UK build.....all done...I think...

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uk builder

Fire Starter
Original poster
Dec 23, 2013
Hi all from England,

I am now about to undertake a reverse flow smoker, American style.

Hopefully I've attached pictures of my propne tank.

Link to BBQ Pit Calculator

I'm planning on filling the tank with water and cutting the 1/4 opening with a petrol disc cutter.
I have a milatry axle to mount it on.

I'll try and update my progress, What do you think so far?


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Welcome to SMF!! Drop by the "roll call" section and introduce yourself. That way you can get a proper SMF welcome. You'll find that this is a great place to find expert information. Don't be afraid to ask questions, post progress. Do put up lots of pictures that is one sure way to get some help.

Please read the many threads here and learn from our mistakes and triumphs. Get a plan down on paper before you make your first cuts.

Most of all have fun, enjoy.

My 1st question:-

The calculator gives me a chimney length of 56". Is this measurement from the top of my cooking chamber? or is the measurement from where the smoke enters the cooking chamber, and chamber is included as part of the exhaust for measurement?
Basically do I need a bit of pipe 56" long or approx 32" for an exhaust?


Well, let's see:
You have a tank. Check
An axel to use on a trailer. Check
Using a pit caluclator. Check (be sure to post up your numbers so that we know what you're working with and hopefully spot trouble areas before you encounter them during the build.
You're a member of the Greatest Smoking site on the web with access to some of the greatest fabriactor's that you can bounce questions and ideas off of. Check

Looking forward to a British Smoker Build!
Hello Michael.  Have you built a smoker before?  Have you cut a propane tank before?  I don't want to offer advice that you may already know.  Some folks get offended.  RG has some good points. Put it down on paper before you make a cut, AND do some reading.  Most folks on the site also post where they went wrong and changes they might make if they were to do it again.  Good luck.

I've built a smoker out of oil drums before, this is my first out of a large propane tank.
I have cut up smaller tanks before, but this is the largest by far.
I've had the tank vented for a few weeks. I've washed it out once already. I'm going to add 20 litres of liquid soap (made from waste gylcerin from my biodiesel production) to it tonight and wash it out again.

I'm going to fill it to the brim with water and cut it when its still full.

I've done plenty of reading, I'm going to offer the axle up to it, and make the firebox out of cardboard to see how it looks before cutting up the steel.


Hello Michael.  Remove all the fittings in the top before starting the cut.  You will be fine when making that cut with it full of water but a LITTLE extra safety isn't a bad thing.  The way I have always started is to make the top cut and then tack on the hinges ( good solid tacks ),  before I finish cutting the lid.  The lid will remain completely aligned when done that way.  If need be you can grind off the hinges 1 at a time to make a change and not misalign the lid.  Before finishing the door cut, tack a piece of scrap on the door so that it overhangs your bottom cut.  That way the door will not fall into the tank when the cut is complete.  Helps keep things aligned.  Good idea about the cardboard mock up for the firebox.  Good luck.  We have a U.K. members group if interested.  Keep Smokin!

I was going to notch those top boss's out first, cut the door and then fill them in at a later date.

I did think about turning it over, but I have a large drain one in the bottom, and legs to cut off if I wanted to turn it over.

Is that the preferred method?

My thinking was 3 bosses at the top to cut out, or 1 boss and 4 legs at the bottom to cut off.

I was planning to sit it on its original legs and use the drain boss for draining fats.

I knew some to the "old" guard would visit your thread (pun intended) .  Looks like your door opening is 90 degrees of the tank circumference.  You may want to consider

making the opening somewhat less than 90 degrees.  Shorter opening at the top will keep rain water out of the cook chamber.  Just an inch or two (3-6cm).  Same goes for the opening bottom, this will keep grease and sludge from running down the front.  Smaller door opening will help with temperature recovery and not impede your access. 

Flip the tank, hide those boss patches, but I'm not sure of what the legs and bottom entail though.  IMHO

Hello Michael.  I agree with your thinking.  Leave the legs at the bottom.  What I meant was to remove the valves, plugs and such before you start cutting.  You will be fine with the tank full of water.  I don't want to scare you off.  YOUR PLAN IS SOUND AND YOU WILL BE FINE.  For an explosion to happen you need to have compression.  The gas must ignite faster than it can escape from it's container.  Removing the valves and such will allow for an escape path should any little gas ignite.  Without compression you will just get a poof.  Maybe some flames, but just a poof.  Whenever I offer advice with such things I try to be SUPER SAFETY!  Probably not needed but I just have too.  You will be fine.  Good luck.  Keep Smokin!

Well, is the one big one on the bottom anywhere near where you woud want your exhaust to be?

If so, cutting off the legs and moving them is way, way easier than patching the weld boss holes in a way that they look good. I f you can put them toward the bottom, all you have to do is install a plug and no one will see them.

Also, I agree with radioGuy about making the door a bit smaller.

I usually mount the firebox and try to get tank situated on stand or trailer before cutting the cooking chamber door.

Anyway, we are here to help!
Hello Michael.  Ya got lucky.  You attracted the attention of a few good smoker builders.  Those guys know their stuff.  You may still get 10 answers to the same question but be sure that their advice will work; even if some are conflicting.  Different ways to skin the same cat.  I just realised we never actually answered your first question.  I have not used the calculator but I have read through it.  I hope someone will correct me if I'm wrong but the stack is based on volume and is measured from the top of the tank, the way I read it.  So yes to the 56" pipe.  The length can be shortened by using a larger diameter pipe.  I could be wrong, have been before but hopefully someone will educate us both.  Good luck.


Just had an idea for all to comment on:  following on from RG's suggestion of making the door smaller, could you leave the bosses on top and then incorporate them in to a good looking door stop?  Make it look like you planned it that way.  Hard to tell from the angle of the pictures, but are they equally spaced and equally spaced from end to end?  Could you add a dummy if needed to make it look symmetrical?  Am I sad or what?  I need a LIFE!!!

Hi Danny,

Thanks for your input, and everyone else's.

The smaller door suggestions is a very good idea. I wont then have to worry about those bosses straight away and could maybe re use them like you say

The door will be lighter so less counter weights etc. Less heat loss, better recovery time, its a win win idea!

Its a very good job I registered on the forum before I made that cut!

I'll offer a couple of bits of pipe up for the chimney and see what height/diameter combination looks the best.


I hope to clarify the calculator as there are many questions on that subject. I see you have the metric to US conversion down.
I don't know of a metric version...I do find metric a lot easier...we have been going to the metric system ever since I was in grade
school...long time ago.

The calc is just a general guideline for various openings, volumes. It uses the firebox as the "reference" , but the consensus

here is to reference all calculations to the cook chamber size [since it it usually fixed tank or vessel].  That being said, put your numbers into the calc to put the FB (firebox) @ 100% or close to.  I see you are at 103% that is good enough.  All the openings, volumes with FB @ 100% would be your build to dimensions (or a bit larger...this is where the interpretations / opinions enter the discussion). 

FB size, most of what I have read is that the FB can be larger and no affect the operation.  This size can be anywhere from 100% to 130% depending upon your preference.  Definitely allow some room for ash deposit and clean out.

Smoke Stack - this is length is above the CC (cook chamber) top.   I intend to make mine a bit longer and shorten if necessary.  

After you have all your numbers plugged in, draw it up to determine the reverse flow (RF) placement height and size of CC opening. 

Here is a thread where Dave O answered a lot of questions for me.

There are numerous mathematical calculators on the web to figure out the area or volume of odd shaped objects.  Just apply a bit of logic or post a question here. 

Most important think straight line air and heat flow, reduce friction.  Place your air intakes in-line with the flow.  After all air is a fluid and heated air with smoke cooks some great food. 

Merry Christmas and Best Holiday Wishes from the USA

What size pipe are you using for you stack ?  As per Dave  the best way to insure your openings and length's are correct, is when using the pit calculator , play with your FB dimensions till you get 100%, then use the chart to size your stack and openings, after you have those dimensions you can oversize your fire box. Apparently if you put in dimensions for an oversize FB it effects all the opening and length sizes.

I was going to make the stack using either 6" or 8" pipe.

I've made the door smaller,

I picked up the axle today. It takes Land Rover wheels which are 16" standard.
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Welcome to the forum my friend….. Take it from me, ask as many questions that you can even if you thinks you may get some smart-a$$ answers in return. I have not seen anyone be disrespectful, usually if all in good fun…. What I found on this site is the members all realize some of use have never done anything like this before and quite possibly have been in that same first build situation themselves. These guys use certain words for things and there is a place on the forum that list what they are talking about. Im doing my first build and have kept from making many mistakes by reading a lot of post, liking at photos and of course asking questions. Oh…. Photos, we all like photos so post plenty of them. Good luck on your build, I will be checking it out.

Hello Jerome.  If I can help in any way feel free to shoot me a PM.  Will be the first to give you a smart a$$ answer.  
  Serious now, will be glad to help if I can.

Hello Michael.  Movin on now.  Think that smaller door is way to go.  Glad folks suggested that.  I still hope you can use those fittings as a door stop but looks like you may have to put in a fake to balance it out ( just for looks sake ).  Are you sure you can't get 15" wheels for that?  I am asking as I am no expert.  Just thinking about buying the tires.  The bigger the more expensive.  Good clean looking axle.  May I ask what it came off?  I have a reason for asking.  Are you planning to tow this smoker quite a bit and at maybe long distances? Lookin Good.  Head down, A£££ up and keep with it.  Good luck.

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