Chimney on a forge?

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by DevinT, May 9, 2016.

  1. DevinT


    Jan 29, 2010
    Anybody have any experience putting a chimney on a forge?

    I just built a 27 inch forge, because of it's size, it has 4 burners. It is throwing a two foot flame out of the door. Just wondering if I could put a chimney on it to redirect the flame up and out.

    I remember Robb Gunter designed a forge with a heat exchange/chimney twenty years ago.

  2. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    I have a forge partly built pretty much like what you have. It is a five burner 30" long. It has a 4" round vertical chimney at the rear port.

    I have seen a chimney used on several vertical forges, and on industrial forges. Basically, it is just another port ... usually it is over the rear port. This is a situation tat putting the burners in facing toward the rear will really help.

    Be aware that the chimney will get red hot. It needs to be either a double wall with wool between them or even better, have a wool and refractory liner. I haven't experimented with it yet, but I have several lengths of stainless tri-wall fire place chimney which may be just the trick. It should work perfect by dropping it over the existing 4" forge chimney pipe.

    Notes and Caveats:
    If the shop has lots of room behind the forge, merely facing the burners toward the rear might solve the dragon'd breath problem. This can be as simple as turning the forge around and using the existing rear port. You might want to make a portable "BLAST ZONE" sign, like uses around jets, to place behind the forge so no one gets singed.

    If using a chimney, you have to consider the vertical impact zone of lots of hot gasses and flame. Make sure there is enough overhead space above the forge not to set the roof on fire.
  3. Atlas Knife Company

    Atlas Knife Company KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Feb 16, 2010
    4 burners, straight in or swirling?
  4. DevinT


    Jan 29, 2010
    Swirling, do build a large forge?

  5. javand


    Oct 17, 2010
    Most large gas pottery kilns have them. I've taken a lot of my forge building stroke lately from a friend of mine who teaches, and builds large salt and normal pottery kilns for a couple of universities. Many in the multi-million BTU range.

    There'll likely be some tuning caveats, and you'll probably want a damper on the flue, otherwise you may develop too large a draw, and suck oxygen into the forge door, creating atmospheric problems and uneven heat. I'm sure it'll require some careful tuning, since we're unlikely to follow the route of the pro's which would calculate the size of the chimney and height relative to the furnace and input, etc.

    I'm looking at going this route with my large ribbon burner forges (which you should look into btw) also, as the heat output is just too high to be tenable anymore. Even with really heavy roof ventilation, it's in the 120's in here by the end of my forging sessions, and takes hours with the bay doors open at both ends to cool back down. Nice in the winter, but sucks currently.
  6. deker


    Nov 14, 2005
    Are the burners forced air or atmospheric? You might be able to reduce the insane dragon's breath a bit if they are blow burners by turning down the gas input a bit so that you're not throwing so much unspent fuel out the door.
  7. DevinT


    Jan 29, 2010
    We tried both, no difference.

  8. A C Richards

    A C Richards

    Apr 14, 2006
    Reduce the size of the orifice. I have been able to drop the amount of dragons breath to a great extent. I have gone as small as .017 but that was for my salt pot. Controls the temp really well. On my welding forge I have been running .032 but I get a bit of the breath. When I turn off the front burner it drops significantly. It does reduce the temp into the 2200 ranges though. I normally run 2350f or so welding. I have had it up as high as 2500f. But that was just a waste of gas. This is on a 2 burner 22" forge 6" ID.
  9. A C Richards

    A C Richards

    Apr 14, 2006
    I guess I should add I run a .026 I think on my general forging tube. I have not put a thermometer into it yet but I know it can weld, I did it Friday.

    Have not run a chimney but I thought about making a heat exchanger to capture some of the exhaust heat. It might make things a but more efficient. Just have to keep it under 900f.

Share This Page