second build : RF with insulated firebox

[Tospy]

Hey Guys,

So after my first build, I got a lot of possitive reactions and some orders....a friend of me asked to make him a reverse flow , with insulated firebox and a grill on top off the firebox.

The main reason for him to insulate the firebox was safetyreason....kids etc. His wishes where a functional rig for a reasonable price, the ability to grill without using the CC and after all it has to be a "easy to move rig"

As I'm starting to make my drawing , I was wondering what you'll think about the grill/searing grate on top off the firebox. IMHO you can use that after your cook in the CC but not during.....Or am I missing things?

CC will be a 90 gallon cilindre , FB inner shell 20.5 x 20.5 x 20.5 inch...

Hope to learn some things about those searing grates/firebox combi's

[towtruck]

If you make a cover plate on top of the fire box that hinges out of the way you can have your bbq grate under there over the fire. You would have to choose whether your grilling or smoking....

I would make the fire box and fire tray for the smoker first and then add shelf slides inside for the fire tray to slide in at different heights for grilling or get fancy and make the grilling grate adjustable. A mini Santa Maria on top of the fire box.

[Dirtytires]

The grill on the firebox is definitely NOT usable while smoking in the cook chamber. The grill area is pretty small, the fire is so far below it’s hard to adjust the heat and it allows yet another area for air to creep in during a smoke and mess us your temps. They always sound good but I’m not sure they get used a whole lot and is one feature I’d skip, especially on an insulated firebox.

If he insists, make sure your seal it well to prevent air gaps.

[Tospy]

Thanks for confirming my thougts....I Think I'd like to propose hime a kind of santa maria grill next to his RF smoker.....hope to finish some drawings soon

[Tospy]

Starting with a plan.....lots of work to do but getting somewhere

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In this design , I want to use 1/4 " sheet metal for inner and outer shell off the fb. Insulation will be 4.5 cm , about 1,8 inch. Cc will be made out off a pipe 6,4mm , about 1/4 " inch and will be 39 inch long....

[Dirtytires]

The outer shell is only to hold in the insulation. It can be much thinner. I used a 12g and it is way overkill.

[Tospy]

There you got a point dirtytires. I'll try to redesign thar.

The drawing os almost ready for this one....

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[dacolson]

Your plans look great, Tospy. I love the cart design. Can't wait to see the build start.

[Tospy]

So....that was a while
Long story short....Covid was a bit of a pain here....been sick for 4 months and revalidating slow. But for now, it's going better everyday so I decided to start the build now.

The guy I'm building this one for , asked me about a warming chamber. Can you use it as a "second" cookchamber but with different temps? Or is achieving the wanted temp in the "warming "chamber influencing the temp in the main cooking chamber to much?

In my opinion it could be an extra cookingchamber but really would appreciate your advice/experience!!!

Hope tot post some pictures soon fromthe build!

[dacolson]

Glad you’re recovering. Welcome back.

If you build the warming chamber over your fire pit, you can run it at different temps separately from your CC if you have a throat and baffle going into it directly from your FB. Since this is an RF build, I’m assuming that’s the plan. Withought the direct opening between FB and WC, your temps are somewhat dependent on your CC temps.

[Big T]

I have a WC above my FB with an opening between them and I can match temps or run them at completely different temps with no problems.

[Tospy]

Thanks guys....now I'm pretty convinced about adding a warming box.

My FB will be made out off an 1/4 inner shell and 1/8 sheet outer shell (insulated). Should I make the Warming box insulated as well? or Just make a separated box out off the 1/4 sheet metal. Is there a "guideline" in how big the opening between FB and warming box should be as well as for the opening between CC and Warming chamber? Can't find any relation between my fb/cc/ volume and the openings I!m talking about.

grtzzzz

[Dirtytires]

I used a 4 inch pipe for mine....same as the exhaust.

Just a mention, though 0.125 is definitely acceptable for the outer shell, you can definitely go thinner if you want. The goal is just to keep it thick enough as to not dent too easily. Steel is crazy expensive right now and only adds weight to your pit. The shell is only to hold the insulation so no need to get to beefy with it.

[Tospy]

Yep you've got a good point Dirty Tires...but.....the 3mm (0.125) sheets are here just to grab in my workshop (little bit a luxury situation) ....so a 4 inch pipe from fb to WC should be fine? damper on top of it etc... Is building an insulated warming chamber overkill or should I stick to 1/4 inch sheet and done?

[dacolson]

insulation between the FB and WC is recommended. It's pretty easy to keep it warm given the position over the FB so I'm not sure insulation would do much for you.

[Big T]

I insulated the top of the FB with 2'' Roxul, everything else on the FB/WC is just 1/4'' plate. I have a 5'' x 5" opening between them with a sliding damper on it, 4'' pipe would be plenty big enough.

[Dirtytires]

My firebox is insulated but I also chose to simply make the warmer cabinet out of 0.25 plate only.

[Tospy]

The idea behind the isolated warming box is to be able to use this setup as a vertical (insulated smoker). Just have to make some slider to close the opening between fb and cc in that case. Here in Belgium we have lots of types of weather and the ability to smoke reverse for low and slow and vertical for hot and fast could be an advantage i suppose. Beside using the chamber as a vertical smoker, i can use it as a warming bix as well ofcourse.

Think I'm going to stick to this idea......shoot me if I'm stupid

[Dirtytires]

Your pit....your money.....your time.

We only give ideas!!

[Tospy]

Hope to start the end of this week...first finishing this little one

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[dacolson]

That thing is sweet! What a great looking cooker. Is the whole thing insulated?

[Big T]

Neat looking cooker for sure!

[Tospy]

Thanks guys, this one had her maiden cook...absolutly awesome....from now on back on topic...

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[towtruck]

Mmmmmmmmm!

[dacolson]

Meat candy. Looks great