a62rambler Posted April 12, 2012 Share Posted April 12, 2012 I know that a 12" round pipe or a 10" square pipe is what I need. If I put two 6" round would it work as well as a single 12"? That would be easier for me to do since 6" and 8" pipe is available locally but 12" non galvanized would have to be ordered. Quote Link to comment Share on other sites More sharing options...
pkrankow Posted April 12, 2012 Share Posted April 12, 2012 You can join two 6 inch sections at the seam and get 12 inch diameter. Circumference increases at the same rate as diameter. However 2 separate 6 inch pipes are only 1/2 the area of a 12 inch pipe. It is the squared bit that causes this. When you double diameter you quadruple area. The concept applies to square pipes too. If you have a square pipe with unit 1 sides, and put two next to each other you get a rectangle that has 2 units square inside, and a common double wall. If you take the side lengths and add them up, then you get 4 sides 2 units long with a contained area of 4 units square. When you make it a circle and throw pi in it gets confusing for no good reason for some people. Hope this helps. Phil Quote Link to comment Share on other sites More sharing options...
Pat Roy Posted April 12, 2012 Share Posted April 12, 2012 The simple answer to your question is no. Order what you need. Quote Link to comment Share on other sites More sharing options...
a62rambler Posted April 13, 2012 Author Share Posted April 13, 2012 Thanks Phil! I should have thought of that. Quote Link to comment Share on other sites More sharing options...
Trip Posted April 13, 2012 Share Posted April 13, 2012 I use galvanized 12" vent pipe and it works fine, with the pipe being 3 feet above the fire, I don't worry about any fumes from the galvanization. If there is any fumes, it goes right up the flue. Quote Link to comment Share on other sites More sharing options...
Pat Roy Posted April 29, 2012 Share Posted April 29, 2012 Trip, is your pipe galvanized on the outside too? It might be far enough away from the heat not to be a problem, but take the risk? Quote Link to comment Share on other sites More sharing options...
a62rambler Posted April 30, 2012 Author Share Posted April 30, 2012 I'll pass on galvanized. Besides mine will sit right next to the fire so I'll stick with my cobbled together washer metal and use two pieces of stove pipe like Phil pointed out. I did manage to get the rest of the forge going and fired it up with some wood to test the blower and it all works. It sure isn't going to win any beauty or engineering contests but it works. Quote Link to comment Share on other sites More sharing options...
Backwoods Blacksmith Posted April 30, 2012 Share Posted April 30, 2012 If you use galvanized ducting and it burns off, it will only do it once. There is not a continueing problem. Plus the metal needs to be in the red hot range before it cooks off. I have never seen a coal forge flue get that hot. So what is the problem? I used corrucated galvinized tin 36in by 8ft to make mine. Rolled it into a circle and used sheet metal screws to fasten the overlap joint. The flue opening and hood are 10 gauge and painted with high temp paint. Plus I got it as salvage. Use the galvanized and don't worry about burnoff. Quote Link to comment Share on other sites More sharing options...
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