Air FLow

Discussion in 'Smoke Houses' started by archeryrob, Apr 11, 2016.

  1. I have a DSSG barrel stove door on the brick firebox and have didn't use a chimney as I read a thread here about the "crack between the boards" would be enough. Apparently I fitted my boards too tight and don't have good flow. I crack a board loose and still didn't get over 140 without cracking the stove door. With it cracked and the board loose like a chimney I was able to get up to 175 before I shut it down, but the fire was going pretty good. I assume once I got a bed of coals I would maintain heat better, but I need input on getting better air flow and heat to cook bologna and jerky.
    Last edited: Apr 11, 2016
  2. I am thinking about getting a small piece for 4" schedule 10 pipe from a friend and welding a 90° chimney with a cap. Might add a damper to it also.

    Thoughts or suggestions?
  3. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Pictures of the smokehouse.....   

    I'm thinking a whole bunch of 1" holes drilled around the "near" top of the walls...   That way, no condensate to drip on food....  even air distribution throughout the smokehouse...   etc....    I'm not a fan of exhaust pipes because they can cause linear air flow inside the smoker.....   As an example.....   my MES 30 has an exhaust hole on the back right top panel of the smoker....  That causes a high temp zone inside the smoker on the back right part of the food racks.....    Holes drilled all around the top portion of the exterior walls will "eliminate" hot spots caused by the exhaust....
  4. So I could drill small holes in the tops of the sides (under the roof) and would there be a need to damper it in any way? I can't drill the front without drilling the door and the front and back are likely to let in wind blown rain.

    I am sure I will need to "screen" the holes as the first thing out of my wife's mouth will be "bugs will get in it now."

    So I should start with 2 one inch holes on each side and see how many more I need after that? Or should I start with 4? I don't want to drill too many holes as this old barn wood isn't cheap. [​IMG] No need to damper the holes, I guess?

    Here is the smokehouse right now and that is my waterfowl hunting partner that just had to be in the picture, or beat me to where I was going. The frame, trusses and soffit blocking is all 2x4 pine. The outside exposed soffit it pressured treated pine and so it s the 4x4's and fire wood rack support I am still finishing. Siding boards are also pine, but replaned barn siding wood I got from one of our Mennonite buddies.

    Last edited: Apr 13, 2016
  5. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Front and Back....  under the eave....  You could put adjustable floor vents from a forced air furnace...

  6. My roof is not part of the smoking area. I used OSB plywood and metal roofing and didn't want the OSB glue exposed to the heat/food. I have a flat wood pine ceiling inside and that is why I would have to drill the door to put in in the front. If I used those I would have to put them in the front ot back of the sides as I have a 2x4 square in the middle of the sides.

    But, do you have to use a damper, is it useful? I could drill 1 1/4" holes and thread cut 1" nipples into the holes and weld a nut to the cut and and add plates later to cover the holes to control flow by having some open and some closed.
  7. So Yesterday I did the math and drilled some holes. I will find out later if I need to find a way to damper some of them That seems to choke the fire, but I never got it very hot on the first fire build.

    A 4" round chimney would have a 12.5" sq in. area. I was going to drill 8 holes and I was planning on using 1" holes but went with 1 3/8" holes for why I'll explain below

    1" hole = .78 sq in area

    1 3/8" hole = 1.48489 sq. in area

    4" Hole = 12.5 sq in area

    .78 x 8 = 6.24 sq in area

    1.48489 x 8 = 11.87 sq in area

    Increasing the 8 holes 3/8" almost doubled the exhaust area. I'll report more after I have time to use it. I just got the firewood rack built yesterday and have too many other projects and "to do" crap to get done.
  8. I split some cherry logs I had for firewood and ran another test burn. I think some of my previous problems was a lack of patience. I had to leave the door cracked until I got the firebox good and hot. I am going to replace the clip that holds the door latch with one that is stepped. Then the latch can sit on a step and stay secured while leaving the door cracked. Then I can close it when its good and hot.

    Once the roof and all the brick was hot it flowed much better. I was able to keep 180 to 190 if I wanted too and could stifle it to bring it down to 140 - 160 for making jerky. Part of the air flow was not just the chimney holes but also the fire box being good and hot.

    Now I just have to make jerky trays and I am ready now for Bologna and snack sticks.

    Here is the 4 holes on the short rood side. I have the same 4 under the long rood side. Since my roof is open I put rat screen to keep the birds from building a nest up there.

    Last edited: Apr 20, 2016
  9. txdvr

    txdvr Fire Starter

    Nice looking build!
    Post pics of the meats!
  10. I was posting in the curing section lately. I just did my first meats today after a 10 day cure with 2 goose breasts and a deer shoulder de-boned.

    Short story, I am going to slice it and have pics tomorrow and the plastic anchor melted out and the door fell off my fire box and 7/8th of the way through. Its always exciting around here with my new projects. [​IMG]  

    I still have to work on air flow. I have enough to make fires and cook things but Dave just educated me on needed a chimney bypass so  can cold smoke. Once that brick gets hot, its frickin' hot!! More work and engineering to do.
    Last edited: Jun 16, 2016
  11. OK, now I have too much flow. Dave told me on the Curing forum that old time smokehouse had a way to release heat from the fire box, or vent some of the smoke stack.

    Anyone done this or know of a setup that did it they could point me too? My pipe is set in the masonry in both ends I really don't wish to be knocking the crap out of all that again.
  12. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Rob, leave the FB door open and see what the temps are...

    You can use a hole saw for the duct..  right where it comes out of the FB...   put a 6' vertical piece of pipe on it with an inline damper...  make the hole a bit smaller than the vertical pipe... cut a "TEE" in half and slide it over the smoke pipe and screw it down......

    Don't forget you can add air inlets at the lower portion of the smokehouse...   to see the results, start a fire and open the smokehouse door... that should almost stop the draft... 

    Open the FB door and let the heat out at the door... 

    Experiment with all of the options before you make permanent changes...

    Last edited: Jun 18, 2016
  13. txdvr

    txdvr Fire Starter

    Good afternoon Dave, I have seen your comment of the "T" and I am trying to figure out exactly how you are meaning for this to be built.I plan to build my smoke house using a flue liner from the FB to the smoke house, so is there a drawing or other detail that you can provide to show me what you mean by adding the "T"?
    I know you have mentioned in previous posts that a clay liner would help with the heat better than a metal pipe, so I am planning to go that route.
    The problem is the flue liners I have found are only up to about 24" long and the one I am considering is 8"x13"x24" , so that may be too close to the smoke house. Not sure if I can add more than one together or not... Still researching that.
  14. I could easily do that Dave and thanks for the idea. I could drill with a 2 1/2" hole saw and I am thinking about using 4" pipe and sliding it over the hole. Although a 6" hole and pipe might make future damper maintenance a lot easier. Then I would need a 6" damper and 4" damper. My biggest concern is the exhaust pipe is right neat the smokehouse roof and fire wood. I would like to block the rain from it, but might need to use a 90° and make some kind f rain hood for the 90 opening.

    TXDVR, I was going to use the flue pipe too, but them read about it being fairly brittle and it needs to be covered with brick for protection. So I did not use it for that. I assume you could hand make a damper for a flue pipe but imaging you'd have to drill it with a non-hammer drill to make a hole and extend that through the brick. As fragile as that flue pipe is, having a damper sounds like a problem to me. you might be able to make a slot with brick that is not mortared to the SH base and the flue not motared there also. Then a flat metal plate with a lip could be slide in there as a damper.

    To make an exhaust, I am not sure they even make a Tee for that. Its made for each fired appliance to have it own chimney and not to share them. You'd have to use a chisel to make your own Tee. Plus then you wanted to run the SH hot, you'd need a damper for the exhaust or a cap for it.
    Last edited: Jun 20, 2016
  15. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    The smokehouse needs upper and lower air inlets so it will have good airflow...   The Firebox needs upper and lower air inlets to control the temp of the fire...   The upper air inlet on the FB will cool the exhaust temperature a bit...  The "TEE" stack is adjustable to allow for dumping of heat and smoke...  The FB upper air inlet helps to control that temperature and amount of smoke...   Some of the really old smokehouses I've seen, they prop the Firebox door open and use it to adjust the smoke and heat....    Once the smokehouse gets warm, it acts as a chimney and sucks smoke and heat from the FB...  Regardless of all that, the smokehouse needs it's own separate air in / air out vents... When smoking meats, you cannot have too much air flow...   When I worked at Hempler's as an outside contractor welding up their SS smokehouses, the air flow inside the smokehouses was similar to a hurricane...  That way they insured uniform distribution of heat and smoke and the racks with 500-1000 #'s of meat on them (there were 6 in each smokehouse) would all get uniformly finished AT THE SAME TIME....

  16. txdvr

    txdvr Fire Starter

    Thank you gentlemen!!
    Makes sense now!
    Now I can figure that into the plan.
    So Dave, do you think the flue liner is the way to go, or pipe?
    I want to cover it up with the same material as the smoke house base anyway for "curb appeal"...
    Thanks again!
  17. I am going to do the bypass, but not so sure on the lower in take holes. They will be where rain can get to them. maybe later on after I use it a bunch and I need improvement or not if it works out.

    I was figuring on two dampers, one of the bypass stack and one to the smoke house for better control. One open and one closed or both varying degrees as I want it.

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