RF sized according to calculator, major hot spot on the other end AWAY from FB!

[rikun]

Hi all,

I've been using my 160 gallon RF for a few years now. It was sized according to Feldon's, but generously so that every major measurement was made 1.5x what the calculator said. I also added upper air inlets later on.

Here are the stats:

Cook chamber size: around 5.5 feet x 24.4" (straight section without accounting for the curved end) a little bit thicker than 1/8"

Tank CC volume: 163.3 gallons

Firebox side %: 108% (23" x 25" x 24") 5/16" thick

Throat area: 140 square inches

Area under RF plate: 140 square inches

BP gap: Slightly larger than 140 square inches (not by design)

Stack size 5" pipe, 30" inches above CC

Air inlets: waaaaay oversized, running them most of the time around 70% closed.

I think everything should be close enough to not cause any problems... But:

I seem to be having a problem that nobody has, the other end of the smoker where smoke enters the CC is almost 100F hotter than the FB end! The only time both ends are even, is when my wood has just burned down and the heat from the smoke has gone, but there is still residual heat on the BP. I also did try to reduce the hotspot on the upper shelf by welding on a plate in to block the airflow to top shelf (check out the pic). It worked, but it just shifted the hotspot lower. I guess I should remove this plate, since it doesn't do me any good.

Temps have been mapped by Thermowork probes, there's a clear gradient of hot - cooler - cool from CC to FB sideways. Could this be because of not enough draft? Air moving so slowly it has time to cool down too much when it reaches the FB end?

I have three grates and four slides in there, so the slides potentially might restrict the airflow a bit.

My fire burns well, clean and splits ignite nicely. Only problem with my fire is that I seem to be losing my coal bed, but I've kept it going by adding lump and still get the same hot spot. I actually get the same temp gradient with using just lump without any wood. Food generally tastes fine out of the pit.

My doors leak a bit, but I've ran the cooker for around 6 hours empty with both doors 100% leakproofed with foil tape and it made no difference. Also, the upper air inlets did nothing.

I have to add, adjusting the nose of the cooker up or down doesn't seem to have any effect on temps, at least within reason.

Any suggestions? I'm very close to giving up on this smoker, since I can't wrap my head around what's causing this much temp variation...

I've added some pics also to give a better idea of the smoker construction

Slides and the baffle on top shelf (BP to CC opening end):

.

slides_cc_end.jpg

• rikun
• Dec 5, 2016

Slides (middle):

slides_fb_end.jpg

• rikun
• Dec 5, 2016

Early construction, showing bottom intake pie vent (there are two more at the door, one slightly higher than the fire grate and the upper air inlet way higher):

inthemaking_1.jpg

• rikun
• Dec 5, 2016

 

[bgingras]

are you level? I find my temps tend to fluctuate a bit if I change the level of the unit. meaning if I raise the end opposite the firebox a bit, it will get hotter. if I lower it a bit, it will run cooler. I had to experiment to find exactly where on the "bubble" the smoker needs to be to heat evenly.

 

[ahumadora]

How thick is your reverse flow plate?    

Also how much room do you have at the end of the tank where the smoke makes the turn?    Wouldn't be too hard to shorten the RF plate a few inches to see if that makes a difference.

Whats the plate above the guides?

Do you have any more 5" pipe where you can add 12" or so easily while running to see if that makes a change? 

 

[rikun]

1/4" baffle plate.

Around 7.8" from the centerline, should be equal to the throat area. I was thinking of making it smaller... I don't think shortening it would help any, and that would mean making a new drain...

The plate above the guides is as explained, I tried to remove the hot spot with it. It sort of worked, my upper grate now has no hot spot, but it just shifted down...

I already tried with long ass temporary 5" pipe added, made no difference.

I've tried it level, nose up, nose down, etc... But I can't be sure about that, my grates, BP, firebox and stack would all need a little bit different levelling since they're not 100% square lol. Also my BP slopes a bit to the drain at the other end away from firebox. Should I try to level my smoker so that my BP is 100% level? That's one thing I haven't done and would raise the cooking chamber up quite a bit.

And I haven't found any difference with levelling, although it might be that I haven't found my smoke's "bubble" if such thing exists for it...

 

[bgingras]

I've found that my smoker will run hot on the fire box end when I drop the opposite end just below level. when I lift the opposite end to be a degree or 2 above level things even out. If I raise to high, I see the opposite effect and my fire box end will run cooler.

 

[rikun]

Thanks,

As said, to this date I haven't found leveling have any effect on my temps... But I'll keep working on it.

Where do you measure that 2 degree level? Grates? Baffle plate? Just general level on the trailer?

 

[bgingras]

For me it was literally placing a level on the top of the cook chamber. My RF plates pitch towards the center drain. To me, it sounds like you are not getting a good draft back from the opposite end from the fire box. This, to me anyway, suggests that the cook chamber is tilted upward away from the fire box. How far into the cook chamber is your flue pipe?

 

[rikun]

It goes down about 2-3" and I've cut it on a 45 degree angle to try to reduce the friction with the air exiting it.

I can tilt my cook chamber as much down as I want and still the heat distribution is the same.