Fire management help

[SmokinBBQUK]

Hi guys,

Sorry, new member here and I stumbled across these forums whilst Googling offset fire management.

I've had a 94 gallon offset smoker for about 8 months now and am really struggling with maintaining a good coal bed and generally a good, clean fire.

I run the smoker on 100% oak wood air dried to a minimum of 20% moisture (I have a moisture meter so this is something that I check regularly) with a split size of around 8 inches by 2 inches. For the first few months of ownership I was running it at far too high a temperatures (350-400f). It transpired that the Tel-Tru gauge was inaccurate due to the prong being too short! Once I discovered this, and learned to ignore it and just use my Fireboard ambient temperature probe in the middle of the smoker, I really struggle to maintain a good temperature of around 250-275f whilst also maintaining a good coal bed.

The longer the cook goes on for the worse this becomes as the unburned wood turns into small lumps of charcoal and starts to restrict airflow, I guess. The attached picture shows what I'm left with in the firebox after an 8 hour cook. This doesn't seem right to me.

I'm now using a grate in the bottom of the firebox, which certainly helps, initially at least, but only if I bash the coals through the grate. If I place logs directly onto the coals it all just tends to go out.

The attached PDF shows the specs of the smoker that I'm running.

I've raised these issues with the builder of the smoker and one of his suggestions was to extend the stack but this would mean me having to post it to him and be without a useable smoker for the duration. As I run this as a business this isn't something that I can do. Plus, I don't feel that it is the correct solution.

I'm getting to a point where I just want to replace the smoker however I just simply can't afford to given the costs of these things over in the UK.

Any suggestions you guys have would be greatly appreciated.

Cheers,
Ben.

 

[smokerjim]

How do you adjust your air flow?, to me your not getting enough air under your wood. Maybe try lifting your grate higher.

 

[SmokinBBQUK]

How do you adjust your air flow?, to me your not getting enough air under your wood. Maybe try lifting your grate higher.

Just with the firebox door.... There is no damper on the stack.

The grate I'm using isn't standard as the builder of the smoker expects it to be ran with the fire just on the bottom of the firebox but if I do that it all just goes out :-(

 

[JLeonard]

I dont have a offset....But just looking at basic fire management I'm with smokerjim . You may need to raise your firebox grate a little bit to allow air to get under the fire. It seems to me that running it as the builder suggested your coals are setting in the burned out ash and smothering them out.
Like I said, I'm no expert but thats my 2 pence.
Jim

 

[jbruce]

Experiment. I have bricks under my grate to elevate it. Test the difference elevating the grate to different heights makes. change the direction [crossways or longways] the bricks [or whatever you use] to increase airflow. Change the location of the grate in the firebox [more toward the cooking chamber or closer to the door]. The whole idea is to make sure there is a constant flow of oxygen to the fire. heat. fuel. oxygen.

If you want to run it without a grate, you have to be more methodical about stacking to create an oxygen rich environment. If the wood collapses into a pile, less oxygen is available which reduces combustion.

 

[Smokin Okie]

There's no problem with the fire in the bottom of the firebox. The flame will get plenty of oxygen without being suspended by a grate. I've used a grate and I've burned fires in the bottom of the firebox and I can't tell a lot of difference.

That's about typical amount of ash in that pic. To initially get a split in flame, I'll prop it up on the side of the firebox or lean it on another split. But once its in flame, it should burn on top of the coal bed. Most of the time I'll have two splits in the fire, one pretty much burnt out and the other just getting started.

And really, I use the coal bed to control how a split burns. If I push a split down into the coal bed, it'll produce lower heat and a bit more smoke. If air can under the split, it'll burn hotter with less visible smoke. If my smoker is running too hot, just push the split down into the coal bed.

In order to keep my coal bed strong, I add softball size chunks of lump occasionally during the cook. I start my fire with a chimney of lump. I don't know what brands of lump you get in the UK, but most here in the States will have a mix of large and small chunks.

As far as maintaining a 25* range of temps, that's not easy to do. I can do that most of the time but a 50* range is more realistic. Stuff is gonna happen during a cook. Maybe a split won't want to catch, or another split just doesn't want to burn like the rest, or I'm burning splits with irregular shapes and sizes, or I get distracted, or I might need to go eat lunch. No doubt, trying to keep temp swings to a minimum is a good thing, but I don't worry about a 50* range.

Looking at your smoker, from the outside, I don't see a problem. That stack is plenty high. Your air flow should be good. It appears to be modeled after a Franklin smoker. It has the shelf on the firebox end of the cook chamber. The firebox looks to have adequate length. So I'm guessing there's no baffle in the exchange between firebox and cook chamber ?

Also, its my experience, that managing a fire with a digital temp probe is more difficult than using a TelTru analog gauge. The digital will react much faster to changes in temp, which causes me to react and most of the time that's too fast and I over react ......... so it leads to larger temp swings or even the fire getting too hot because I've added too much fuel.

And there will almost always be a diff between temp measured by digital vrs analog. My digital temp using a Thermoworks Signal, runs about 20* hotter than my TelTru. I can't explain that, but I only put the digital probe in the cooker because it allows me to monitor the temp without sitting in front of the Teltru analog. I would rather use the analog.

 

[Dustin Dorsey]

That smoker looks like it's trying to copy the Franklin or Mill Scale smoker. I would think the stack is plenty long enough. I run my fire sitting on the bottom of the firebox. I generally have two sticks running parallel and one or two on top. The bottom logs might tend to smoulder a bit more but the top ones catch easily. If I'm really in a groove the top logs become the bottom logs once they've burned up a little. Try to carve out a groove in the ash for oxygen to get in there. I'd experiment with cutting your splits down a bit more. They should be 10 to 12 inches long and maybe the circumference of a beer can. I mostly go by the Tel tru gauge. It's got a 4 inch stem I believe which gives me a pretty accurate reading. I rarely struggle with the coal bed. If it's good enough to ignite new sticks, it's good enough for me. Oak usually makes great coals. If the wood is too dry it turns to ash too easily.

 

[Smokin Okie]

That smoker looks like it's trying to copy the Franklin or Mill Scale smoker. I would think the stack is plenty long enough. I run my fire sitting on the bottom of the firebox. I generally have two sticks running parallel and one or two on top. The bottom logs might tend to smoulder a bit more but the top ones catch easily. If I'm really in a groove the top logs become the bottom logs once they've burned up a little. Try to carve out a groove in the ash for oxygen to get in there. I'd experiment with cutting your splits down a bit more. They should be 10 to 12 inches long and maybe the circumference of a beer can. I mostly go by the Tel tru gauge. It's got a 4 inch stem I believe which gives me a pretty accurate reading. I rarely struggle with the coal bed. If it's good enough to ignite new sticks, it's good enough for me. Oak usually makes great coals. If the wood is too try it turns to ash too easily.

Yes, carving out a groove under a split is helpful, especially with a split that just doesn't want to burn. I will rake out the groove, then turn the split sideways and lay it across the groove.

 

[Smokin Okie]

And one other thought, have you tested your analog gauge ? Just put it in some boiling water.

TelTru makes a gauge with a 6" stem, that's what's in my Franklin smoker, IIRC.

 

[Smokin Okie]

And another thought on your placement of your digital probe. Just me, but I would place the probe as close to the stem of the analog gauge as possible. And I would put my meats on the stack end of the grate. That would more accurately reflect the temps your meat are smoking.

With the probe in the middle of the grate, and depending upon whether your smoker has a baffle on the exchange, you could be putting the probe on a hot spot. Running a biscuit test would tell you where the temps are highest on your grate.

And I use the firebox door as a thermostat. If the smoker is running too hot, open the firebox door all the way. This will bring in cooler air and cool down the cook chamber.

 

[SmokinBBQUK]

And one other thought, have you tested your analog gauge ? Just put it in some boiling water.

TelTru makes a gauge with a 6" stem, that's what's in my Franklin smoker, IIRC.

Yep, I've tested the analog gauge and it is accurate. The smoker builder said he used to use a gauge with a 4" stem but people complained that it got in the way so he shipped mine with a 2" stem gauge.

I'll be running the smoker tomorrow so will try placing my digital thermometer next to my analog one and see how it goes.

 

[SmokinBBQUK]

Yes, carving out a groove under a split is helpful, especially with a split that just doesn't want to burn. I will rake out the groove, then turn the split sideways and lay it across the groove.

Cheers for that... I'll give that a go tomorrow as Friday is a smoking day!

 

[Heart of Dixie]

Have you run the dimensions of your unit thru an online BBQ Calculator to figure smoke stack length? It appears in the picture like the stack is jointed. If so, what happens if you take the top section off? You can try substituting, cheap 4" hot water vent pipe or a roll of roof flashing temporarily to adjust to the recommended length from the calculator if there is a major variance. I had to do that on my offset and it made a world of difference.

 

[SmokinBBQUK]

Have you run the dimensions of your unit thru an online BB Calculator to figure smoke stack length? It appears in the picture like the stack is jointed. If so, what happens if you take the top section off? You can try substituting, cheap 4" hot water vent pipe temporarily to adjust to the recommended length from the calculator if there is a major difference. I had to do that on my offset and it made a world of difference.

Yep, the stack can certainly be removed!

I'll have to have a test run with it removed and do some experimenting, like you suggest.

I did start to work out the smoke stack length using an online calculator but got confused by something and never revisited it... I'll have to take another look.

 

[Heart of Dixie]

Ben - I hope it helps. My offset had some draft issues, especially on very humid days and in Alabama that happens quite often. My smoker came with stack a 3" wide & 19" vertical rise. I now have 4" pipe with 34" rise. It works much better although on days with little wind and high humidity I have to keep the fire larger & hot.
Cheers
PS - my family is from the Cotswolds although I was born in the US.

 

[Hockeydudde]

Based on the residual ash, it looks like you are spreading your ashes over the entire firebox. That's a large coal bed and will either keep the chamber quite hot, it be trying to go out. It does look to be like your ash has quite large chunks to me. If you dig through it, it should be powder with no large chunks.
My advice would be try burning a smaller, but hotter fire. If you burn a fire against one end of the other, you can place logs in there on the other end to preheat, which also helps.
On my 94 gallon with 3/8" thick walls, I try to keep my fire and coal bed to about 8" x 8" and I build my fire on fire brick, which I have found helps keep the coal bed hot, really to light that next split.

 

[bill1]

I like a grate, if only because it extends the life of the bottom of the firebox. But what I see is the firebox air door just doesn't look to me like it makes it easy to make small changes in air flow which I think you're going to need after you get all that steel up to temp. That might be why you had better luck with 350F cooks than 250F.

Can you use a spring of some sort to pull the air door closed but then use a wedge (e.g. the kind they sell to hang door frames) to make small adjustments in its opening?

Such fine-tuning isn't easy when you're starting out and takes a time commitment both to learn and again with each cook. This is why many folks give up and get a set-and-forget cooker like a pellet machine instead. Asking questions is great, but there's no teacher like experience. Don't give up and keep us posted.

 

[SmokinBBQUK]

Based on the residual ash, it looks like you are spreading your ashes over the entire firebox. That's a large coal bed and will either keep the chamber quite hot, it be trying to go out. It does look to be like your ash has quite large chunks to me. If you dig through it, it should be powder with no large chunks.
My advice would be try burning a smaller, but hotter fire. If you burn a fire against one end of the other, you can place logs in there on the other end to preheat, which also helps.
On my 94 gallon with 3/8" thick walls, I try to keep my fire and coal bed to about 8" x 8" and I build my fire on fire brick, which I have found helps keep the coal bed hot, really to light that next split.

The residual ash is a build-up over the length of the cook, not an indication of how large my burning coal bed is, if that makes sense.

I don't have a particularly suitable grate so most of the coal bed falls through and sits on the firebox floor. This actually seems to work well though as I then just place the logs on the grate, over the coal bed and they burn well. In doing this though the unburnt charcoal in the coal bed gets pushed back, behind the active coal bed and builds up, to a point where most of the firebox is filled with it, which I know can't be right..... This also means that my active coal bed gets gradually pushed forward during the cook.

 

[SmokinBBQUK]

I like a grate, if only because it extends the life of the bottom of the firebox. But what I see is the firebox air door just doesn't look to me like it makes it easy to make small changes in air flow which I think you're going to need after you get all that steel up to temp. That might be why you had better luck with 350F cooks than 250F.

Can you use a spring of some sort to pull the air door closed but then use a wedge (e.g. the kind they sell to hang door frames) to make small adjustments in its opening?

Such fine-tuning isn't easy when you're starting out and takes a time commitment both to learn and again with each cook. This is why many folks give up and get a set-and-forget cooker like a pellet machine instead. Asking questions is great, but there's no teacher like experience. Don't give up and keep us posted.

All I can do is simply adjust how open the firebox door is as there are no dampers within the door itself. This does allow me to adjust it fairly well though, or at least that's what I think.....

 

[SmokinBBQUK]

And another thought on your placement of your digital probe. Just me, but I would place the probe as close to the stem of the analog gauge as possible. And I would put my meats on the stack end of the grate. That would more accurately reflect the temps your meat are smoking.

With the probe in the middle of the grate, and depending upon whether your smoker has a baffle on the exchange, you could be putting the probe on a hot spot. Running a biscuit test would tell you where the temps are highest on your grate.

And I use the firebox door as a thermostat. If the smoker is running too hot, open the firebox door all the way. This will bring in cooler air and cool down the cook chamber.

You were right.... I placed my digital probe right next to my analog stem and ran with it there for the entire cook. I managed to keep within a range of 210 - 250f and when I placed the probe back in the middle as a test it was reading around 50f higher.

This means I've probably been running my cooks a little low on the temp, which probably explains why I've struggled to get good fat render on the last few Boston Butt's that I've done.....