Need some help with my revese flow smoker

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miket

Newbie
Original poster
Sep 5, 2011
19
10
Hi,

I built a reverse flow smoker - loosely based on the lang 36.

Only made the drum 18" diameter and 36" long
Firebox is 14.6" x 14.6" x 14.6"

The question comes with the baffle plate - that is a touch higher than what I wanted, so the flow area underneath the baffle is a bit bigger than what the xls calc sheet calls for although I made the restriction at the end, where the baffle ends - very close to the correct value.

The entry into the firebox is as large as the area under the baffle plate (quite a bit bigger than what the xls sheet calls for).

Would it be better to decrease the hole from the firebox to the recommended size, or is it OK to have that too big and have the baffle plate end be the restriction ?

Thanks
Mike
 
th_dunno-1%5B1%5D.gif
 good question I think it would be fine,  It should still have the same flow.  Don't know is it will do anything to change the heat though.
 
You didn't say if it was finished or not??  I'd just try it as is and see how  it works.  Let's see some pictures!  
biggrin.gif
 
Ok, made some measurement and did some calcs.

The xls spreadsheet calls for a firebox to cooker opening area of 24.74 sq inch

What I actually have is 35.54 sq inch

And the area at the end of the reverse flow plate to the end if the drum is 28.28 sq inch

I am struggling to get enough heat in the system and it is real heavy on fuel :-(

What is the recommendation - reduce the firebox opening ?
 
You didn't say if it was finished or not??  I'd just try it as is and see how  it works.  Let's see some pictures!  
biggrin.gif
Finished - tested it - it works OK, temp from one side to the other is about 5 deg F difference, but really struggling to keep the temp up, and using allot of fuel :-(

Some pics :-)

7387f1ab_IMAG0241.jpg


d3f72c1a_IMAG0242.jpg


f6c6f73f_IMAG0243.jpg


0feb9ed5_IMAG0245.jpg


89d78881_IMAG0240.jpg


40fd3b1f_IMAG0246.jpg


7e59ac07_IMAG0239.jpg
 
What size is the air intake into the firebox?
Sheet calls for 9.28 sq inch

Made the inlet 14 sq inch - seeing that they are adjustable I thought that some extra would not hurt :-)

I have posted some pics, but that is held for moderation - so should be up soon.
 
This , and what is your smoker made out of ?  thinner mat'l does not seem to hold heat as well, but should be fine at 225 what temps are you going for?
Hi,

Firebox is 0.2"

Rest of smoker is 0.12"

Reverse flow plate is 0.08"

One the test run I was doing some ribs and a pork but at 250 - and it took some work keeping it there.

Fuel - I started with brickets but switched to lump after a while - was easier with the lump.

Pics are on its way, but post is being moderated.
 
here is the xls file i used for the calcs

chimney inside diameter is 2.84" and is 24.41" long

99233f97_xlscalcs1.jpg


f484459d_xlscalcs2.jpg
 
Mike the only thing I can see being a problem is inadequate intake/exhaust.

Next burn do me a favor and raise your firebox grate above the intake, so the air comes from underneath the fuel.

I am pretty sure your intake is undersized.

Is your reverse flow plate on an angle, if so try angling the exit end up at level or higher than the firebox end.

Are you running your exhaust full open, give me a couple more pics of that exhaust, it may be undersized as well.

Although your calc calls for under 3" diameter for exhaust I would suggest 4" diameter.

But I really believe the problem is your Intake.
 
Mike the only thing I can see being a problem is inadequate intake/exhaust.

Next burn do me a favor and raise your firebox grate above the intake, so the air comes from underneath the fuel.

I am pretty sure your intake is undersized.

Is your reverse flow plate on an angle, if so try angling the exit end up at level or higher than the firebox end.

Are you running your exhaust full open, give me a couple more pics of that exhaust, it may be undersized as well.

Although your calc calls for under 3" diameter for exhaust I would suggest 4" diameter.

But I really believe the problem is your Intake.


Hi, thanks for the assistance.

No the plate is level

The picture only shows one intake - there is another one exactly like that on the other side as well.

Would it help if I make the firebox exit a touch smaller - more into line with the spec sheet - restrict it at the top - that way the reverse flow plate ends up being higher than the firebox exit ?

Something like this :

e5fbfc5c_IMAG0246_mod.jpg


From some quick calcs I need to reduce the firebox opening by 0.8" at the top - would that be feasible ?

Would the bigger exhaust not make the system even more fuel hungry ?
 
One more question on the exhaust/chimney.

I see every body always advises to keep the chimney wide open - so is a damper even required - or can I just skip that and go straight through chimney.

With the 4" chimney you advised - what length should I make it then ?

Thanks

Mike
 
But I really believe the problem is your Intake.


I took some measurements and did some calc there is two intake wheels like the one in the pic - area for each wheel is 7.9 sq inch - so the total intake is 15.8.
 
Hi, thanks for the assistance.

No the plate is level

The picture only shows one intake - there is another one exactly like that on the other side as well.

Would it help if I make the firebox exit a touch smaller - more into line with the spec sheet - restrict it at the top - that way the reverse flow plate ends up being higher than the firebox exit ?

Something like this : I don't think that would help, as long as your inlet into the chamber is at or below the plate I think this should be ok.

e5fbfc5c_IMAG0246_mod.jpg


From some quick calcs I need to reduce the firebox opening by 0.8" at the top - would that be feasible ?

Would the bigger exhaust not make the system even more fuel hungry ?

This does have me baffled, I would thing am undersized intake and exhaust would choke the fire.



One more question on the exhaust/chimney.

I see every body always advises to keep the chimney wide open - so is a damper even required - or can I just skip that and go straight through chimney.

With the 4" chimney you advised - what length should I make it then ?

I would do the chimney as a last resort, because its a completed project, if all else fails maybe we can explore that route later.

You have to remember there's not an exact science to these formulas, for example you couldn't run 2" pipe at 6' for exhaust, there are other considerations such as head pressure, If this was a new project I would say go with the largest diameter like 6" and put in a choke.

A lot of folks use a damper or what some refer to as a weather cap, but its nice to have if you ever want to choke down the pit like when "weeping ribs"

Thanks

Mike



I took some measurements and did some calc there is two intake wheels like the one in the pic - area for each wheel is 7.9 sq inch - so the total intake is 15.8.

Are you including the entire hole or the area circled below? Mine runs at a minimum of 18.85 (2 valves fully open)


f3d99960_640x382px-LL-f6c6f73f_IMAG0243.jpg


54e13955_Picture18003.jpg


For now I would just raise the fire grate above the intakes and do a test burn, take the least invasive approach first, just prop up with something, just be careful if using cement products as they may explode or shatter.

af9f4721_640x382px-LL-0feb9ed5_IMAG0245.jpg
 
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