Need help with a cold homemade propane forge


I am newish to smithing (1 year or so) and I took it upon myself to build a propane forge out of an old 20# propane tank. I lined it with 2" of kaowool, then satanite, then I realized that i needed more bulk to level the bottom and used some hard firebrick. Then more satanite to bind the firebrick together. Then i put down a layer of ITC-100. Then finally I used some bubble alumina to create a flux-resistant lining on the bottom. I have 2 homemade Ron Reil style forge burners pointed down from the top, with a needle valve each and a T-connector to a propane regulator that supplies up to 30 psi of propane. THe front opening to the forge is about 6"x3" and the back opening is 6"x2". I have tried to narrow that with firebrick to create more backpressure and keep in more heat to raise the forge temp to no avail.

My problem is that I can’t get it hot enough. I am nowhere near forge welding temp even with the forge running full tilt for a while. I have a few concerns but don’t know where to focus to get it hotter and was hoping for some help from this group to point me in the right direction:

  1. I read that using hard firebrick will absorb a lot of energy before it heats up. Could this contribute and do i need to dig that out and replace it with kaowool+satanite to fill in the bed?
  2. my forge burners aren’t performing super well I think. I get a lot of sputtering from one of them and my biggest concern is that they’re not loud enough when they’re running full tilt. I read that they should make it hard for someone to hear you speaking when near the forge - they don’t do that. I think that there is a problem with inducing air via the venturi effect and I don’t know how to tweak the design to fix that. I tried different tweco tip sizes (0.035, 0.030, 0.025) to vary the volume of propane to try to induce more air but it just makes the flame richer and burns through my propane super fast. My tips are fairly centered i think. I do wonder if the distance from the end of the tweco tip and the beginning of the burner tube is not right. The flare fitting i have at the end of each burner tube is a 3/4" to 1" reducer with the 1" threads burred off. It keeps the flame from blowing out but I wonder if the taper is too fast and that could affect the venturi effect and reduce the amount of air drawn in.

I’ll post some pictures soon on this thread but I would greatly appreciate some guidance from some of you pros. I could also bring the rig into DMS sometime.

-Brad Hershey


20 psi sounds way high: I run my two burner forge at 8psi. This is a issue for a couple of reasons:

  1. You need to abide by the Rule of Seven: don’t use the propane at a rate where you use up more than one seventh of the fuel per hour. Otherwise the tank will ice up and you’ll have problems with byproducts and sputtering.

3psi equates to about 1 lb/hr with two burners so at 20psi you’re dumping nearly 7lbs/hr. Unless you have a 50+ lb tank source, you’ll have issues. BBQ tanks are 20 lb tanks so you’d need three of them all connected and open. A 100 lb tank would be able to handle this volume ok, at least until it was well under half full.

  1. incomplete combustion. I suspect that you venturi air sources can’t support that burn rate.

My recommendation: turn DOWN the pressure and give the forge more time to heat up.

Other Possible Issues
Fuel mixing
If the fuel tips are too close to the top Venturi openings you can get burning at the TOP of the tube rather than the bottom where the fuel and air are well mixed.

Gunk in the fuel line could partially block the small tip opening: you can clean the tips with fine steel wire or a welding tip reamer. You might need to remove the tip and blow out the line with a compressor as well.

FWIW, my used forge had been sitting in a barn for a couple of years before I bought it and mud dauber wasps had nearly fillled one of the Venturi downtubes (and the regulator) with mud nests. I could clean out the downtube but had to replace the regulator.

Openings too big?
My Norco Forge has a 2x3 opening in the back (normally closed with a flapper door) and a perhaps 3x3 opening in the front when the front door is closed. Perhaps your openings are just too big. Try sealing off the back with firebrick completely and closing the front by 2/3 and see if that helps hold in the heat.


Thanks HankCowdog. Much appreciated. I plan to install a pressure gauge so I can ensure I’m not opening up the regulator too much. I’ll aim for 8psi.

I’ll check to see if I am getting any combustion in the mixing tube. I don’t think that’s the issue but I’ll check.

I will also close off some of the opening space to retain more heat.

My one open question is this: why aren’t my burners really loud when they are running full tilt? Could it be that I’m not inducing enough air flow? Could that be due to the inadequacy of the nozzles? I am using a 3/4-1” reducer with the threads ground out. Should I try to make longer nozzles with more subtle expansion? Could you recommend an easy to create/find option?

Also, I don’t have anything installed on the intake to the burners to restrict air inflow since I assumed that I was running rich anyway. Should I install a choke? I don’t have a lot of knowledge on how to tune the burner to ensure a neutral flame so any info you could provide would be appreciated. I have tried to educate myself on this at iforgeiron and other forums much to no avail.

Thanks again for your help.