Newbie self builder reverse flow, two cooks, two fails.

[Blondy_UK]

Wow, thats a lot of response and some good sugestions.

I will try to add some more info, the wood had been gathering dust in my shed for probably 3-4 years which went onto a chimney full of glowing coals and left it to burn down and for the cook chamber to get hot before putting in the meat. At that first time i only had dial meat probe which i left on the shelf so not that accurate. I have a twin probe wireless thing now but did not arrive untill the day after my second cook.

I did look at a calculator regarding the dimensions and such and it recomended a 6 1/2" tall chimney. When i built it i thought that a larger stack would get the smoke out quicker and being that high would keep the wood smoke out of my face and off of my clothes. I think i will do another dry run and probe the chimney at different levels just to see whats going on there before i get the hacksaw out, but if thats going to help then it will have to be done.

The space at the end of the RF baffle plate is comparable with the opening to the firebox/ cook chamber ang bigger in area than the stack, i did cut a piece plate to close it of a bit as i read somewhere that it could be putting too much smoke into the cook chamber and not being able to leave quick enough.

I was getting the TBS a lot of the time but it was when i was adding wood the keep the temp up i was getting some white smoke . So was wondering if its possible to do long cooks on wood but as one of the coments said the can do 10-12 hours without wrapping. Thats what i'm after.

There are some picks on my welcome call page also whats OP mean?
I hope i have given all the extra info, there were a lot of suggestions to try but if i have missed any replys out let me know and i wil try to give more info but thanks again for all of your suggestions. Weather permitting i will be burning again at the weekend. PJ

 

[SmoothBoarBBQ]

Blondy_UK,

OP means "Original Poster" so in this instance you're the OP. I certainly believe the culprit is the excessively long and large diameter smoke stack. I agree that you should probe it and if the air coming out isn't very hot then you should go with your instinct and cut it down quite a bit. You say you think 6.5" is what your calculations gave you and that sounds pretty good, though I'm not sure if you need to go quite that low to start. Maybe cut it down a bit, do a burn and see what's going on.

Thin Blue Smoke (TBS) is ideal but you will get a bit of white smoke when you put a new log on the fire. This is nothing to worry about when the airflow is good, so I believe once you make some adjustments you'll see that white smoke will come and go very quickly. Something to think about while you're messing around with the smoke stack and what not is to put a few balls of foil (just sheet foil balled up) in a few different places on your cooking grate, just like you would meat. Those balls of foil should be very clean after a long smoking session... if they are black then you know you're still having serious airflow issues. If they are slightly dark that's probably OK, but you're looking for them to look VERY clean, almost as clean as when you pulled them off the foil roll. This way you can see what's really happening in your cooking chamber while you're working on your exhaust stack adjustments without wasting good pieces of meat.

The biggest thing about an offset cooker is that you can get that TBS and keep a super clean fire for a very long cook. On my new reverse flow offset smoker I run a very clean fire and I will leave an entire brisket on there for 12+ hours and it comes out with just a nice kiss of smoke. Proper airflow does that for you so the smoke is just kissing your meat as it is pulled gently through the smoking chamber. So this is what you're talking about with a long cook without wrapping and for that to happen you really need good airflow.

I hope I helped you out a bit but I'm very glad you've crunched some numbers and realize your exhaust stack is likely your issue. Post updates as you move forward and I'm pretty curious about the temps you're going to get in that exhaust stack as well. If you desire keep us posted, and good luck! I certainly hope you can make this the cooker you wanted it to be. Cheers!

 

[m-fine]

A restriction on the reverse flow is not going to help at all. At this point you want to maximize airflow and avoid any restrictions.

I will repeat it again. Shorter chimney = LESS DRAFT!

The problem is either insufficient fire or not enough draft. Cutting the chimney is only going to make things worse. If you guys want to put your money where your mouth is, I will add 10-12 feet of additional chimney pipe to my Lang and demonstrate that the smoke will not cool off and fall back into the cook chamber. Raise $1000 to bet against me and I'll give you 2:1 odds. Word of warning, my degree in aerospace engineering comes from a real acredited university. I learned thermodynamics and fluid dynamics from text books and professors, not Internet forums. You will lose.

For the OP, build a bigger fire and see if it will burn clean. If not, post the dimensions of your openings, and pictures of your fire. Also what temperatures you are seeing. If the wood is 3+ years old and your fire has a sufficient coal bed, I am concerned that the firebox exit and RF are too small. Also, space in the firebox may be an issue.

 

[Kmm]

After looking at your pics, I am seeing something different. The height of what appears to be your intake/ clean out pipe is below your fire grate. There is another pic showing some unburnt wood on the far end of the firebox. Look closely at that same pic and you will see the ash clean out is nearly full. My suspicion is that puppy is drafting just fine.....perhaps too well such that it is pulling ash out of the fire box into the smoking chamber. I suspect you will need to find a way of bringing air in over the top of the ash bin so it creates a dead air space below the fire grate. Ash could well be responsible for the bitter taste that is rendering your meat to the dust bin.
Some are going to argue that their air intakes are below the fire grates and they don't have any problems....however, I'll bet they have more room between the bottom of the fire grate and floor of the ash bin which keeps the ash from choking the fresh air.

 

[Yellowhair42]

BTW, Feldon is complete bunk.

Why is that? Is there one better?

 

[pjtexas1]

After looking at your pics, I am seeing something different. The height of what appears to be your intake/ clean out pipe is below your fire grate. There is another pic showing some unburnt wood on the far end of the firebox. Look closely at that same pic and you will see the ash clean out is nearly full. My suspicion is that puppy is drafting just fine.....perhaps too well such that it is pulling ash out of the fire box into the smoking chamber. I suspect you will need to find a way of bringing air in over the top of the ash bin so it creates a dead air space below the fire grate. Ash could well be responsible for the bitter taste that is rendering your meat to the dust bin.
Some are going to argue that their air intakes are below the fire grates and they don't have any problems....however, I'll bet they have more room between the bottom of the fire grate and floor of the ash bin which keeps the ash from choking the fresh air.

^^^let's run with theory for a second...
on my rf if the wind is blowing too hard into the intake it will definitely pull ash under the rf plate and into the cook chamber. i wonder if the op has tried choking down the exhaust to slow down the air flow? i also wonder if the op can see ash blowing thru the cook chamber if he opens the cook chamber door? i sure can and that's how i figured out that i need to block off the wind from blowing into my intake on windy days. example: at the spring bash we spun my cooker around and away from the wind. the other 2 stick burners there did not have to do this. my rf pulls hard and the wind is not my friend.

the other thing mentioned is the space below the fire grate. i would get that raised up higher just to give the fire more room to breathe. i know franklin runs his cookers with no fire grate but i would try it anyway.

 

[SmittyJonz]

Maybe......Nuttins wrong with it and OP just Don't like Smoked meat........
He could try a pellet smoker.

Do some video of your next cook.

 

[Smilerb]

Welcome to a great site, looking at your photos, especially the one showing unburnt wood and charcoal in your fire box seems to me to indicate a fire management problem. I agree with what has been said before. I would raise the height of the fire grate. I would guess that air from your intake is passing over the top of your fire into the cooking chamber and really it’s a case of getting air to flow through the fire which is one reason a UDS are so efficient. I would try raising the height of the grate and also moving the fire away slightly from the transfer port to the cooking chamber.
When I was testing my recent build , I started with all briquettes because they are quite predictable, after 7 hours all ash nothing else left , my next run was a mix of briquettes and lump wood, again just ash left but not such a long burn but I did find adding lump wood created white smoke but a couple of minutes with the fire box open when I added new wood sorted that out, next will be all wood so a definite case of learning to control the fire before getting into some serious smoking.

 

[m-fine]

Why is that? Is there one better?

I have not seen a good one yet, wish there was one I could point people to.

The problem with Feldon is it uses the wrong inputs. The calculations are based on volume and ignore surface area, R/K value of the material, and other factors that will more directly drive BTU and airflow requirements. Much of it looks like it was developed by looking at a few designs that worked and trying to come up with some formulas, rather than actual engineering calculations as it is purported to be. The formulas will result in a smoker that works within certain size and shape ranges, but they will not scale well outside of those (undefined) ranges. It also does nothing for you in reverse. Many designs that violate the Feldon ratios work very well, and the calculator will not find the problem(s) with a design that does not work.

 

[JackW]

"the chimney extends down to the cooking rack" If so there can't be much room between the bottom of the stack and the top of the reverse flow plate. Maybe that is causing a backup of smoke in the cook chamber. My stack does not extend into the cook chamber at all. All in all agood discussion,

Jack

 

[m-fine]

"the chimney extends down to the cooking rack" If so there can't be much room between the bottom of the stack and the top of the reverse flow plate. Maybe that is causing a backup of smoke in the cook chamber. My stack does not extend into the cook chamber at all. All in all agood discussion,

Jack

Good catch. That could definitely cause problems.

 

[BurntOffering]

So in one of your pictures I see fire in your cooking chamber.
Is there a baffle plate in there?

 

[pjtexas1]

"the chimney extends down to the cooking rack" If so there can't be much room between the bottom of the stack and the top of the reverse flow plate. Maybe that is causing a backup of smoke in the cook chamber. My stack does not extend into the cook chamber at all. All in all agood discussion,

Jack

i had to go back and look...totally missed that. :tsk:

 

[weave1499]

void

 

[sleebus.jones]

I think what's happening here is that everyone talks about TBS, but newbies to this hobby haven't seen it. A picture is worth a thousand words, so a video must be priceless...

(this is not my video)

[ame="https://www.youtube.com/watch?v=w4M0HD8afTU"]Blue Smoke - YouTube[/ame]

So, if you see smoke bellowing continuously out of the chimney, you ain't got TBS.

 

[m-fine]

Yep, smoke out of a stick burner running cleanly should be nearly invisible as it is exiting the stack.

I am thinking if the OP built a fire and showed us some pictures or even a video it would be helpful. What does the fire and coal bed look like? What does the smoke coming out of the chimney look like? What happens when the cook chamber is opened? How far into the smoker does the chimney extend? What do the splits look like and how big are they?

 

[Blondy_UK]

Again, lots of replies and ideas. There is no baffle plate under the RF plate by the opening from the fire box. The chimney goes down to the cooking grate as in the picture but it is cut at an angle, i could easily take some out with a grinder if that would help. I have also see other cookers with an extra air inlet
vent higher up above the height of the coal grate which i can also put in without too much hassle. The TBS i was referring to was more of a clear heat haze coming from the chimney but at times it did have a blue tint to it.

I also had thoughts about perhaps i didn't like the taste of smoked meat but i hope thats not the case as i have been teasing my taste buds all this time watching youtube vids of people slow cooking these ribs and beef brisket.
I will see about getting some video clips or pics this weekend when i try again maybe just a dry run.

 

[m-fine]

Here is another thought. Is it definitely wood smoke? See post 7 in this thread where someone complains about fat drippings on the reverse plate smoking.

http://www.bbq-brethren.com/forum/showthread.php?p=3809284#post3809284

You need to get the plate close to 400 to do that, but that could be an issue with your design and how you are running it.

 

[THoey1963]

Very interesting thread. A bit contentious at times, but interesting. Remember, we are here to help the OP. Any discussions that side track from that (i.e. is Feldon crap or not) should probably be in a different thread.

I agree the fire grate seems to need to be lifted up. Maybe just raise it up on some cans to see if that helps (a quick test, not an extended burn). More pictures of the inside would help too.

 

[m-fine]

Very interesting thread. A bit contentious at times, but interesting. Remember, we are here to help the OP. Any discussions that side track from that (i.e. is Feldon crap or not) should probably be in a different thread.

I agree the fire grate seems to need to be lifted up. Maybe just raise it up on some cans to see if that helps (a quick test, not an extended burn). More pictures of the inside would help too.

The issue with Feldon is not when people use it to design before they build. The problem and reason I brought it up here is that when someone has a problem with a home built, there is often a knee jerk "does it follow Feldon? If not, that is what is wrong" response.

I hate for a guy to go chopping his chimney or get out the saws and welders before we know what is really the problem.