Firebox Dimensions and welding tips

The firebox total size is 24" wide by 24" deep and 28" tall.  However it also has a chimney area attached to that back that is 10"x6".

The door boxes extrude out 12 inches, and are 6"x24" (for the lower one) and the top one is 16"x24".  This gives room to build the shed around the door, and be able to put in insulation.

All steel in the firebox and chimney is 1/4" steel.

Isometric view of firebox plans for wood boiler

Inside the firebox, you will also need to weld in the v-bottom plates, and plumb the primary and secondary air.  The primary air will go in the front between the two doors, and the secondary will need to be plumbed into the back about 2" from the bottom.

Here is a video to see how this works when it is setup.


Welding tips:

When welding the boiler (and especially the firebox), I found it best to fit the bieces together like this:


I did all my welding with a cheap harbor freight welder, and was able to get great welds that are water tight welding like this.  I also did a bead on the inside as well.

6 comments on “Firebox Dimensions and welding tips
  1. Richard Penuell says:

    I am build a outdoor woodboiler, need suggestions on how to build door.

    I am using 3 foot by 6 foot water tank with a 23 Inch skidder wheel as fire box and 6 inch pipe as smoke stack…Have not figured out door, would you offer suggestions….richard

    • David says:

      Hi Richard.  The door is probably the most complicated part of the boiler (not hard, but has a lot too it).  I built mine out of angle iron, and flat steel, making a box with a slot around the outside for fiberglass rope to fit in.  The main part of the door is about 2 inches thick filled with ceramic insulation to keep the heat in.  I have had a lot of question on specifics like this, and it is very hard to explain without pictures.  For this reason I drew up some plans, however because of the time it took me to do this, I do have to charge for them.

      Thanks for visiting my site, and good luck with your boiler.

  2. Shane says:

    A++ for your effort. Its looking awesome!!! Would love to hear your toughts when winter is over. But in the meantime, can you put the dimensions on the drawing? I added the dimension above and i'm not getting 28". Now that you've been burning for a few months now, would you make the fire box or secondary area bigger ( taller, wider, deeper)? Could you post some photos, i'm getting vertigo.

    • David says:


      So far, I have noticed that I would like the firebox a little bigger (taller).  Mainly because I didn't plan on wrapping it with firbricks (but the firebricks help keep the heat up and make a cleaner burn).  However after wrapping the entire thing with firebricks, it made it a little too small.  I can still get a good 12 hours between fills, but If I made it a little bigger I could get 24 hours.

      I will work on getting some drawings with dimensions, however I dont' really have any good pictures of the firebox, but I will add what I have.

  3. Jake says:

    How big is the plumbing for your primary and secondary air feeds and do you use a blower to supply the air to the secondary burn or just let it vacuum feed?

    • David says:

      I am running 2″ lines to both the primary and secondary (except the internal plumbing for the secondary is only 1 1/2″.  I have my one blower that feeds both the primary and secondary with ball valves where I can adjust how much air goes to each.  If you have seen all my youtub videos, you will see that I did only use an open vent for the primary at one point (when I was using a cyclone mixer).  This did work very well, but I had to remove the mixer to add more room in the primary chamber to maintain a 12 hour fill time.  What I am using now works just as well, is simpler, and uses less room in my primary chamber.  But it does require forced air into both the primary and secondary.

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