250 First Time Texas Open Offset

[Texassmoke17]

Scored a 1946 250 gallon for my first build. Looking at doing a Moberg style with a round insulated firebox. Where is the best place to start to get an idea on firebox volume, also wanting to use a 8" 90 degree elbow reduced to 6" stack?

[Dirtytires]

Cool tank!

Start by plugging your tank volume into the pit calculator and it will tell you what your other volumes (firebox, chimney, vents, gap, throat) should be.

[Big T]

[Texassmoke17]

Took some basic measurements and looks like 87x 30 inch tank...

[hogaboomer]

Plug your numbers into this:

http://bbqpitcalculator.com/

[Dirtytires]

I'll make it even simpler than that....according to the North Texas Tank Company, the volume of that tank is exactly 246 gallons.

[hogaboomer]

I think he wants somebody to run the numbers for him.

[Dirtytires]

Yea, think you are right Hogaboomer. Got a few minutes this morning before I have to get back out to the shop so here is what I came up with.

Tank volume: 246 gal
Firebox size: 18942cubic inches is about right at 107%. Works out to 30" x 26" x 26"
Chimney: 1014 cubic inches. 8" x 20" would look pretty good
Intake: 60 square inches total. I like one on each side of firebox so 30 square inches each.
Throat: 162.25 square inches.

Another thought is to check out the plans that Frank has on the home page. If you look on the home page, he has a free set of plans for the "legacy 250" which would give you a ton of information and great reference for your build. It will cost you $12.95 for shipping and worth every cent in my opinion. Of course, we are here to help if you need it as well.

Hope this helps....

[Texassmoke17]

Mainly just double checking myself on firebox throat opening and stack size and length... I maybe over thinking alot of it...lol, wanting to do a round fire chamber with square insulated box. 24x30 was my calculation for chamber size but was gonna mount it more like a square is mounted....

[Texassmoke17]

Was looking at going with an 8" round elbow and reducing it to 6" pipe stack

[Texassmoke17]

Finally getting started on build. Old tank has fairly short end caps approximately 8" to weld seam. Will that be deep enough to mount firebox or should i cut it deeper?

[Dirtytires]

Should be just fine. Congrats on the start!

[Texassmoke17]

Have about settled on 26x26x28 fully insulated fire box... Calculator shows to be 99.93%... Will that work?

[Big T]

That should be fine, especially with it being insulated.

[Frank_Cox]

Looking great!


Sent from my iPhone using Tapatalk

[RMB BBQ]

Subscribed! I'm in the middle of a 250 and 100 build.....well the beginning not middle. Very interested on your progress. Keep it up. I know it's hard to build these things with a 40+ hour work week and a honey do list.

[Texassmoke17]

Yes, defiantly gonna be a slow build... Another question, with doing a fully insulated firebox should I raise the box to put the throat opening exactly at grate level?

[Dirtytires]

Insulated vs non- insulated does not alter the throat size or height.

[Texassmoke17]

Due to the double wall thickness of the insulated firebox that would put the top of throat opening 2" lower than the grate?

[Big T]

A lot of builders raise or lower the throat location on an offset depending on how the want the air to flow.

[Brewmaster]

Due to the double wall thickness of the insulated firebox that would put the top of throat opening 2" lower than the grate?

Pit builders like Jambo have the throat opening at grate level, others a couple inches or so below. For me, grate level is preferred a bit, it helps keep the hotspot on the grate smaller/closer to the inlet, and sort of emphasizes top-down cooking.

Pic of a Jambo for a visual, they look like the firebox is way too high but they work great.

[Texassmoke17]

Got a little bit further.... Doors stayed pretty straight.. How muck warp is ok? Mine are maybe 16th to 8th in some spots.....

[Dirtytires]

Acceptable door warp is dependent on how picky you are and the size gasket you are using...lol.

A typical gasket will crush about 50% so if you have a max gap of 0.125" then you would need a gasket thickness of 0.250" to seal properly. This is a very common size gasket and a reasonable gap if you are happy with it. My guess is you could pull the gap back to 0.0625" and use a smaller gasket but only you can decide if the extra work is worth it.

One thing I will mention is that you do not have the flanges on your door yet so gap is pretty hard to determine at this point. It is common for the flange to alter the gap depending on welding heat, the metal memory of the flange and the smoothness of the bend.it might be of benefit to finish your door before deciding to bend it any.

Last point I notice is you appear to have welded your hinges on already. Unless you have already decided on a gasket thickness and shimmed the doors accordingly before installing them, you have a good chance of having a problem with the doors binding. If this is the case, you should aim for the thinnest gasket possible to avoid binding or plan on cutting off your hinges and re-mounting once the door is complete. And don't feel bad, a large percentage of new builders forget this step!

[Texassmoke17]

Didn't think to adjust for a gasket...Hinges are just tacked for now, so may have saved a little bit of trouble... What are some go to gaskets to use?

[Dirtytires]

Lava rock makes a really good peel-and-stick tape style gasket. As long as you clean the metal properly and let it cure properly, it will last a long time and has absolutely no mess like the glue applications. I've had mine on for 6 years now and no problems.