bigb Posted January 15, 2017 Share Posted January 15, 2017 How much of an opening do you find you need to keep it running smoothly? I am working on my doors and I know I'll never be able to close them all the way due to exhaust needs and I am planning to cut a small hole to act as exhaust relief and for viewing as well. I realize this can be quite variable but looking for a starting point. My forge has a 3/4" Z burner and is between 325 and 350 cubic inches. Would a 2 or 3 square inch opening be sufficient? I can start small and increase if necessary. My design uses hinges instead of sliders. It is nearly finished and I will post pics tomorrow. Quote Link to comment Share on other sites More sharing options...
WoodnMetalGuy Posted January 15, 2017 Share Posted January 15, 2017 I believe the rule of thumb is 7 times burner area needed for exhaust due to expansion of gases. So pi * r^2 * 7 = pi * 3/8^2 * 7 = 3 sq inches. A 2 inch square hole would be 4 square inches, and would be enough by that reckoning... -- Dave Quote Link to comment Share on other sites More sharing options...
Frosty Posted January 15, 2017 Share Posted January 15, 2017 Fire up the forge without a door and slowly close the opening till it starts effecting the burner performance and make the opening a little larger to account for work and drag around the work. An adjustable door is a good way to go. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
bigb Posted January 15, 2017 Author Share Posted January 15, 2017 Thanks for the good replies, Frosty I thought of that last night after I posted and that is exactly what I'll do, take the doors off and do some trial runs with stacked fire brick. I decided to give the hinged doors a try since I didn't want to be fumbling around with sliding bricks and stacking bricks. If this works I think it will be faster and easier. If it doesn't work then I'll get out the grinder and do something different. I did a lot of Googling and didn't find anything like this so I said why not give it a try? Quote Link to comment Share on other sites More sharing options...
bigb Posted January 16, 2017 Author Share Posted January 16, 2017 Some food for thought, in the Forges 101 sticky post #6 Mikey talks about a moveable barrier to allow exhaust gasses to rise out and up while the barrier, with it's reflective coating, reflects radiant heat back into the forge to help avoid a cold spot. I have an idea to cut only a very small viewing hole in the doors, then control the exhaust by leaving them ajar. I believe this will create what Mikey is talking about. What do you guys think? Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted January 17, 2017 Share Posted January 17, 2017 Yup. Of course you also need the viewing hole area to allow longer stock to stick through too. However, nothing prevents him from offsetting his doors a little bit away from the edge of the forge a bet to get the same effect as a movable wall of brick would give. Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted January 25, 2017 Share Posted January 25, 2017 "I believe the rule of thumb is 7 times burner area needed for exhaust due to expansion of gases. So pi * r^2 * 7 = pi * 3/8^2 * 7 = 3 sq inches. A 2 inch square hole would be 4 square inches, and would be enough by that reckoning... -- Dave " If any of us stop for a minute to contemplate what is glaringly obvious to anyone who used a burner or torch of any kind ever... the lack of PSI or orifice size of a gas jet shows these numbers to be irrelevant; since without them we don't have a clue about how fast, and therefore how much exhaust is being generated, do we!?! A mathematical formula not only needs to be right; it also needs to be completely and correctly applied to a given problem, or it is worse than useless. Quote Link to comment Share on other sites More sharing options...
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