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Where put fan for Vertical RF

post #1 of 23
Thread Starter 

I am having issues with temp control in my VRF smoker.  Top is staying way to warm.  My smoker is a wood design that is very well insulated and the firebox has steel above it with concrete board and tile with 7 x 2 side channels to the top. I know I have a LOT of mass so I preheat before smoking for 30+ minutes but I still see a 20-30 degree difference.  Bottom exit in food box is a 3" opening and food box is ~ 28W x 44H x 22D.   I am thinking a bit of convection air may help.  I also considered adding a couple ports to the bottom of the side channels


  Any ideas or comments appreciated.   I like to smoke a lot at 150-180 for my sausage stuff and the wide range of temps is a pain at the moment.



post #2 of 23
Thread Starter 

I needed to add another item for consideration to my problem.  I am wondering that I have too much insulating material above the firebox with the concrete board and tile.  Maybe cutout a 24" x 16" section to allow the metal top to be exposed thus allowing more convection heat transfer at the bottom.  I am getting good smoke at the bottom just poor heat.  or just add a fan or both.   I almost wish I would have stayed with my old design of just plain vertical.   Last batch of sausage I had to rotate 3 times and then had to run a higher temp at top than I like.   

Anyway just grumbling a bit this AM.   Been experimenting with Salami and sausage recipes and last batch was so so.  Like to find a good sweet and spicy italian.  Family was just so so on the hungarian and standard polish.  Salami was good but a bit too hot.


Cheers to all and this forum is great.  Thanks to everyone



post #3 of 23
I can't see the ducting channels... what is your design....
post #4 of 23
One problem I see is..... You have no way to move air from the FB to the CC without adding air to the fire and making it hotter..... add some air inlets to the top of the FB door... drill a few 1" holes to start... check the flow... Drill them where adjusters can be added...

2nd... If the round hole is your exhaust, it is not big enough and isn't moving enough air.....

post #5 of 23
Thread Starter 

I'll show you a different pic.  They come from the bottom and up each side.  approx 7" wide x 2 ".   They exit near the top.




post #6 of 23
Thread Starter 

HMMMM   Re the exhaust.  I have a 3" exhaust at the bottom of CC and that is what I have seen on other smokers of this design but maybe they don't manage as well.  


Adding more holes to FB -  The Intakes I have now seem to work fine for managing the fire.   I have to throttle them down to keep heat down now.  If I add holes I agree that it adds more air in but won't that make it difficult to control.   I have opened the firebox door to see if that would help and it just makes the fire get hotter which is not a problem.  Adding another exhaust is doable just a pain.   


I was looking at opening the bottom of the CC and maybe adding a few holes there.  I noticed the horizontal RF boxes have tuning plates to help adjust amount of smoke but it is not the sane as the vertical.


post #7 of 23
The exhaust should be as big as the 2 inlets combined for good air flow....

The holes at the top of the FB door, will allow for better air flow through the smoker... adjust the smoker temp with the air to the fire and upper air vent air flow.... like this regular smoker uses for air and temp control.....

post #8 of 23
The center exhaust channel is the size of the 2 inlet channels combined.....

The pictures are not to scale.... sorry.....

....click on pics to enlarge....

NOTICE.... the channels are inside the insulation to maintain heat for convection air flow.... If that is not done, a cold air dam could result..

Edited by DaveOmak - 12/30/14 at 6:01am
post #9 of 23
It would be nice if you showed all of the parts of the smoker... exhaust, inside and outside... heat tubes to the CC inside the FB also... what type of plate between the FB and CC.... trying to figure out where to make adjustments is impossible if all the parts are not included...
post #10 of 23
Thread Starter 

Hi Dave -  Thanks for the great input.  I think your latest pics have helped me.   I see two things that are causing problems at the moment.


1.  My intake air intake has 2 large openings 3 x 3.  so wide open I have ~ 18 sq in area of intake and the exhaust in CC is a 3" pipe which has ~ 9.5 sq in area to vent.     Not a good match and explains why my best smoke is with vents 1/2 open.


2.  My Smoke exhaust chambers from the FB are on the sides of the CC.  The smoke exits at the top of the box on each side from 2 1/2 x 7 openings.  That's 30 Sq in area of smoke exhaust to CC and only the 3" pipe exhaust from CC.


Thus I think the main issue is the Exhaust is way too small.   Now I can add another 3" exhaust or increase the D of the existing.  Either will be a pain as I have everything insulated and tile boarded but doable.   


I also think I need to reduce the size of the smoke chamber exit size at the top.  Maybe Aluminum tape off by a half.  Would like your opinion on that for sure.    Just getting way too much smoke volume and respective heat.   This also begs the point of adding a couple ports from the side smoke chambers ~ 1/3 from bottom of CC.  Maybe create a venturi like effect to help with circulation.


ALSO -  I tried to draw a better pic of the mechanics of the Smoker to help you understand what I have done.  Sorry about the scale not being the best.

 Adding more holes to door is a pain as well as it is 1 1/2 " thick with insulation between 1/8" skins over tile board.   But I need to get this working better.  Adding a fan is not preferred if possible.  Just a thought about mixing up and moving the air to the bottom with a fan at the top.

post #11 of 23
Thread Starter 

OOPS frogot to say CC is ~42" high inside.   Nice size box so I want use all of it.  And I want to HANG sausage not lay it down so temps are even

post #12 of 23
First thing I would do is make the exhaust channel 2 1/2 x 14 to 2 1/2 x full width of the CC...... Using the slide dampers on the FB door will control the temp.... Somehow, add air inlets near the top of the FB to allow more air to flow through the CC while scavenging the heat from the FB.... over time, you will learn how to control the CC temp with the 2 sets of air inlets..... It doesn't matter how tough it will be to add those mods.... the smoker doesn't work well as it is.... You will be happy once you get the mods done....
post #13 of 23
Thread Starter 

Dave,  Is the exhaust channel you are referring to the CC exhaust (3" duct) or the smoke "Channels" from the FB up to the top of the CC.  The smoke channels are on each side of the CC and come from the fire box.  They are 2x7.   The CC Exhaust that I refer to is the 3 " duct at bottom of the CC.   That is the one I thought I would attack first and enlarge.   I am a bit confused as why I would enlarge the Smoke Channel as they put out a ton of heat and smoke.   And I think I have a way to add holes to the door.    




post #14 of 23
Is the exhaust channel you are referring to the CC exhaust (3" duct) B]....... YES
Tear off the back wall and install an exhaust channel and insulate it... The inlet to that exhaust channel, I would make full width 3" high....

post #15 of 23
Thread Starter 

Hi Dave,  OK -  Not sure how I can do the back wall that way but I get the point.  Need to sleep on it to see how and what I can do.  Removing back wall is not trivial.   I did get some holes in the door today.  I'll send a pic when I finish with the slide cover for them.   Have 3   openings at top.  Each is 1.5 x 4.   Doubles the air available for intake.  If I do the math that says I need at least 36 sq in of exhaust area available.  If I do the 3" exhaust that gives me double the area for exhaust vs intake.  Seems excessive  however I could install some type of damper to adjust in the exhaust plenum.  


The back wall has a couple studs that are 16" on center.   If I build the exhaust between the studs that would give me a 3 x 14 opening for the exhaust and I would still have some structural integrity.  that would be almost 50% wore exhaust area than intake.  that would leave about 6" to the side walls.   I think I can find a (3 or 4) X 14 furnace elbow.   Once I get the exhaust outside of the CC I should not need to insulate the actual vent as long as the CC remains insulated (except where exhaust exits).   Does that sound reasonable?



post #16 of 23
the exhaust will be controlled by the air intakes in the FB.... as long as the smoker is air tight..... really air tight....
post #17 of 23
Thread Starter 

Happy New Year Dave,  


Ok - I have slept on it and read more about exhausting principles and such.  The plan for the exhaust is to cut the back where the current 3" round exhaust is located and create at minimum a 3" x 14" opening.   Make a large 90 degree after it exits (I have smoker near a block fence).   Then extend the 3 x14 or ?? up the back until it is above the smoker a few inches.   Make a damper to adjust "if" necessary and some type of cap for looks.     I know galvanized is a no no in the CC or FB however I may have access to some 3 or 4 x 14 plenum pipe that is galvanized.   Using galvanized for the exhaust ??? OK??   If not I can make it all with sheet metal.  I will also wrap the exhaust with some fiberglass.

Naturally my wife just bought 6 racks of ribs for me to smoke this weekend!    I will send some pics as I work my way thru the modifications.  Can't wait to do a temperature run with 4-5 probes to see what happens.


 Bob in AZ

post #18 of 23
Galvanized exhaust is fine.... It's "down wind" from the food.... On the coldest part of the smoker.... and it needs about 700 degrees or so to burn....

Remember to insulate it very well.... It needs to be at smoker temp so a cold dam doesn't hinder the exhaust flow.... A cold dam is where the air gets colder and heavier than the "system" air.... Because your system is a convection flow... (hot air rises) it needs all the help it can get....
post #19 of 23
Thread Starter 

Dave -


Yes,  I am aware of that.  Picked up metal at HD today and found I could get some Aluminum  to make the exhaust for almost the same price and it's easier for me to work with.   Just need to fabricate the transition and plenum as I want the plenum to be full width to the exit point above the smoker a few inches.   When I cut the back I'll see how wide I can go.  That's tomorrow.    Insulation will be some Foam board and then some insulation wrap.  Probably cover that with some siding to make a chase if I have the room.   Down here in SE AZ I don't have as much of an issue with real cold but it still gets chilly.  


Thanks again Dave and I'll keep you updated on my progress.




AZ Bob

post #20 of 23
Thread Starter 

Hi Dave,  Well finally 90% finished mods.  Still need to box flue plenum/insulation and come up with some type of damper- cover for top.  -   I plan to do Temp run tomorrow while I am boxing the Flue/Insulation.  Have 4 probes in CC to check.  SInce I am not familiar with the additional FB holes  - do I start out the warming procedure with everything open or just the main FB openings.   Cover Flue 50% to contain heat some.   ie is there a recommended process to use in start up of these RF Smokers?   BTW -  Final Opening  for flue was 2 5/8" x 17".   Also - added pic of one side on CC where Smoke Channel exits.  I added some "Batwings to see if it will help as well.      See Pics Below    AZ Bob





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