BBQ Pit engineering question..

Hello, I built a custom BBQ pit myself awhile ago, and have since made some modifications. I posted some pics of the new mod, the old pit pics are on here somewhere about a year ago. My problem is I have problems keeping the temp up to my target temp, 250-275 in the cooking chamber. I converted my over under BBQ to an over under - offset BBQ. Probably the only one to have such a beast. The reason was, the over under was always too hot for low and slow. So I converted the storage chamber to the left as the pit, as I originally planned to do, but was too lazy to go through with it at the time. So before, I used an open draft system, had a fully open chimney and a draft air inlet control in the pit chamber. It worked ok, but ran too hot. So I converted the BBQ to an offset design. But, I also added a new pit temp controller, and it works fine. You can see the copper air intake tube, bottom left of the pit, that the blower attaches to. The problem is that in the top cooking chamber, on the right in the pic, it never gets to where I want it at 250. I have the control temp probe about 1 foot from the top of the chamber. I also have quality analog probes in place and they all agree. I would like to know if anyone has any ideas on how to improve this. Should the chimney be closed down with a damper when using a power draft to keep the heat in. Vs. an open draft where you want full flow out for heat and airflow in . . And with such a vertical pit, where do you think the best place to measure temp for the pit controller should be. It varies tremendously every 6 inches. I even have a analogue dial in the chimney which sometimes runs higher than the cooking chamber...

Actually I think I realize the problem. I will just tear it down and start over !! My wife always says, you never get it right on your DIY projects, until the third try.. LOL.. This will be my third try.. It does seam to be a historical fact for some odd reason..

Thanks. I screwed up the design so I'm trying to salvage it. Some good questions so maybe more can help. The pit temp, on the left lower door, runs hot as expected from a burning wood fire, 500' roughly. I have an analog probe in there. The blower runs most of the time and the wood I consumed last night was insane, a ton. So the fire, air and heat are being produced as needed in the pit. I planned this design to use with a blower only, as there are no air vents present, just the 1 inch metal tube through the wall of the pit for the blower. So its definitely airtight. The grill racks are on the right. About midway in the top metal door is my therm probe, about a foot from the top of the chamber. Probe enters from the side through a hole drilled in the cement. I also have an analog there and the temps are consistent with each other. I can not get that temp to get close to 250' at all, it stays at 180-200 ' , even after burning a ton of wood and the pit temps going 5-600 ' So the problem is I cant get any heat to where it needs to be. I do get great smoke, it would be a great cold smoker, but I don't have the patients to BBQ a chicken for 10 hours, like it took last night. A few of my ideas, please chime in. The meat chamber is too tall, the smoke gets cold by the time it gets to the grill rack. I did dampen the chimney, it just seamed to make it smokier, not hotter. Or, maybe I just suck it up and move the fire box back to the right lower door area, that is where it was, but then it ran too hot. I wanted it to be offset. I could put an aluminum sheet metal insert to guide the heat from the firebox up to the grill rack also. One last point, the entire pit / grill combo is cement and firebrick, so even with the fire blazing , the top of the cement fire pit on the left doesn't even get hot, the thermal mass must be overwhelming as well. Very lost at this point. Thanks.

Just BS said:

What's "too hot" (when the fire is below the food)?

Different foods cook at different temps ~ use both. If it's too hot, you could use a heat diffuser or maybe some type of tuning plate.

Fire bricks on the bottom and up the sides in both chambers? How big is your opening between the offset and the pit?

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Thanks, I think those are the issues I will try, the opening could be bigger, I sledged it out bc is was a solid cement wall before. I'm guessing about 1 ft by 18 inches. I was thinking of the firebricks as well, to narrow down the cooking chamber. Too hot was 350' with a broken pizza stone as a diffuser. Thanks for the tips, I'll keep experimenting.

Thanks dudes. I think Dave may have got me thinking WTF did I try to convert it to an offset, I should have just tried to figure a way to tame the fire down with the over under. I got on a kick about all these cool offsets and said, hey I can still do that. lol. Thats me, overfixing everything. Thanks for the advise everyone. I will experiment today. I may use it as a combo by shifting wood from under , to the side based on heat or something like that.

BigBellyBBQ said:

think about the heat asbortion rate of a masonary build and in my opion, the fire box should be sealed with plate and under your main cooking chamber because as you stated "consumed a large amount of wood.." you must keep flues open....the steel plate will help transfer the heat and the masonary will protect / insulate..I used 1/2" boiler plate in mine.. if you have a 500 fire box and cant hold 250 tells me you are not efficient in transfer...smoke really does not cary heat unless your moisture is high..ghood luck..

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Ok, thank you, I think you are on to an answer, but please explain to me in detail what you mean. Are you saying that I should line it with metal on the interior. I was thinking about that, the fire now just goes straight to the brick and cement with no radiator deflector. Would a simple sheet metal deflector keep temps inside rather than absorbing into pounds of cement and brick ?

mallorjc said:

I like the idea of fire-box reflective insulation from heat absorption by the brick and think you should consider the 1" tube being too small to allow proper flow / hence cold smoke at top of cooking chamber. This just looks too "almost perfect" to tear down!

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Thanks, no I'm not tearing it down, that's just my frustration anger speaking. I don't have the energy to tear it down anyway after building it for over 2 years, lol.. The one inch metal tube is for the IQ110 blower attachment. I built this pit with the full intention of using a blower only, no free drafting. So yes, without a blower I would have to crack the pit doors etc, but I like the blowers, used them for years and so I custom built this pit with that in mind and no air leaks with additional vents etc. I also used to have a Kamado #7 , ( sold it after re locating ) and that is the style I tried to replicate here, with little airflow, less fuel consumption and stable heat. Obviously I am falling short on that part. I have high heat and large fuel consumption, as the blower manifold I built into the pit area is really driving a big fire, but as mentioned, the transfer of heat is way off. So as Big Belly suggested, I will put a metal liner in the firebox and attempt to direct the heat more laterally to the cooking chamber. Will let you know how it goes.