different intake/exhaust damper settings on my Shirley the next time I fired it up. It seems to cook a bit differently with the round cook chamber compared to the cabinet door/flat box model I'd had previously. This one draws really hard, I can feel the air move through the chamber even with a door open. The leading edges on some briskets I was cooking started to get crispy and I had to foil the edges. Thought maybe slowing the air/convection down would help.

It's really helpful to do this test. I wish I would've done it sooner and I've had my pit for 8 months. Similar to you, the point end of my briskets were getting a little crispy too early and I would have to use foil to cap it or rotate earlier than I wanted. Now I know why. I can't wait to cook my next one.

 

[Connor_Macleod]

This is excellent data! A few questions/observations:

1) Would the results have looked the same if you ran the firebox door 1" open for both damper cases (wide open and 2/3 closed)? I wonder whether the firebox door is the limiting factor for the airflow in the damper closed case, or if the air flow would be the same whether the door was open 1" or 2".

2) That's fascinating to see the hot spot move due to the changing damper position. This is consistent with my experience cooking on my offset where restricting the airflow pushes the hot spot closer to the firebox since the draw is not sucking the hot air far into the cook chamber before it has a chance to rise.

3) Re: Fooball's question above, that is quite a temperature differential...hopefully Workhorse owners take that into account during their cooks. Maybe that happens because the Tel-Tru probe is so close to the cook chamber wall, which absorbs heat out of the air in the cook chamber, resulting in the temperature in the middle of the chamber being significantly higher than that near the wall?

 

[SmittyJonz]

Now do the same Tests while loaded with meat(s)

 

[sudsandswine]

Now do the same Tests while loaded with meat(s)

Also an interesting point - my last Shirley evened out in temps right to left when fully loaded with meat. I felt like it ran quite a bit better than when it'd have just one or two things in it.

 

[SkaterSmoker]

This is excellent data! A few questions/observations:

1) Would the results have looked the same if you ran the firebox door 1" open for both damper cases (wide open and 2/3 closed)? I wonder whether the firebox door is the limiting factor for the airflow in the damper closed case, or if the air flow would be the same whether the door was open 1" or 2".

2) That's fascinating to see the hot spot move due to the changing damper position. This is consistent with my experience cooking on my offset where restricting the airflow pushes the hot spot closer to the firebox since the draw is not sucking the hot air far into the cook chamber before it has a chance to rise.

3) Re: Fooball's question above, that is quite a temperature differential...hopefully Workhorse owners take that into account during their cooks. Maybe that happens because the Tel-Tru probe is so close to the cook chamber wall, which absorbs heat out of the air in the cook chamber, resulting in the temperature in the middle of the chamber being significantly higher than that near the wall?

1) With the damper closed, I did adjust the door from 1-3 inches and it had little impact on temps, just smoke.

2) If you look at enough 1975 owners photos, there's always a white spot in probe #2 location where the hot air comes to grate level, so my hope was using the damper would move that spot closer to the firebox, and it did that just as you experienced.

3) There's a lot of WH owners in a private group who've tested it. The one guy who used potatoes to eliminate radiant heat from the probe holder and grate, and waited for the timing element, got his to measure up almost exactly the same. Most other owners who've done the test at grate level, get about 20 degree difference.

Others and I have also tested temps from front to back, and they're dead on even.

Based on all the cooks I've done, I believe the Tel Tru's are close to the actual temp based on cook times. My brisket cooks for similar size briskets are taking the same amount of time as people using Millscales, Fatstacks, 250s, Franklin's, etc. A trimmed 10-12lb brisket cooked around 250, then bumped up to 275 the last 4 hours takes about 13 hours on average. Spare ribs cooked around 250 take about 5-6 hours.

 

[SkaterSmoker]

Now do the same Tests while loaded with meat(s)

Yes, good point and that's next on my list. I've only typically cooked with the stack wide open as many other 1975 owners, and there's always a white spot in probe #2 location where the air meets grate level. So, the numbers were no surprise to me where the hot spot was with the stack wide open. But yes, doing the test with the typical amount of food and placement in the pit is very important as well.

 

[SkaterSmoker]

This is excellent data! A few questions/observations:

3) Re: Fooball's question above, that is quite a temperature differential...hopefully Workhorse owners take that into account during their cooks. Maybe that happens because the Tel-Tru probe is so close to the cook chamber wall, which absorbs heat out of the air in the cook chamber, resulting in the temperature in the middle of the chamber being significantly higher than that near the wall?

Also, in this test my main focus wasn't on the Tel Tru vs. Probe readings, but the left to right temps and hot spot. I quickly made those foil holders and really didn't think that part out. In the past, I've lined up 3 probes front to back directly in line with the Tel Tru's and all three probes are even and about 20 degree different from the Tel Tru. I'll need to re-test that as well.

 

[Connor_Macleod]

...In the past, I've lined up 3 probes front to back directly in line with the Tel Tru's and all three probes are even and about 20 degree different from the Tel Tru. I'll need to re-test that as well.

That's great that you're doing all these tests. Hopefully this will inspire me to do more testing on my own smoker...I was thinking about re-running the biscuit test on mine or probe testing under different scenarios (e.g., water pan vs. none, damper position, door position, blocking log, etc.) now that I have more experience operating it.

Another question: Have any of the Workhorse owners attempted to measure the volumetric flow rate of the air through their cookers? I have often wondered whether the airflow flux (i.e., volumetric air flow rate divided by cross-sectional area perpendicular to the direction of flow) might be a key parameter if one was trying to design a backyard smoker with the same performance characteristics as a big 1,000-gallon smoker.

 

[Fooball]

Another question: Have any of the Workhorse owners attempted to measure the volumetric flow rate of the air through their cookers? I have often wondered whether the airflow flux (i.e., volumetric air flow rate divided by cross-sectional area perpendicular to the direction of flow) might be a key parameter if one was trying to design a backyard smoker with the same performance characteristics as a big 1,000-gallon smoker.

I watched a youtube video on this where a guy kept adding extensions to the stack and used a small hand held air speed measuring device to measure speed coming out of the stack.

By the time he was done with the experiment the stack was like 10' tall. Ha!

He melted the little plastic fan on his instrument holding it over the stack output.

OH!....here it is. I found it:

https://www.youtube.com/watch?v=n4VxtqcYiOQ

 

[sandro]

I love this, it's great to see some data on different offsets than mine, thanks a ton for running this experiment! I feel the Tel-Tru is reading lower temps because it's sitting on the door, that side runs much cooler than opposite to the door, which is why you might want to rotate your briskets slightly to have the thicker side to the wall

I love the way Workhorse pits are engineered, I like to think JD and the folks put the rightmost Tel-Tru so close to the firebox because they knew the way they had designed the exchange would push the hot spot away from the thermometer, and that gave people the peace of mind that the chamber was cooking within 5 degrees. Temps are just guidelines anyway, and I'm sure this little trick made BBQ more enjoyable for a ton of people

 

[SkaterSmoker]

I love this, it's great to see some data on different offsets than mine, thanks a ton for running this experiment! I feel the Tel-Tru is reading lower temps because it's sitting on the door, that side runs much cooler than opposite to the door, which is why you might want to rotate your briskets slightly to have the thicker side to the wall

I love the way Workhorse pits are engineered, I like to think JD and the folks put the rightmost Tel-Tru so close to the firebox because they knew the way they had designed the exchange would push the hot spot away from the thermometer, and that gave people the peace of mind that the chamber was cooking within 5 degrees. Temps are just guidelines anyway, and I'm sure this little trick made BBQ more enjoyable for a ton of people

You're welcome! I'm interested in the design element too. I'm in a private group that JD is a part of, and he's very gracious and doesn't criticize results like these I share. It's pretty complex stuff to describe or market to a new user (i.e. fire management is an acquired skill, not like pushing a button), so I can see if that's why he simplified it.

I believe this pit is engineered in way that's incredibly versatile - you can run it with a ton of convection for extra rendering or crisping up chicken, or you can use the damper and get that low and slow.

I've cooked 8 briskets in the last 6 weeks trying to perfect my technique, and I always take 3,6, and 8 hour progress photos. I can't wait to cook my next few with the damper technique and compare results.

 

[SkaterSmoker]

That's great that you're doing all these tests. Hopefully this will inspire me to do more testing on my own smoker...I was thinking about re-running the biscuit test on mine or probe testing under different scenarios (e.g., water pan vs. none, damper position, door position, blocking log, etc.) now that I have more experience operating it.

Another question: Have any of the Workhorse owners attempted to measure the volumetric flow rate of the air through their cookers? I have often wondered whether the airflow flux (i.e., volumetric air flow rate divided by cross-sectional area perpendicular to the direction of flow) might be a key parameter if one was trying to design a backyard smoker with the same performance characteristics as a big 1,000-gallon smoker.

I don't believe anyone has, but that is a very interesting idea!

 

[gtsum]

Looks good. I’ve had my 1975 for about 15 months and have found similar. If I am running a lazy fire (smaller flames, damper closed a bit to slow it down), I can get my tel trus to within 10 degrees of my ThermoWorks digital probes. When running more airflow through the cooker and more violent flames, that’s when I’ve seen larger differences between the door therms and the digital ones.


Sent from my iPhone using Tapatalk Pro

 

[SkaterSmoker]

Looks good. I’ve had my 1975 for about 15 months and have found similar. If I am running a lazy fire (smaller flames, damper closed a bit to slow it down), I can get my tel trus to within 10 degrees of my ThermoWorks digital probes. When running more airflow through the cooker and more violent flames, that’s when I’ve seen larger differences between the door therms and the digital ones.


Sent from my iPhone using Tapatalk Pro

Very interesting. This seems to support what I've heard from others regarding a high amount of airflow can falsely impact the probe readings in that environment.

 

[Connor_Macleod]

I watched a youtube video on this where a guy kept adding extensions to the stack and used a small hand held air speed measuring device to measure speed coming out of the stack.

By the time he was done with the experiment the stack was like 10' tall. Ha!

He melted the little plastic fan on his instrument holding it over the stack output.

OH!....here it is. I found it:

https://www.youtube.com/watch?v=n4VxtqcYiOQ

Nice find! From those flow velocity calculations, he could calculate the air flow flux through the cook chamber. I would be very interested to see how the air flow flux values in the cook chamber compare for that guy's Oklahoma Joe smoker vs. a Workhorse and vs. a big 1,000-gal Moberg.