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[newmod]

Hello,
    I am new to this site.  Looks like great site.  I am planning on building a OWB.  What wall thickness steel should be used for the firebox.  I used to own a Central Boiler, so I am familiar with OWB, just not with building them.  I have seen some others on here use a propane tank cut in half.  Looking to go that route, but will it hold up as a firebox.  Thanks all>
Newmod

[BoilerHouse]

There is a lot of heat stress in this area.  A thin firebox wil give better heat transfer but may not stand up well over time.  My firebox is 3/8 inch.  It should be around for a while.

[Airgap]

Mine's 1/4", I wouldn't go any thinner on a fire box....

[newmod]

Airgap,
     I just finished looking at your pic from your OWB that you made.  Very impressive.  I have been contemplating a round or square firebox.  How long did it take you to make yours.
Newmod

[Airgap]

Thanks. Mine's pretty simple compared to some that have been built by people on here.

Anything round will be less welds, which saves time and is less work, and if you are not a good welder, it will reduce the chances for leaks.

I probably have around 80 hours in mine spread out over a couple of months. Give or take.

It's not something for a novice fabricator, but if you have the skills it will be very enjoyable.

[rosewood]

 3/4'' thick on mine, propane tanks are pretty thick.good choice ..what happened to CB furnace.

[Scott7m]

3/4 inch thick, are you serious? 

I know of a lot of furnaces around over 20 years old, some have mild steel 1/4" boxes and
others have 16ga sooo, go figure! 

I'm really not sure the actual metal thickness is important as the quality or the person welding it. 

My cousins fire box is 1/16 of an inch an this makes it's 23rd season

[willieG]

i think 1/4 or better is good the pipe i used is 7/16  and that is the way it came from the junk yard and i think a lot of propane tanks are about 3/8

[rosewood]

o yea im serious,3x5 firebox,1''end plate 5/16 thick chimney,1700lbs just in firebox steel. hold heat for alooong time

[yoderheating]

 Wow, you are losing a lot of heat using a firebox that thick.

[newmod]

Rosewood,
     The CB i had went with the house that I sold.  THAT WAS A MISTAKE, SHOULD HAVE KEPT IT, (the OWB ).  I have no problem with the fabrication part.  I just found a good price in 1/4 in  x 4' x 8' steel plate.  So i will be making a road trip soon.  I really like the simplicity of the way AIRGAP constructed his.  I have an indoor WB and hate the mess, smoke etc.  BACK TO OUTSIDE !

AIRGAP,
     Did you put a baffle ? or whatever it is called to keep some heat in the firebox, so it all doesn't go out the chimney.

[jackel440]

I would recommend you go with the 1/4" plate.3/8" at the Max do to the heat transfer rateno point in spending extra money on steel when its not really doing you any good.use the money for other important parts.as long as you maintain the inside in the off season it should last for many seasons.

[Airgap]

Rosewood,
     The CB i had went with the house that I sold.  THAT WAS A MISTAKE, SHOULD HAVE KEPT IT, (the OWB ).  I have no problem with the fabrication part.  I just found a good price in 1/4 in  x 4' x 8' steel plate.  So i will be making a road trip soon.  I really like the simplicity of the way AIRGAP constructed his.  I have an indoor WB and hate the mess, smoke etc.  BACK TO OUTSIDE !

AIRGAP,
     Did you put a baffle ? or whatever it is called to keep some heat in the firebox, so it all doesn't go out the chimney.

No, I didn't put a baffle in mine. My flue travels about 18" horizontal through the water and out the back. This gives me more surface to heat water. I don't know if It'd be better with a baffle or not. It's doesn't get very hot where it comes through the jacket on the back. It would be fairly easy to go back and weld one in.

[rosewood]

yoder, why would i be losing a lot of heat? have you ever heated steel before?  what cools faster thicker or thinner steel?

[jackel440]

yoder, why would i be losing a lot of heat? have you ever heated steel before?  what cools faster thicker or thinner steel?

Rosewood,The btu's needed to heat your thick firebox could already be heating water if it weren't for the extra steel.I think your steel holding the heat longer is not worth the lost burned wood.When I am fabbing with 1" material with a rosebud the steel still cools fairly quickly,and if it surrounded by water your still cooling it quickly.You might hold heat a short time longer than a thinner box.You know it takes alot of heat to get a 1" piece of colled roll up to a required temp than a thinner guage.But poor cold water on it and it cools off quite fast.A thinner box is already transfering heat to the water while the thicker box is still trying to heat soak.
Same reason you don't weld aluminum lying directly on a steel work bench.The thick table will suck the heat right out of your work piece before you can even think about welding it.Wasted time and material to heat the piece.
Just my thinking on the subject ,and no boilers were hurt in this crazy explanation.   LOL!