Need some help with my revese flow smoker

[fourthwind]

Ok here is my two pennies worth of input.  As a general rule you want double the inflow as you want the outflow.  Since you are using 3 inch pipe you have about 7 sq inches, so you have those numbers if your inflow is 15.  What the excell sheets dont tell you in the gap on the end of your plate which should be the size of the outflow (in area) times 1.3, so it should only be about 10 sq inches.  If I had to take a guess, the amount of airflow you have is too high, and your energy is going right out the pipe and not into the metal.  One way to maybe measure that is to mount a temp probe in the higher section of the cook chamber and see what the air flow temp is looking like.  Which brings me to another question.  You said the length of your stack, but is the inlet to the stack at the top of the cook chamber or down by the first grate level? You are also a little skinny on heat mass. (Thin Metal)  It's going to take more energy to keep the system warm.   I didnt read what type of fuel you are using, but you might try a higher grade of coal or wood.  Just make sure if you are using splits that they are fine splits or pizza wood.  It will be more efficient for a smoker that size.

 

[sqwib]

Fourthwind, I actually thought the opposite I think with his stack size and intake location, hes not getting proper draft.

I could be wrong but the firebox to chamber and the gap on the end of the reverse plate are not THAT critical unless undersized.

I am not disagreeing I just want to make sure that Mike knows, this is gonna be a trial and error thing.

Mike if you look through the open vent when you have a good fire and sees that the fire is burning straight up and not towards the smoke chamber slightly, I would say its definitely a draft problem. It will look like the fire is being pulled in under the plate.

But please please take everyone's advice and approach with the least invasive approach, don't start hacking that thing up.

I would definitely do the thermo like Fourthwind said, just make sure to use a calibrated (tested) thermometer

 

[miket]

 Which brings me to another question.  You said the length of your stack, but is the inlet to the stack at the top of the cook chamber or down by the first grate level?
 

Hi,

Yes, the inlet to the stack is at the top of the cooking chamber.

Currently the level that the plate is at - is 15.95" wide - so the plate is 15.95" wide, and the plate to the end gap is 1.77"

So if I understand you correctly, you recommend that with the stack having a inside diameter of 2.84 that the gap at the end of the plate should only be 0.52" wide ? that would give it an area of 8.294 and the stacks area is 6.33 ....... 8.294/6.33 = 1.31

And you are of the meaning that the stack is correctly sized for this application ? or at least should work fine ?

 

[miket]

But please please take everyone's advice and approach with the least invasive approach, don't start hacking that thing up.

Yip - thanks - there is plenty of experiments I will run this coming weekend :-)

Also listening to every bodies input and trying to learn as mush as can - there is always more than one way to skin a cat.

 

[miket]

Maybe there is one piece of info that I left out :-)

When I seasoned the smoker - I used some wood pieces and the fire drew just fine - temps went up to 400 no problem.

Issues stared the next day when I decided to do a cook with charcoal briquets - even with the vents fully open temps seemed to hover round 250 odd, and I used allot of briquets, I then switched to lump charcoal and things improved, but I still went through allot of fuel, and temps were mostly round the 250 max mark.

The meat also had a rather heavy smoke taste - a bit more than I would have liked. Smoke was added via hickory chips that was soaked en I then put directly on the coals.

If this info helps determine the cause.

 

[alelover]

3 inch diameter is 7.1 sq. in. So 14 sq. in intake would be around 4 1/4 in diameter. I think because the intake is above the fire it is pulling the heat away to quickly and not allowing the coals to ever get hot enough. Does that make sense?

 

[fourthwind]

Hi,

Yes, the inlet to the stack is at the top of the cooking chamber.

Currently the level that the plate is at - is 15.95" wide - so the plate is 15.95" wide, and the plate to the end gap is 1.77"

So if I understand you correctly, you recommend that with the stack having a inside diameter of 2.84 that the gap at the end of the plate should only be 0.52" wide ? that would give it an area of 8.294 and the stacks area is 6.33 ....... 8.294/6.33 = 1.31

And you are of the meaning that the stack is correctly sized for this application ? or at least should work fine ?

An easy experiment would be to just put a piece of metal off the end of the RF plate and choke off some of that extra space. Since you made the stack long enough, it should work fine.  dropping the internal stack level down to the grate level will change the internal airflow and the flavor of your food.

The other info regarding it heating up with wood tells me a little.  Wood gives off a lot more energy than charcoal.   If the charcoal you are using is not good quality you could have issue's there as well.  Lump or not.  If you think the air vents are too high, just put your grate on stilts for a burn and see what happens.  The heavy smoke flavor you got when you put wet chips on coals is a whole other story.  Hickory does not do well when smoldered.  You want it to be burning.  You want that thin blue smoke or none at all.

 

[miket]

Right a update, lifted the grid - no difference.

Opening the door a touch - no difference.

Tilting the cooker - firebox down - no difference.

Then I added a plate to the end of the of the baffle plate to restrict flow - it made it worse.

So if I am reading it all right - I need to go to a larger diameter stack ....

 

[sqwib]

 and the plate to the end gap is 1.77"

Right a update, lifted the grid - no difference.

Opening the door a touch - no difference.

Tilting the cooker - firebox down - no difference.

Then I added a plate to the end of the of the baffle plate to restrict flow - it made it worse.

So if I am reading it all right - I need to go to a larger diameter stack ....

I reread this post many times.

And after your last few post I still believe its a draft problem and part of the problem may be the reverse flow plate restricting the flow, I think Frank has about a 6" clearance from the end of the reverse flow plate to the wall  of the chamber.

Keep on trucking You'll get  it.

 

[miket]

Update time :-)

Right - I removed the old chimney and replaced with the new 4 inch model :-)

Grate level in firebox is back to original level - fired her up with the exact same charcoal as I did last time round - I struggled to hold 225 last time round - this time, with only the chimney changed - thing look allot different :-)

Was still climbing slowly, but I shut her down - will do a pork butt and brisket tomorrow and see how it works out ....

Thanks for everyone that chimed in, it worked out for the good.

Cheers

Mike

 

[fourthwind]

Looks awesome Mike!  Make sure to test that thermometer every now and then in boiling water.