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outlawbbq2013
05-08-2017, 09:44 PM
I have a smoker mounted on the back of my fire truck. The smoker is 13 ft long 40 inches high and 40 inches wide. The fire box is at the one end. I can't get the temps up to where I need to and the heat from the fire box is almost unbearable. It has the tuning plates and two stacks that are 6inch diameter on it. Want to know do I need bigger stacks? More air in? Fans to push the heat and smoke down to the other end? Any help would be great.

SmittyJonz
05-08-2017, 09:46 PM
:shock:

Stlsportster
05-08-2017, 09:57 PM
I would think we need more information. The size of the firebox, the dimensions of the opening between the firebox and smoke chamber, etc. How tight are the fittings at the welds and doors? Is it pretty airtight?

Take a look at this thread of a 600 gallon smoker build. I would guess it's pretty close to the size of yours.
http://www.bbq-brethren.com/forum/showthread.php?t=211078

bwram1
05-08-2017, 10:08 PM
Well...if, in the first pic, that is the firebox dropped down between the cooker and cab of the truck...looks extremely small for that cooker size. But...is that it running the width of the cab in the second pic? If so, I dunno. As stated above, firebox LWH would help.

outlawbbq2013
05-08-2017, 10:22 PM
The fire box is at the one end and it is 24x24x24. The opening to the pit from the fire box to the cooker is only 20x8. There is a little leakage around the doors but not very much. I was thinking that with the fire box being way to hot and I don't see a lot of smoke coming out of my stacks that the stacks need to be bigger to draw more air out through the smoker.

bwram1
05-08-2017, 10:24 PM
The fire box is at the one end and it is 24x24x24. The opening to the pit from the fire box to the cooker is only 20x8. There is a little leakage around the doors but not very much. I was thinking that with the fire box being way to hot and I don't see a lot of smoke coming out of my stacks that the stacks need to be bigger to draw more air out through the smoker.

Firebox is way way too small...should be an estimated 1/3 of the cook chamber...I think. Others on here are more qualified to give you specifics, but I can safely say it is far too small.

Pstores
05-08-2017, 10:28 PM
This is what you should use to size everything
http://www.feldoncentral.com/bbqcalculator.html

outlawbbq2013
05-08-2017, 10:31 PM
I don't think there is going to be an option for making it a third of size of the cooking space. Will have to take a look and see.

Pstores
05-08-2017, 10:32 PM
From your deminsions...... Your firebox is 15% of the size it should be. I would make if 120% and go over sized....

jmellor
05-08-2017, 10:33 PM
"I have a smoker mounted on the back of my fire truck"

One of the best opening lines I have seen on a thread here ever. Well done! Back to the brethren that can actually help....

Joe Black
05-08-2017, 10:33 PM
According to my calculations, that monster is 1081 gallons. With that, the FB should be 3'x4'x4' for 48 c.f. or 360.4 gallons

bwram1
05-08-2017, 10:34 PM
This is what you should use to size everything
http://www.feldoncentral.com/bbqcalculator.html

Yeah...I entered the 40"H, 40"W and 156"L...then entered 24" cubed firebox...tells me that the firebox is only 16.6% of the size it needs to be.

44" cubed would get you to 102.4%...so that is about where you need to be. Then you would likely need to increase the opening to chamber and have multiple bigger intakes. Stacks can't draw more air than intakes are allowing in...

Jason TQ
05-08-2017, 10:38 PM
Just your Classic "insanely massive smoker mounted on the back of a guys personal firetruck having trouble with temps" challenge. We get that a lot around here.

You should see the smoker I have on the back of my space ship! :twitch: :twitch:

But ya. Whatever the guys are calculating for ya :becky:

Pstores
05-08-2017, 10:38 PM
Yeah...I entered the 40"H, 40"W and 156"L...then entered 24" cubed firebox...tells me that the firebox is only 16.6% of the size it needs to be.

44" cubed would get you to 102.4%...so that is about where you need to be. Then you would likely need to increase the opening to chamber and have multiple bigger intakes. Stacks can't draw more air than intakes are allowing in...

Yep.... I used 168 for some reason... Your numbers are correct....

Pstores
05-08-2017, 10:45 PM
I don't think there is going to be an option for making it a third of size of the cooking space. Will have to take a look and see.

Well, have any other ideas for the fire truck? Parades maybe. Because without a firebox 1/3 the size of cook chamber...... Your fires out..... Good luck let us know how it turns out. May just have to redesign the entire thing. Atleast it is steel and can be cut and rewelded as many times as needed. That's the bright side of this story. Sorry about the bad news,

Stlsportster
05-08-2017, 11:25 PM
Just your Classic "insanely massive smoker mounted on the back of a guys personal firetruck having trouble with temps" challenge. We get that a lot around here.

You should see the smoker I have on the back of my space ship! :twitch: :twitch:

But ya. Whatever the guys are calculating for ya :becky:

I thought you had that smoker on the back of your canoe?? :crazy:

ehs5mw
05-08-2017, 11:52 PM
:shock:

How did you get this picture of my face when I looked at these pictures!?

Jam Jam
05-08-2017, 11:52 PM
I don't have any experience with welding pits but from my perspective the only way you can make it work is to turn the pit around. Otherwise you won't be able to expand the firebox and with the way it's setup now radiant heat must be a nightmare, it looks like it would heat the entire cabin.

Jam Jam
05-08-2017, 11:55 PM
Or at least chop the firebox and put it on the other end.

McSpazatron
05-09-2017, 12:15 AM
This is super cool!!! But more picture please (the firebox and interior cookchamber).

Honestly with that much cooking space, you could try redesigning it with an internal firebox on the end of the cooker. Heck, you could start out by just cutting a door on the end and drop wood straight into the bottom of the cook chamber, then take it from there. That way you keep all the heat inside, and limit waste heat. You would need to keep grease out of the fire, but you could weld in some sort of grease dam in there. Probably way easier and more efficient that making a whole new external firebox.

Also, it would be nice to see where the cooking racks are. With that much vertical height, there are probably huge temp variances top to bottom. I might even venture to guess that the lower grates on the exhaust side would stay pretty close to ambient temp, even with a proper firebox (depending on how far down your grates go). Especially considering that your heat is making a beeline straight to the exit, which is right on top. If you need cooking temps, you might have to use the top racks. And use the bottom racks as a warmer.

bwram1
05-09-2017, 12:31 AM
Perhaps you could weld some plate in the center and create 2 separate cook chambers of 40"x40"x78"...then you could increase the existing firebox to 36" cubed and duplicate it on the rear...that would get you to about 112%. Would also give you the ability for low n slow and hot n fast cooks simultaneously.

Jason TQ
05-09-2017, 12:02 PM
I thought you had that smoker on the back of your canoe?? :crazy:

Ya, but it's not that big!

SmittyJonz
05-09-2017, 12:18 PM
You could cut off the firebox and toss it and make the first cook door area an internal Fire box. Weld in a side and top to what's already in there - (an L rotated 180* backwards). Get your intake right size and your hole from firebox to chamber right size. Still gonna have a big temp drop across a pit of that size.

Better yet is to add an internal firebox dead center with access from outside (door to feed it and large intake or door could be the intake) and put smoke stacks on both Ends. :heh:

Pstores
05-09-2017, 09:13 PM
You could cut off the firebox and toss it and make the first cook door area an internal Fire box. Weld in a side and top to what's already in there - (an L rotated 180* backwards). Get your intake right size and your hole from firebox to chamber right size. Still gonna have a big temp drop across a pit of that size.

Better yet is to add an internal firebox dead center with access from outside (door to feed it and large intake or door could be the intake) and put smoke stacks on both Ends. :heh:

Or for versitility you could add a firebox on the end. Put stacks for in the middle or make it a reverse flow. And separate into to separate smokers. Different temps. Doo what Smitty says and resize everything to the proper size for the volume. Then you may have someting......

TJR89
05-09-2017, 10:30 PM
Many good suggestions on resizing and/or reconfiguring so ithink they have you covered there. I just wanted to comment and say how awesome it would be to have a cooker big enough to be on a firetruck! Very cool project and i hope you get it worked out.

Shagdog
05-10-2017, 08:43 AM
I need so many more details.. Why?? How? What are your plans for that beast? and more pics please! That thing is massive!

Sounds like you're going to need a lot more Firebox to make this work.. If you put the Firebox at the other end, you could either turn it into a reverse flow, or move the stacks. Oooh you could do vertical stacks like on a semi! That'd look cool. Hope you figure it out

IXL
05-10-2017, 09:02 AM
You might try opening the door closest to the stacks, to see if more outflow volume will improve things. Also, open the fire box door completely. It's possible that this would inform you as to whether or not will flow air at all.
The fire box is to small by a good bit, but if this test works it should at least be possible to increase the stack diameters and get the cooker up to your desired temperatures. As such, you would probably be adding one or two splits about every four minutes.

bucko
05-10-2017, 09:02 PM
This sounds more like geometry than bbq

IXL
05-11-2017, 10:42 AM
Better living through math......

outlawbbq2013
05-11-2017, 03:07 PM
A couple of thoughts.
1. Would adding in line duct fans to the stacks help to move the air through the smoker more?
2. Also thought about putting a wall down the middle and another fire box on the other end and have two separate cookers.

I can make the fire box bigger but not a third of the size of the cooking space. The biggest I think we could go would be 24x24x48.

Thoughts?

SmittyJonz
05-11-2017, 05:05 PM
Yup I'd go internal firebox........

Like this but on a much bigger scale........

http://www.peoriacookers.com/custom-cookers/meat-monster-mif.html


I'd have to see more of the Smoker but I would Really look at a center firebox internal with stacks on both ends.

Pstores
05-11-2017, 08:04 PM
A couple of thoughts.
1. Would adding in line duct fans to the stacks help to move the air through the smoker more?
2. Also thought about putting a wall down the middle and another fire box on the other end and have two separate cookers.

I can make the fire box bigger but not a third of the size of the cooking space. The biggest I think we could go would be 24x24x48.

Thoughts?

Two separate cooks could be handy. Or a pain..... Lol.... Did you run the numbers for the 24x24x48?

McSpazatron
05-11-2017, 08:53 PM
Im liking Smitty's central internal firebox idea. Add stacks to the other side.

I would avoid fans to induce flow. To bring the cooker up to temp, you would probably have to stoke such an intense massive fire in that tiny firebox, that it could be dangerous. Especially sitting a truck chassis with flammables around. Not to mention you would have complete combustion with such an intense fire, so no smoke flavor. And you already mentioned the heat was intense as it stands.

Pstores
05-11-2017, 09:10 PM
Im liking Smitty's central internal firebox idea. Add stacks to the other side.

I would avoid fans to induce flow. To bring the cooker up to temp, you would probably have to stoke such an intense massive fire in that tiny firebox, that it could be dangerous. Especially sitting a truck chassis with flammables around. Not to mention you would have complete combustion with such an intense fire, so no smoke flavor. And you already mentioned the heat was intense as it stands.

Would have to agree.... Fan idea bad.

Jason TQ
05-14-2017, 05:00 PM
I'm sorry..........but did we seriously not address the fire truck and how there is a big ass smoker on it??

Nuco59
05-14-2017, 07:06 PM
It is awesomeness x10.... but you still have to be able to cook on it - or it loses "something"- still cool but...

Notorious Q.U.E.
05-14-2017, 07:14 PM
Agree Jason TQ,

I mean talk about a water reservoir for the cook chamber. I think some fire engines have 500 gallons of water internally. You could get a transfer pump internally to regulate humidity in the pit. With tons of expendable cash, the sky is the limit!

outlawbbq2013
05-18-2017, 02:59 PM
Ok so an update on the smoker. We cut out a section of the fire box door to allow for more air flow. Also took the stacks off and cut a bigger rectangular hole with a stack that is four feet above the smoker. Lit a fire in it and the smoker did quite well. All the chambers were even. Had all four chambers at 300 degrees in 28 minutes. After 50 minutes all the chambers were at 375 degrees. Loading it down with meat tomorrow and if it doesnt work like it should then we are building a bigger fire box and bigger opening to the cook chamber from the fire box.

cfrazier77
05-18-2017, 04:08 PM
First, as a former firefighter this is crazy amazing. I would endorse the previous stated idea of putting in a wall in the middle to separate it into two smokers and add another firebox on the back. I would also make the one you currently have bigger.

To me why I would do this is to be able to run two different temps.

And this is an amazing smoker! If you could put a beer tap on the other side it would just blow minds!
:boom:

SmittyJonz
05-18-2017, 05:00 PM
Let's see pics of your improvements......

cats49er
05-18-2017, 08:24 PM
Have you thought about insulating the firebox,or the whole smoker even?Insulating firebox would cut down on radiant heat.

Rusty Kettle
05-18-2017, 08:38 PM
I hope that works out for you. It looks cool. A smoker mounted to a fire truck. Never would have thought I would see that. You sir have surprised me and that is hard to do. Thank you for making my night. :)

wihint
05-18-2017, 08:51 PM
Pretty freakin cool! Glad the bbq gurus could offer some help.

MisterChrister
05-18-2017, 09:14 PM
This thread kicks azz! You have good problems, my friend! Looking forward to the cook pics and more follow-up!

Jason TQ
05-18-2017, 09:50 PM
Ok so an update on the smoker. We cut out a section of the fire box door to allow for more air flow. Also took the stacks off and cut a bigger rectangular hole with a stack that is four feet above the smoker. Lit a fire in it and the smoker did quite well. All the chambers were even. Had all four chambers at 300 degrees in 28 minutes. After 50 minutes all the chambers were at 375 degrees. Loading it down with meat tomorrow and if it doesnt work like it should then we are building a bigger fire box and bigger opening to the cook chamber from the fire box.

Still not getting the picture.........

How did a big ass smoker get to be on a firetruck?? Did you acquire the package this way or buy the firetruck and be all like "this son of a b$tch needs a massive smoker pimping off one side so let me get on that"? :-D

Jason TQ
05-19-2017, 08:30 PM
Still not getting the picture.........

How did a big ass smoker get to be on a firetruck?? Did you acquire the package this way or buy the firetruck and be all like "this son of a b$tch needs a massive smoker pimping off one side so let me get on that"? :-D

Or did you have the massive ass smoker to start and were all like "Damn! This big ol Mofo smoker needs a freaking fire truck strapped to it, so let my ass hop on craigslist and take care of this situation proper!"

.........Or are we not going to find out??:-D

m-fine
05-19-2017, 10:48 PM
This is what you should use to size everything
http://www.feldoncentral.com/bbqcalculator.html

That calculator is absolute garbage. It does not use the correct inputs to design a smoker, so don't expect it to give good results for a device that is larger or smaller than whatever they used when coming up with their ratios.

Pstores
05-19-2017, 10:57 PM
That calculator is absolute garbage. It does not use the correct inputs to design a smoker, so don't expect it to give good results for a device that is larger or smaller than whatever they used when coming up with their ratios.

Well it seems most people from forum to forum would disagree with your thoughts. It is all based on ratios of input vs output vs cook chamber...... It maybe 5-10% out of ratio, but it's pretty close to what you should have.

m-fine
05-19-2017, 11:17 PM
So, by your modified results, you can see the Feldon calculator telling you to make the fire box massive is not exactly accurate.

The problem(s) you have are lots of surface are for heat loss, and a long length. The best suggestion in this thread was to insulate it. If you can reduce the heat loss out of the cooking chamber, you could easily run a smoker that size with a firebox 1/4 the size of yours with only a single 6" chimney. The volume of the cook chamber is irrelevant, what maters is the surface area and R/K values, neither of which enter in Feldon's oft quoted pile of crap.

The 2x2x2 firebox can kick out plenty of BTU's if you get the air flowing and more airflow will help keep the exhaust end from being too much colder than the firebox end. I would still both insulate as much as you can, and work on airflow. That will give you more stable consistent and manageable temps, and more moderate fuel use.

A taller chimney will produce more suction and help make up for a smaller intake and chimney area, but you don't want to go too tall on a mobile smoker. Cold air is denser than hot, so the intakes can be a bit smaller than the chimney area, and the exit from the firebox should be larger than the chimney area. Exactly how big is going to depend on the insulation and how hot you want to be able to run it, but you don't need precise calculations to get to a setup that works well.

Pstores
05-19-2017, 11:28 PM
Feldons wasn't created for insulated cook chamber..... Obviously that would help.... Depending on how well and what you insulate

m-fine
05-19-2017, 11:30 PM
Well it seems most people from forum to forum would disagree with your thoughts. It is all based on ratios of input vs output vs cook chamber...... It maybe 5-10% out of ratio, but it's pretty close to what you should have.

I have a degree in aerospace engineering. I actually studied thermodynamics, airflow, and combustion. I guarantee you whoever came up with the formulas in that calculator didn't have any background in engineering.

Think about it. Does cook chamber volume make any sense as an input? Do you think a cook chamber that is a 4'x4'x4' cube has the same BTU requirements as one that is 1'x1'x64'? If not, why would the firebox size, openings and chimney be the same? Do you think a cook chamber made with 28 gauge sheet metal has the same BTU requirements as one made out of 1/2" steel, or one that is made out of two layers of 1/4" steel with 2" of insulation in between? The difference in heat loss could be 10x or 100x depending on your choices, and yet Feldon thinks they are identical. That is crap.

My best guess is that the calculator was made by someone looking at a few designs that worked and trying to back into a formula without a clue what they were doing.

Pstores
05-19-2017, 11:37 PM
I'll have to check. But I believe the guy that came up with it is a Thermodynamics Engineer. From Smoking meat Forum. And has worked with a couple top performing BBQ Pit makers. Could be wrong.... But I'll look into it later this weekend.

m-fine
05-19-2017, 11:50 PM
If the original formula came from an engineer, a lot was stripped out in translation. Such as "only valid for X ranging from Y to Z". The calculator will end up producing a smoker that works as long as you use relatively "standard" shapes, sizes, and materials. That doesn't necessarily apply to a giant smoke built onto a fire truck. As you get bigger and more unusual, the results it spits out become absurd.