Draft flow/top vent calculations...

[indaswamp]

So, I built a smokehouse in March/April 2017. Here is my build thread for reference pics.:
https://www.smokingmeatforums.com/t...ard-outhouse-smoker-build-pics-addded.261865/

I have been using the heck out of it, but for smoking under 170* when making sausage, I am having to crack the doors (top and bottom) open to regulate the heat. My questions are pertaining on how to solve this issue.

Currently I have a general High pressure propane burner; think it is a 15000 BTU. I am looking at converting to a low pressure regulator and going with this burner from tejas smokers:

https://tejassmokers.com/Cast-Iron-Burners/24

I can pipe the venturi outside the smokehouse to pull in clean air for the flame combustion, and this will also help with draft.

My question is, I basically used this smokehouse as a guide:
http://lpoli.50webs.com/text_files/build_smokehouse.pdf

But I went 2.5' X 2.5' X 6' instead of 2' x 2' x 6'. I have roughly 36cu.ft. of space. I have (2) 2" holes for top vents, one on either side. I have (2) 2" holes about 6" off the bottom of the smokehouse, one on either side for air intake. As shown in the design plans above.

With those 2" holes, do I have enough draft through the smokehouse? Should I add 2 more 2" top vents? Will adding the more top vents help me with not needing to crack the doors?

I have been trying to smoke sausages when it is cold, below 32*, and that helps a lot being able to control the smokehouse temp., but I am still needing to crack the doors slightly when doing low and slow @ 120~130*.

Any ideas would be helpful. Thanks in advance.

Maybe just going to a low pressure regulator and burner will help fix this issue. Eventually I want to go to a PID controller with an auto valve and pilot. I get nervous about flame outs on windy days and would feel much safer with an auto system with a pilot.

 

[indaswamp]

I am also considering fabricating a 'doughnut' ring that I can use to cover the outer ring of propane jet holes which will effectively half the BTU's the burner is putting out. This way, I can run just the inner ring of jets at a higher output and this would help prevent flame out. Doing some reading on the web, I may need to fabricate an insert for the feed pipe from the venturi to the burner to reduce the dia. of the hole size to ensure good mixing of the gas and air when using the doughnut.

 

[daveomak]

Reduce the BTU output of the burner... Install a screw in every other one of the burner holes.... self drilling screws would work.. get a low pressure regulator that you can regulate the pressure... Get a needle valve to finely adjust the gas flow.... Add 2 more 2" outlets at the top of the smokehouse... Expanding gasses could almost double the needed exhaust holes... 2 for inlets and 4 for exhaust should be close to what you need...
Here is what one member did to solve his high temp problems....

 

[indaswamp]

Thank you Dave for the reply!

 

[indaswamp]

Low pressure system is the way to go....
Picked up a needle valve and the correct orifice today. Hooked everything up and did a test run-no wood. I can turn the heat down to a 1/8" small blue flame and hold the smokehouse @110*. Held it there for about an hour. Then cranked it wide open to see how high I could get it. Currently running @265*, but took about an hour to get there.

I'm using a king kooker WKAF2B 18,000 BTU 11" WC LP burner. Looks like there will be no need for me to block any jets for this burner. I hooked this one up as a test run. I have the Tejas 30,000 BTU burner with external venturi and will install it when I increase the flew size.

Now I know roughly what I need for BTU's. I'm happy.

 

[indaswamp]

@275* on the top, 260* on the bottom now.

This is with no wood and no meat in the smokehouse. If I increase the BTU's by 1/3 to 30,000 I should have enough reserve heat for when filling the smokehouse up with meat. The biggest change though was going to a low pressure 11"WC system. Much finer control over the flame.

 

[daveomak]

Low pressure system is the way to go....

I'm using a king kooker WKAF2B 18,000 BTU 11" WC LP burner. Looks like there will be no need for me to block any jets for this burner. I hooked this one up as a test run. I have the Tejas 30,000 BTU burner with external venturi and will install it when I increase the flew size.

To keep from having a "flame out".. You might consider blocking 1/2 the burner jets... unless you have a flame sensor to turn off the propane flow....

 

[indaswamp]

Holding steady @ 282* on top, 271* on bottom.

Dave, That is the plan when I install the Tejas burner with external venturi.

This was a test run for figuring out the regulator and BTU requirements. I'll post pics. when I start installing the system. I'm also installing a safety shut off valve.

 

[indaswamp]

Oh, and Dave, I think the blow outs were more prevalent with the high pressure regulator than the low pressure one. It was breezy and gusty this afternoon- not one blow out even with a low flame.

 

[indaswamp]

I preparation for smoking 150lbs. of venison sausage in the next few days, I decided to try and cut the BTU's in half on the burner. I wanted something temporary as a test, this is what I came up with...

4D nails cut down and inserted in the burner holes...

Took about 5 minutes using plyers to snip them. Inserted in the outer ring of jets..

Been down with the flu for the last 3 weeks...finally feeling better. When I catch up and get some time I'm going to install my Tejas burner with external venturi. This ought to suffice until then.

 

[daveomak]

GREAT JOB !!! Thinking outside the box again HUH !!!!

 

[indaswamp]

GREAT JOB !!! Thinking outside the box again HUH !!!!

<thumbs up>
Yep!

 

[indaswamp]

This is working real good Dave. Smoking 100# of sausage today, wind is gusting to 20mph and the flame is still lit-no blow-outs. I can fine tune the temp. +/- 3*.....

Awesome!!!!!

 

[daveomak]

How cool is that.... REAL COOL !!! Congrats on the improvement to your temperature control....

 

[indaswamp]

I'm Happy, Happy, Happy!:D

 

[indaswamp]

Smoke is going sideways today....LOL! Another stiff wind day, but the burner is chuggin along great!

 

[daveomak]

Are you just "TESTING" the burner or are you smoking something...

 

[indaswamp]

Dave, I'm smoking all the sausage we made Tues/weds.
https://www.smokingmeatforums.com/t...cs-added-pic-heavy.272745/page-3#post-1800335

This is round 2; 60# in the smokehouse. Just added more wood and bumped the temp. to 130*.

 

[daveomak]

Nice.... Very nice....

 

[indaswamp]

Dave, I barely had to touch the needle valve today. I'd watch the top therm. inch up...141.5, 141.7, 142...
And then within 5 minutes, the INT would go up 1~2 degrees. The smokehouse kept a constant +30* on the INT all through the smoke. Just chugged along slowly walking up the temps. It was an awesome smoke day today! Even in the wind!!! When she got to 168*, I cracked the fire door open to stabilize the temp. in the smokehouse until target INT was achieved.