How to insulate a fire box

[Frank_Cox]

Howdy everybody!
I wanted to start off the next few days with a thread about
How to insulate your firebox and build subframe doors.

This will be day 1.

I'll post a new pic in this thread everyday over the next few days showing my process.
Hope this is found to be useful!

This post shows the outer box for the firebox and warmer which I build as one piece. This is where I start the build.

To get started,
First use our free calculator found at bbqpitcalculator.com
OR a set of smoker plans from smokerplans.net
to get your firebox dimensions.

Once you have your firebox dimensions, use them for the inside dimension of your firebox.

Then add your insulation thickness to those numbers for each side of the box you plan to insulate.

Next do the math for the dimensions of your outer box.

In this case I used the 1.5 inch roxul from our website smokerbuildermfg.com so I added 3 inches to the width of the box and 1.5 inches to the depth.

If you plan to insulate the door be sure to add that in as well.
In tomorrow's post we will start adding insulation.

Then build you outside box first.

Hope this helps someone!!!

#smokerbuilder #smokerbuildermfg #smokerbuilderforums

[Frank_Cox]

Day2: How to insulate your firebox and build subframe door trim.
Today the background pic is shown with the firebox and warmer in the vertical position. The throat has been cut and is a trapezoid shape.
I started with a chunk of insulation cut to the width of the firebox then the height is the number from our FREE pit calculator found at:
bbqpitcalculator.com
After insulation is cut to the required size I install the chunk of strap for the bottom of the throat. This is shown in the Throat detail pic.
In this case my insulation is 1.5 inches thick so I used 1.5 by 1/4 inch strap. This will be used to tack the inner plate during the next step in assembly.
Let me know your thoughts and questions by replying to this post!
Hope this helps you!!

Couple more resources you might find useful:
Smokerplans.net has plans for your build!
SmokerBuildermfg.com has all the parts and kits!

[Frank_Cox]

Day 3: How to insulate your firebox and build subframe door trim.
On today's post we are putting in the back plate. I like to get a wrap around corner for the insulation. This way there is no side contact between the inside skin and the outside plate.
Notice how the bottom trim strap we installed yesterday gives us a place to tack the top of the inner back plate in place and we also tack the plate on the bottom.
I make the width of the back plate short the thickness of the insulation for the side walls.
That was an easy one haha!
So tomorrow we will look at the side walls!
Hope this helps you!

Couple more resources you might find useful:
Smokerplans.net has plans for your build!
SmokerBuildermfg.com has all the parts and kits!

[Frank_Cox]

Day 4: How to insulate your firebox and build subframe door trim.
On today's post we are talking about adding the insulation and the panels for the left and right sides of the inner firebox.
If you remember yesterday's post we installed the back wall.
we made the plate a little shy of the side walls by 1.5 inches each side which is the thickness of the insulation I am using.
So image 1 shows placing the insulation in place.
The insulation will be the same height as the back wall.
Image 2 shows installing the left side plate.
It is important to point out the inner plate is 1.5 inches short from the opening of the firebox. This is going to allow for the subframe door.
Image 3 shows how the insulation wraps the corner so to speak.
We want to make sure there is a s tight as possible fit. Also note how the inner plate is tacked in the back corner.
Image 4 shows how we repeated the process on the right side of the firebox.

That's it for today! If you have any questions comment them!
I hope this is helpful!

[Frank_Cox]

Day 5: How to insulate your firebox and build subframe door trim.
On today's post we are installing the top cap of the firebox, the insulation above it, and the bottom plate of the warming cabinet.
On pic 1 I made the firebox plate cap a little shorter than the full width of the inside of the cabinet so I could prevent full contact and keep the insulation barrier full wrap around the top of the firebox.
Pic 2 shows cutting and fitting the insulation in place.
The part I didn't think to get a pic of is where I cut the hol in the warming cabinet plate for the damper. I used a chunk of 4 inch schedule 40 pipe so I cut the hole 4.5 inches. Then I removed the insulation and placed the bottom warmer plate directly on top of the firebox cap and traced the hole so they would be perfectly lined up.
I cut both the holes and reinstalled the insulation.
Pic3 shows the bottom warmer plate installed and the insulation in place.
Pic 4 shows the reveal of the bottom warmer plate. This is important because of the way we will trim out the subframe door.
Some more notes. The inner firebox plates need to be kept short 1/4 inch the thickness of your angle for the subframe. I am using 1.5 inch angle so my plates are 1.25 inches short. The bottom warmer plate should be a good fit to the insides of your cabinet to be seal welded. the door side of the warmer plate should be flush with the outside of your cabinet.
One more thing. Tack everything where you can cut a weld to bring things into square. Don't weld it solid yet.
Hope this is found to be helpful!

Comment your questions! I'm glad to answer them!

[Dirtytires]

Great post Frank....glad to have you back!

[Frank_Cox]

Great post Frank....glad to have you back!

Hey bro! Glad to be back! It has been an interesting bit of time... Long time...
It's been hard to participate and also run the business.
Have been fortunate to be able to add some really great team members which should make it easier to participate in some of the action on here!
Always know I am watching and reading along but it may be difficult sometimes to participate in real time.
I really appreciate you all more than you know and this will always be my favorite place on the internet

[tinspark]

this will always be my favorite place on the internet

I am kinda feeling the same way about this place. I belong to a few other forums (CNC plasma cutter type stuff) and really enjoy spending a bit on them to unwind, but I am finding myself here first.
I think it may be fabrication and food combo?? I get some good ideas here and steered in the right direction too... Appreciate all of the many years of experience shared here..Also, some of my buddies have been wanting them to help build some stuff for them too. I don't like charging friends, so I often take a loss on stuff. and rarely break even. But things come my way too
Great details on the pics and description. VERY EASY to understand.

[Frank_Cox]

Thanks for that tinspark and glad to have you here!!

So Here's day 6!

Day 6: How to insulate your firebox and build subframe door trim.
On todays post we are installing the subframe door trim.
The biggest thing to keep in mind when making subframe doors is be sure to tack everything. Don't weld solid until the end so you can make sure everything is square and true. A long straight edge comes in handy for this. I use a 6 foot rule.
Pic 1 shows that I prefer to cope the corners. sounds time consuming but it is actually perty fast. I use a metabo with a slicer disc. Start your framing by cutting all of the horizontal pieces first. then begin at the bottom of the cabinet and work up. Use some number 11 clamps to hold parts in place.
Pic 2 shows the reveal I leave so I have a good place to weld all the way around the outside of the frame. This way you can grind and polish if you like.
Pic 3 shows 2 things. First off how I cope the vertical angles. second it shows the bottom warmer plate sandwiched in between the 2 horizontal angles leaving a reveal to weld in. Sometimes this will need 2 passes to get a nice bead.
Pic 4 shows the entire assembly put together and ready to weld. On the firebox sides and top notice that one leg of the angle caps off the end of the insulation. I also leave a 1/4 inch reveal there as well for a nice spot to weld.
Once you get it all installed and tacked together, I recommend laying the cabinet on it's back and making everything level. Then check for square before welding. I have had best results welding in a skip and hop pattern. In other words I don't make one solid pass. Things tend to move or bow with that much welding at once. Just make sure to wire brush your restarts and do a good tie in and you will be fine.
For the door, just make an angle frame of the next size smaller angle and lay your door panel in it. The magic number here is 3/16. You want to have as close to 3/16 of an inch gap as possible on all sides of your door to the edge of the frame. This will give enough clearance.
Hope this helps!!

Couple more resources you might find useful:
Smokerplans.net has plans for your build!
SmokerBuildermfg.com has all the parts and kits!

[EverydayDiesel]

Is there no insulation at the bottom or top of the firebox?

[Big T]

Is there no insulation at the bottom or top of the firebox?

There's insulation everywhere but the bottom of the FB, you can see the insulation in the 4 pictures that are together. He's building a WC above the FB so he doesn't have it sandwiched in yet. The bottom of the FB doesn't get very hot so there's minimal heat loss there.

[WatchDog]

Hi, I was wondering if granulated vermiculite could be used instead of kaowool or the fibrous insulation?

[Dirtytires]

Never had anyone ask that and really don't know. With so many high-temp ceramic and fiber insulations on the market I'm not sure I would try it. It just seems messy when compared to roll insulation.

[towtruck]

I used vermiculite to insulate my pizza oven. I used a cement binder just to stick it all together to my brickwork. It will transfer heat but it does it slowly. I think loose crumbs will do the same thing as the air in the mix will allow heat transfer. There is one way to check it though.....build a small double walled test plate and fill it with crumbs and heat one side....check to see how it transfers heat to the other side. A simple square of steel the thickness of your fire box and some aluminum foil to make a pouch for the vermiculite and set it over a heat source......I love experiments!