Building a firebox for hot smoking

el Ducko · Post by **el Ducko** » Wed Mar 21, 2012 20:40

You know the problem- - you buy a smoker, build a fire in the firebox and hot-smoke a brisket or twenty, it does great on the first nineteen... Then the firebox bottom rots out, and you have to either junk the thing or replace the firebox.

The "big boys" weld up great looking heavy wall fireboxes. Some folks weld up 55 gallon drums into smokers. Me...? I once rented an oxyacetylene rig, went through a full cylinder of oxygen and five drums, and got about one and a half working smokers. ...which looked amateurish, and rotted out a year later.

I bought a new firebox for my horizontal Brinkmann at Lowe's. It was a different brand. Now I have to load the firebox from the wrong side. ...plus, it's gonna rot out, just like the others did.

...and so will the one on the vertical smoker.

What can you imaginative folks out there in hot-smoker land recommend for either building or getting built a decent firebox? (Please answer the poll above, then add on a reply or suggest a better option, if you care to.)

ssorllih · Post by **ssorllih** » Wed Mar 21, 2012 21:19

Ducky, You could build a new fire box with fire brick and furnace cement. A diamond saw blade for a skil saw will cost about 25-35 dollars and will cut a few thousand bricks. A well fitted brick will serve for a loading door and possibly as a draft control. Even the steel combustion chambers burn out early. Cast iron and firebrick are the only materials that will stand fires for long periods.

Post by **Butterbean** » Wed Mar 21, 2012 22:53

Personally, I'd love to make one out of brick but I don't know squat about laying brick but I do know how to weld and I have plenty of scrap metal and a good cheap source for tanks so I'd go that way.

A very easy build and it turns out to be a very nice smoke is to stand a lp tank vertically and cut out a door in it. To the side of this you pipe the smoke in from a stand alone fire box that is made from 3/8's inch plate. Very little welding, very little cutting and it does a great job. If the firebox ever rots out, you just replace the bottom by welding another sheet on top of that one.

sstory · Post by **sstory** » Wed Mar 21, 2012 22:54

To prevent rusting out the bottom of the firebox, make sure to remove the ashes after every cook (after the ashes cool of course). When wood burns, it creates moisture. Moisture and steel are a good combination for rust.

Also, make sure the wood is not sitting on the bottom of the firebox -- there should be some airflow under the burning wood. You can use a grate out of a fireplace for this or get a piece of expanded metal and use stainless bolts and nuts to make "legs" to keep the grate up off the bottom of the firebox.

Sorry, I didn't catch where you are from, but you might check ebay or Craigs List to find a used smoker that somebody has built. Normally, these smokers are built out of thicker steel than the smokers you can get at any of the big-box stores. Find one with 1/4" steel for the firebox and as long as you clean it out, it should last a long time.

ssorllih · Post by **ssorllih** » Wed Mar 21, 2012 23:06

When we were kids we all played with blocks and built wonderful structures. Firebricks are just big boy blocks and furnace cement is just glue. You aren't bricking a house just building a little brick cylinder. Cut the bricks into segments and glue them together after you have dry fitted them. Lay one segment on two so that the joints are staggered.

el Ducko · Post by **el Ducko** » Thu Mar 22, 2012 02:49

Do you think there's any advantage to building with firebrick versus steel? I'll have to give up portability either way, looks like (but who cares?). I realize that I'll never be able to weld a bead like the maintenance guys back in the chemical plant did, but it sure would be nice to have a steel firebox.

What sort of pros and cons are there? ...would appreciate your input.

*** Firebrick-only advantages:
...Easy to build.

*** Steel advantages:
...Can be as air-tight as needed.
...many configurations possible.

*** Firebrick-lined Steel advantages:
...Steel advantages, plus...
...long lasting
...little to no paint heat damage

ssorllih · Post by **ssorllih** » Thu Mar 22, 2012 03:30

The firebrick combustion chamber can be built air tight. The steel combustion chamber can be built air tight. The firebrick chamber can be broken with a hammer, the steel chamber can be dented with a hammer. The firebrick chamber won't burnout, the steel chamber can burn out. Firebrick lined steel won't burnout and doesn't need to be heavy gage steel. You could use a steel five gallon bucket. Firebrick lined steel has the advantage of a fire proof lining and a non friable exterior. Should have a drain hole in the bottom. The firebrick doesn't have to be four inches thick. You can buy firebrick at about one inch thick. You can saw it into segments to make a smooth liner in a steel cylinder. One gallon of furnace cement costs 12 dollars at home depot. Spread it with a flat stick.
The outside of a lined steel combustion chamber will be much cooler than an all steel chamber.

Oxide · Post by **Oxide** » Thu Mar 22, 2012 15:40

Butterbean wrote:
A very easy build and it turns out to be a very nice smoke is to stand a lp tank vertically and cut out a door in it.

How do you vent the tank to be sure all propane is out of it before cutting into the tank? My though was to fill it up with water then drain it, then cut.

Oxide · Post by **Oxide** » Thu Mar 22, 2012 15:43

sstory wrote:
To prevent rusting out the bottom of the firebox, make sure to remove the ashes after every cook (after the ashes cool of course). When wood burns, it creates moisture. Moisture and steel are a good combination for rust.

Excellent suggestion. I remember reading something about ashes rotting through steel when wet and that is what takes out more Webers than anything else -- folks leaving the ash in the bottom. Apparently, when dry the ash isn't a problem.

ssorllih · Post by **ssorllih** » Thu Mar 22, 2012 16:47

Remember wood ashes were the source of alkali for soap making before sodium hydroxide became commercially available. Dry wood ash can't react with anything but adding water turns it into a chemical soup that will stain wood, clean cooking fat from pots, pans and dishes. Nice clean wood ash can be used a leaven for biscuits and pancakes.

Oxide, remove all of the threaded fittings and purge the tank with CO2 or nitrogen or water or just a large volume of compressed air. The limits of flammability are 8% at the lower end.

Oxide · Post by **Oxide** » Thu Mar 22, 2012 17:09

ssorllih wrote:
Oxide, remove all of the threaded fittings and purge the tank with CO2 or nitrogen or water or just a large volume of compressed air. The limits of flammability are 8% at the lower end.

Thank you, sir!

el Ducko · Post by **el Ducko** » Thu Mar 22, 2012 17:11

Good information, folks. Thanks.

I remember trying to silver silver solder a leaky VW gasoline tank which had been washed and purged. There was residual stuff in there, though. The tank suddenly tried to become spherical. (I was very lucky.) Propane tanks are not subject to such problems, but do take care. I'd wash, then purge, maybe even put a nitrogen purge on it.

Do you think using firebrick inside steel is overkill? I think the reason most people use (or buy) steel is because it's portable. No need for that, here.

Looks like my main worry would be solved by putting a metal tray with a grate on it inside the firebox, then emptying it after each use.

Any hints on connecting the firebox to the smoke box? From Ross's earlier pictures, it looks like stovepipe fittings work well. For hot smoking, I'll need the insulated version, right?

Is this sort of thing covered in Stan & Adam's smokehouse book? I've been too cheap to buy it, up until now, but I hear a little voice chanting "Amazon! Amazon!" and it ain't referring to a women's army.

ssorllih · Post by **ssorllih** » Thu Mar 22, 2012 17:32

If the smoke pipe run is vertical you can use any non combustable pipe. If the run is other than vertical, the pipe will have to be metal or supported clay flue liner. The insulation can be found in plumbing ahd heating supply shops. But insulation has to be kept dry.

el Ducko · Post by **el Ducko** » Thu Mar 22, 2012 17:53

Ross,

I'm thinking about the double-walled type of stove pipe used for heating purposes on gas-burning or wood-burning free-standing stoves. I don't have any experience with that sort of pipe, but believe that there's a kind with an air gap and a kind with insulation between layers of metal.

Have you used that type in your several smoker "inventions"? ...had any rust problems after they get hot a few times, sit outdoors for a couple of years, etc.?

Russ

ssorllih · Post by **ssorllih** » Thu Mar 22, 2012 18:20

Russ , the smoke pipe that I have used is just steel down spout that was laying under the shed. The double or triple wall pipe you mention is used, exposed, for both inside and outside installations.