New build tuning questions

Discussion in 'Reverse Flow' started by cuthbert, Apr 20, 2015.

  1. cuthbert

    cuthbert Newbie

    Firstly I'd like to say that everything I've done over the previous two months has been mainly based on the experiences of the contributors here, so I'd like to start out by saying thank you.

    Now for the long rambling post, but for those who are prone to TL:DR, how do you refuel your smoker at lower cooking temperatures, and how do you choke it back to lower the temp without billows of white smoke?

    I bought a cheap offset a couple of year back and have done really well with it. I decided about 8 months ago to build my own RF and spent the next 6 months looking for a suitable barrel and coming up with cheap designs. Now unlike most of the builds here, everything I have used with the exception of the wheels and the handle/fittings has come from the work junk yard/recycling so the metal is thinner than some of your more serious builds but far thicker than the cheap offset I had. I eventually found the barrel (my avatar) and started building it two months ago (I've put a picture below), the dimensions are in line with Feldon's calculator and all in all I'm happy with it. I haven't done any serious welding since my teens (along time ago) and everything seems to have gone pretty well, though already I have ideas on how to improve it ......

    Yesterday I lit it for the first time and generally I'm over the moon with it. We lit it with the firebox open and once the wood had caught we closed it in, the chimney started to draw immediately no problems at all. The cook box does need seals but it didn't leak too much. Firstly we went for high temperature grilling run and ran for 2 hours with the cook box at eventually nearly 500F, perfect clear light blue smoke (I use mainly acacia to smoke with and rarely some fruit wood, cherry etc.) We even threw a burger in to check and it was goooood.

    We then decided to try a couple of hours at a smoking temperature (my thin offset I used to run no problems for 8 hours at around 170/180 on a charcoal, thin wood splits mix) When it came to refuel we opened the cook box to let it cool down, opened the fire box put new load of wood in and after 30 mins or so once it was well and truly lit we closed it back in. Now I had no problems keeping the temperature down, but the smoke was foul, though as soon as I opened the air inlet it gave a much better smoke but of course temperature went up.

    I never had any problems with the cheap offset as I think I was mixing charcoal and wood, but this was started with charcoal and for the rest of the afternoon was all wood. The wood is good wood, been stored for over two years, didn't have any bark and I'm clueless how to get light smoke at lower temperatures. Reduce the amount of wood?

    Anyway here is the build, only needs two shelves for the outside to be finished and then sprayed. The top of the firebox is going to be replaced with a sliding half inch stainless steel plate that will act as a plancha/griddle. Any thoughts, ideas or improvements would be gladly appreciated right now. 


  2. blacktopbutcher

    blacktopbutcher Fire Starter

    Sorry I hve no advice to give but I'm interested in hearing from more "seasoned" pro's on this subject.
  3. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

  4. cuthbert

    cuthbert Newbie

     Hi Dave,
    Thanks for that, I've attached my figures for your thoughts, sorry about all the decimal places, it's all in metric (sorry)

    Comparing it to Feldon the only difference for me seems to be the firebox to cook box where as I was 100% I'm down at 62% on this calculator. Chimney is a fraction under and firebox inlet (yup 1) seem to me to be too big, but that's what I wanted to get it started.

    Gonna be hard to change where the chimney comes out now, I wanted to get it just under the cooking grill to avoid a dead zone and thought lower in the cook box was better?

    Last edited: Apr 20, 2015
  5. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Your 62% number is exactly what I found... We multiply Feldon's FB/CC opening by 1.5... that eliminates the friction loss in the smoker and allows for very good heat/air/smoke flow through it... Also, adding an upper air inlet in the FB door, directly across from the FB/CC opening, allows one to move the heat in the FB to the CC without adding air to the fire... a good adjuster for CC temp control and reducing fuel usage...
    Generally we recommend the exhaust, in the CC, be installed between the lower cooking grate and top of the CC...

  6. cuthbert

    cuthbert Newbie

    I like the idea of the upper inlet and as it so small shouldn't be difficult to add, in your opinion would that help with the smouldering dirty burn when keeping the temperature down?
    Not much I can do about the chimney, the FB to CC opening I can most probably go in there with the disk cutter but not sure I'll make the 100% but should be able to enlarge it, though I didn't seem to have any problems with the draw even when it was cold.
  7. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    With the upper air inlet, you can cool the CC and maybe open the lower air inlet a bit... It is a trial and error thing... Opening it will also act as a secondary burn for the volatiles... they are already hot and adding oxygen should burn them...
  8. cuthbert

    cuthbert Newbie

    Many thanks will give it a whirl and let you know how I get on.
  9. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

  10.  I'm with Dave    I would definitely add an upper vent in the door, I did and made a world of difference.  I looks like to me also the stack is too low and undersized

  11. smokejumper

    smokejumper Smoking Fanatic

    Welcome Cuthbert,

    Good looking smoker.

    Seems your refueling procedure might contributing to your trouble.

    Are you maintaining a small hot fire? Putting in too much fuel and choking it down to keep the temps low will lead to smoldering and bad smoke.

    Yes, reduce the amount of wood!

    You might try using a much smaller fuel load so you can let the fire burn more freely.

    Start by building a good base of coals. Lighting a chimney of charcoal at the start is a good way to do this, then add a log or two on top of this coal base.

    There should be no need to open the cook chamber to cool it down at all.

    You should only need to add one small log every 30 to 60 minutes or so with that size cooker, and it should only take about 30 seconds or less for the log to catch fire.

    As soon as the new log has caught fire, you can close up the firebox.

    The whole process of adding fuel should take less than a minute.

    Pre-heating your splits will help them catch fire quickly when you add them to the fire.
    cuthbert likes this.
  12. cuthbert

    cuthbert Newbie

    Thanks for that, The only reason I cooled it down was from having done a high temperature run. You are almost certainly right about the wood, I did load it up quite a bit. I'll do another run next weekend with the new air vent and less wood.

    I can't do anything about the chimney size, though it is the right size according to both calculators (problem with salvaging what I can from work's junk yard as well) just have to hope I get it to run at lower temp.
  13. smokejumper

    smokejumper Smoking Fanatic

    The test run you did to 500F tells me your exhaust stack is OK and draws just fine. I wouldn't change it.
  14. cuthbert

    cuthbert Newbie

    I was quite surprised how quickly it did draw, with my cheap tinny offset I always has to put the firebox in the direction of the wind to get a good draw. If you look at the picture above you'll see the size I split my logs down to, just over a foot long and thick wrist width. Being the first time I've used only wood I put about 4 of those in the basket, but if I only use one every 30 mins or so, and with the top vent I'm going to use hardly any wood at all (good news at last)

    Here's a couple of pics over the last month or so, with the exception of the chimney I think the only thing I would change if I could would be the thickness of the steel, but most vessels don't come much thicker here (took me 6 months to find this one), and getting my hands on the big propane cylinders you guys seem to find so easily just don't exist over here. The top half of the chimney comes off so I could fit the whole thing under the cover.

    Next the fire door needs reinforcing, add another shelf inside the CC, one shelf in front, one on the rounded side. The top of the firebox has to have a hole cut into it to allow for a thick stainless steel plate to make a griddle/plancha, seal the lid, spray and then just about done ...... I hope. Any other tips or ideas appreciated.

    Last edited: Apr 22, 2015
  15. cuthbert

    cuthbert Newbie

    So I drilled 2 inch hole drilled in the top of the firebox door and test run 2 can be considered a success. Thanks for all your help. 4 hours in, 2 logs and a steady 200 degrees, taken it up to 230 and down to about 170 with no white smoke apart from when it started. Still a lot of blue smoke after the refuelling, but a lot of the time the chimney ran pretty much clear.
  16. lendecatural

    lendecatural Smoking Fanatic

    That would be perfect!!!

    Great Job.
  17. smokejumper

    smokejumper Smoking Fanatic

    Nicely done!
  18. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Thumbs Up
  19. cuthbert

    cuthbert Newbie

    7 hours in and no problems with temperature control rock steady at 200, only put 5 lumps of wood on.

    Another question when you guys do long smokes using just wood, do you wrap your meat after a few hours to avoid over smoking?
    The reason I ask is when I refuel I get a lot of smoke, not smouldering white smoke, but still pretty sure after smoking a pork shoulder like I used to on a mix of charcoal and wood that it would be over smoked. I followed the calculator for the top hole side, but was thinking of making it larger to allow more cooling air in which mean I could open the bottom inlet up a bit more to get an even cleaner burn? Yay or am I barking up the wrong tree?

  20. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Use the smoker for 6 months before you decide anything....

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