# Fridge Conversion Chimney Placement



## dangerdan (Oct 4, 2008)

I'm currently working on a fridge conversion. This is my third fridge smoker over the years and the last two had the chimney cut into the top. The last one really never even had a chimney, just a hole in the top of the fridge to let the smoke vent. 

My question being, is there any benefit to running the chimney out of the back of the unit rather than the top? I've seen them both ways and would like a little input before cutting into the back of my current project fridge. 



The small circle shown in this photo is from where the fridge light was installed. If I do cut an opening the bottom of the cutout would be at the bottom of the small hole. I'm considering a 5" to 6" cut-out as I'll be using a firebox from a chargiller for thie offset firebox. It would line up between the first and second shelves. The shelves are 8" apart.


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## richtee (Oct 5, 2008)

Honestly Dan... I'd stick with the top and pop rivet or whatever a plate over the little hole. The heat/smoke will partially bypass the upper rack if you vent it below them, not to mention possibly creating a "stale smoke" pocket above the vent. I'd also center the stack in the top. A short length of pipe will help the "draw" of the smoker, in effect as a chimney does to a fireplace. Plus, you can damper it to keep out the rain/whatever when not in use, or tweak it for temp/smoke control.


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## dangerdan (Oct 5, 2008)

Yeah, thats kind of what I thought too.. Just double guessing myself before putting it in. 
Think twice cut once type a deal or something like that eh? 
I also still have the old damper plug from my Chargriller. I can install it inside the fridge and use it for a secondary damper to control heat if I need to. 

Hopefully this one will last longer than the other two. Fridges don't grow on trees anymore...

Thanks..


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## tn_bbq (Oct 5, 2008)

Ever thought of doing a reverse flow smoker?  Let smoke enter towards the top & exit from the bottom?   It would require some extra channels and/or pipes, but that system works great with my Backwoods Smoker.


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## richtee (Oct 6, 2008)

Hmm...really? What model? Seems like a strange setup, working against convection and all... is there a fan or something?


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## white cloud (Oct 6, 2008)

retracted.


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## tn_bbq (Oct 6, 2008)

Backwoods Smoker

_Teams using Backwoods Smokers have won all the major competitions, Memphis in May, the American Royal, and the Jack Daniels Invitational._ 

http://www.backwoods-smoker.com/

They do offer (for a price) a convection fan option. Most folks don't go that route. I suspect if I did professional catering I would consider it.

Basics:

Double wall, vertical, water-pan, reverse-flow BBQ smoker.

The cooking chamber is separated from the firebox by the water pan. The heat/smoke flows up the sides of the cook chamber and actually enters the cook chamber from the top. The chimney inlet is in the lower back section of the cook chamber. 

So, your cooking chamber is heated from all sides. In addition, the Backwood Smokers have insulated double walls that hold heat very well.

I'll post some pics.


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## richtee (Oct 6, 2008)

Ahh  OK. I did look them up. Interesting concept. I guess the heat/smoke has to go SOMEWHERE...even if it is against the normal flow of things.


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## tn_bbq (Oct 6, 2008)

These things cook some serious BBQ. 



That 1 inch gap at the top is the heat/smoke inlet. The heat/smoke runs up the entire side & rear of the chamber.



Closer view:






Chimney inlet (looks like Swiss cheese)


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## richtee (Oct 6, 2008)

Well, cool. I got it now...thanks for the pix!


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## white cloud (Oct 6, 2008)

I just seen two of those last weekend and have been considering a build myself. That is pretty cool how it works. Now it gives me more to consider. Thanks for the info


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## tn_bbq (Oct 6, 2008)

The heat/smoke definitely goes SOMEWHERE in a Backwoods Smoker (BWS).

Folks modify their offsets in a similar fashion by lowering their chimney intakes with ducts/pipes, etc down to the cooking grate.

All I know is the BWS is a mighty fine smoker with a proven track record on all the competition BBQ cooking circuits.  You'll probably find one at every competition event you go to.

Whether or not the refrigerator conversion would benefit from such a design is anybody's guess.  I suspect I'd simply put the chimney intake at the top and go that route.  You could always modify it at a later date with some pipe/ducting, but for starters I think I would go with the K.I.S.S. design (what's the fun in building something perfectly the very first time anyway?)


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## davenh (Oct 6, 2008)

Nice looking fridge Dan! I was kinda wondering the same thing about where to put the stack on my build. Center top makes sense. Thanks


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## dangerdan (Oct 6, 2008)

Nice design heating from the outside in and I like the idea of no direct heat in the smoke chamber. Unfortunatley I'd have to dig out all of my insulation and do alot more fabrication to seal the outer shell. Seems like I'm dumpin a ton of money into this conversion already.

I'm considering a pretty wild graphic design on this unit as long as the outer shell doesn't get too hot. I'm hoping to keep outer temps as cool as possible but hot enough in the smoke chamber to still get the versatility I'm looking for. 

This unit will be expected to handle my cooler smokes, bacon, sausage, fish, etc.. If the outer shell doesn't get too hot, the hotter cooks roasts ribs etc. will be ok... 

A lil testing will tell me what I need to know.


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## richtee (Oct 6, 2008)

Honestly Dan... as long as you keep conduction of heat from the heat/smoke source to the OUTER shell at a min...you should be fine. But like we discussed... heat 'er up!


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## walking dude (Oct 6, 2008)

i would maybe also add a fan of some sorts, so the smoke circulates the chamber some before leaving the chamber........if you have TOO much draw from the chimney, some of the meat may not get kissed by the smoke much...........


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## dangerdan (Oct 6, 2008)

The firebox looks a little big to me.. I'm thinkin it's gonna get mighty hot in there..
	

	
	
		
		



		
		
	


	







Some masonry lath and chimney mortar should seal the openin g nicely.



My initial thoughts are to only cut the opening the size of the damper and give it a test run. 



While laying out the firebox position I drilled a pilot hole in the center for an anticipated damper should I go this route. If I don't use the damper I think I'm going to need a pretty good sized baffle across the bottom.

I figure I can always cut the fire box cut out bigger if the smoker temps are too low. Once the hole is cut though, there's no uncutting it...


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## davenh (Oct 6, 2008)

Dan...how are you mounting the firebox, directly to the outer skin with a collar to the inside? I'm just wondering about the heat transfer from the firebox to the outside skin.

I was thinking about mounting mine on some kind of spacers and bracket to keep it cooler.

Any chance you have a pic of your damper setup?

Edit: Guess I should refresh my page once and a while, your pics are already there..lol.


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## tn_bbq (Oct 6, 2008)

Looks good.

I'd say the first half dozen (maybe more) times you fire that thing up will be a "test" run.  That's sorta the deal (fun) when it comes to making your own smoker.  Part of what makes this stuff a hobby.

I think adding that damper is a good idea. Might come in handy should your temps spike up on you.

You've probably already planned on this, but a tuning plate/damper/baffle that separates and shields your meat from the hot coals is probably a good idea too.


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## dangerdan (Oct 6, 2008)

to seal the passage between the outer & inner shells I plan to put in some lathe and then mortar it with chimney mortar. If it doesn't hold up I'll consider another method but with a couple struts from the bottom corner of the fridge to the firebox it should prove to be sufficient.

The baffle is already being cut. I'm using a large diameter pipe (about 16") to cut a strip for the baffle. I stopped by the shop today and had asked about 26" but it was too flat.


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## walking dude (Oct 6, 2008)

dan.........no one SEZ you gotta fill that firebox UP!...........just damper down one or two briquettes, or what ever will be needed to get to temps your require


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## white cloud (Oct 6, 2008)

I wonder if there is a formula for figuring the size of fire box proportionate
 to the cook chamber. I was thinking  this earlier today and was going to ask on the forum


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## davenh (Oct 6, 2008)

Looking forward to seeing what kind of temps you can get inside.


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## dangerdan (Oct 6, 2008)

I hear ya WD. I'll probably cut it all the way out...I was just a little overwhelmed by the sizer of that cutout. My other two fridges only had lil 4" intakes but I've only done fish in the past with them. 

Higher heat/bigger meat..
	

	
	
		
		



		
		
	


	





If I cant get cold smoke out of it I can always add a smoke generator to the other side.


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## walking dude (Oct 6, 2008)

also, if you hadn't cut the holes out yet.........just drill holes.......that will also cut down on heat transfer


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## j0k3r-x (Oct 7, 2008)

I don't think the firebox is too big at all! Rule of thumb, the firebox should be 1/3 the size of the cooking section. I think you might want to cover up that insulation with some sheet metal and get a stick or something and poke that excess insulation back up into the sidewall or maybe pulls some of it out. That firebox is gonna get real hot, you don't want an insulation fire smoldering between the sidewalls of the fridge! Might make your Q taste itchy.
	

	
	
		
		



		
		
	


	





 Looks like it will be a very nice and large smoker when you are done! I love those old refrigerators!

Maybe this will help on your build or anybody else on future builds! You will need Excel to use it.
*BBQ Pit Builder Ratio Calculator*

http://webpages.charter.net/tomchis...files/Ratio calculator/timplate bbq form2.xls


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## white cloud (Oct 7, 2008)

Thanks JOK look like good info. I know someone else started this thread but look how many people gained by it without a slide show.


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## dangerdan (Oct 7, 2008)

I'll second that one. Nice to see those calculations. looks like I'm in the ballpark anyways, Thanks JOC 

I hope to be able to pick up my sheet metal today to get the trim done around the smoke chamber and get the door skinned. While I'm waiting for that I can cut in the chimney and finish cutting the firebox passage.


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## tn_bbq (Oct 7, 2008)

Hurry up, the weekend is just a few days away.

Looks like it's coming along nicely.


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## dangerdan (Oct 8, 2008)

Got a little more work done on the fridge with the firebox cutout finished & sealed, chimney installed etc., and I gave the sheet metal shop a call as I should have been able to pick up my material by now. The guy says well I applogize but I forgot.
	

	
	
		
		



		
		
	


	





 FORGOT? Man I got to get my freak on, YOU FORGOT? lol

Anyhow I figue, this rocks gotta roll so I pulled out the old rubber seal from the scrap box and figured I'd use that for test purposes. I fired up a small pile of coals and got up to a respectable 130* and held that for a while. The temp held nice and steady responding quickly to the outer damper as it should. 






all went well so I figured lets ramp it up a bit and on went more coals.



up goes the temp to 240* and then up further to 270* and continued to climb to near 300*. Being happy with how high the temps were I let things settle back down and added a second probe monitoring the temp ranges to 230*. 





I found a top temp of around 230* to 240* at the top rack hieght while the bottom rack registered a temp at 194*, with a 46* difference between the two areas. However, at lower temps, say 130ish, the temp difference is much less with the balancing range at about 110* with a 7 to 10 degree difference. 

I still need to have my baffle fabbed and installed but I doubt this will change things too much. To achieve a more even temp I think I may need a larger stack diameter. One consulation was that at the lower temps the overall temp difference was less. At higher temps I believe the greater overall temp difference was because the 4" stack just cant dump the heat fast enough. While this doesn't necessarily mean that the I need a 6" stack (yet), it's certainly something to consider. I think if I change the chimney and go to a 6" stack with a chimney damper and it'll be strokin. 

I'll run it for a longer duration once I get the door skinned and trim/seal completed and a baffle installed and see what we see then. 

Overall I'm happy with the way it ran at it's lower temps with a good response to the damper and a nice steady 170ish roll with no fluctuation. Next I'll see what the lowest manageable temp I can achieve and see how that holds. I'm looking forward to cooking some dead animals in this thing real soon.


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## davenh (Oct 8, 2008)

Good stuff Dan 
	

	
	
		
		



		
		
	


	





. 

I think after you install the baffle or water pan it will help with the bottom level temps. Right now you don't have any mass in the bottom of the smoker to absorb and keep some of the heat at the bottom. 

A water pan or baffle would also divert the hot air more to the walls instead of straight up the center. That should also help the smoker heat more evenly.


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