nathand Posted September 9, 2013 Share Posted September 9, 2013 Hello everyone I’ve finally managed to complete building my own forge and have got it up to some serious heat however i am now at the next minor issue and that is the hot air extraction?? First of all let me explain my situation i have only one real place where i can use the forge and that is at my mother’s house where i built a small workshop some years ago, now the walls are concrete block with a concrete floor, however the roof is timber and bitumen. Now when i started building the forge i did not want to cut a hole in the roof as was worried the heat transfer might catch the roof on fire, i wanted to vent the forge by using the same type of fan i used to blow air into the forge, this is a 750 watt chip/dust extractor i have an electric fan control device which i can vary the speed of air into the forge but was planning on having no such device on the extractor fan now this weekend i put in place all my metal spiral ducting and mounted the extractor fan to the ceiling. i managed to get the forge nice and hot but there were some issues the shed was still very Smokey, as i used some timber to get it going, and within about 5 minutes i had to shut everything down the extractor fan motor had become very very hot so much so i thought that any moment the windings were about to catch fire i think the problem being that the motor is very close to the fan body itself and the hot air has transferred heat into the motor so now i am not sure what to do???? Is it best to install a chimney??? im still worried about the heat transfer?? or do i adjust the extractor fan so the motor becomes remote and operates on a pulley belt system??? What have you guys done?? I have an attached picture of the forge unfortunately i have no piccies of the fans or extraction system i will try and get these in a few moments Quote Link to comment Share on other sites More sharing options...
Chestnut Forge Posted September 9, 2013 Share Posted September 9, 2013 Is the extraction mounted in the flow of the smoke? I'm using charcoal in my forge and don't have a hood over it yet. The little bit of smoke that it makes just gets sucked out by an exhaust fan mounted at the peak of my garage roof. I do keep a fire extinguisher two step away, though. The only problem that I have is the ash, it is heavy enough that not all of it gets pulled out. If I understand this, you are using something like a shop-vac motor/blower? Quote Link to comment Share on other sites More sharing options...
Marksnagel Posted September 9, 2013 Share Posted September 9, 2013 Hi Nathan, First let me say welcome to IFI. Second let me ask you where you are located. There may be other smiths in your area that could visit your shop and give you some good pointers. without more pictures it's hard to tell you which direction to go. Also I have a question about your ash dump. The picture doesn't show anywhere for the ash to go other than your air supply tube. This could be a problem if and when a hot ash burns through your flexible tubing. Also it will clog with ash and rob you of your air supply. Mark <>< Quote Link to comment Share on other sites More sharing options...
nathand Posted September 9, 2013 Author Share Posted September 9, 2013 Thanks guys the ash dump on the forge needs to be modified once i get going properly i will adjust In regards to my location i live in SW England, Bristol, there is a local smith i think i might ask if i can have a look at there shop here are some more photos since the photo on my first thread ive lowered the hood but im still only guessing what is the best height?? Quote Link to comment Share on other sites More sharing options...
DSW Posted September 10, 2013 Share Posted September 10, 2013 From what I can see it looks like your exhaust duct is way too small. Trying to push large volumes of air thru long lengths of small ducting usually causes the blower to over work and overheat. Part of the cooling for the blower is the air passing thru the unit. If the fan can't push enough air thru the small duct work, it over works and can't cool itself down properly. 3" is tiny. 6-8" is probably minimal at best. Ducting is rated at a maximum flow volume ( in the US it's CFM or cubic feet per minute in Europe I'd guess it's in liters) Fan size and duct size have to be matched. If anything have the duct size exceed the fan rating. Note that bends and longer lengths increase drag, and reduce flow. Also corrugated duct work causes more drag than smooth ducting also decreasing max flow. Lack of exhaust flow will kill you if you are running a forge in an enclosed space. At a minimum I'd strongly suggest installing a CO alarm. Keep in mind CO is heavier than air, so installing it at ceiling level means by the time it goes off it may no longer matter to you since you will be unconscious. Quote Link to comment Share on other sites More sharing options...
Glenn Posted September 11, 2013 Share Posted September 11, 2013 Make the duct work as short as possible and as straight as possible. Usually 8 inch is minimum (read as maybe works) with 10 inch and 12 inch being most recommended. You can make a much larger diameter chimney, then blow fresh air into and UP the chimney creating a suction in the smoke chimney. This should keep the fan cool(er) and clean(er). Remember to keep the new chimney equal to or a bit larger then the cross section of both smaller chimneys. If you have a chimney cap, remove it when you are using the forge. You do not need the restriction to the air flow. Quote Link to comment Share on other sites More sharing options...
nathand Posted September 11, 2013 Author Share Posted September 11, 2013 thanks for the help guys the duct an fan in the photos are 4 inch, but like you guys have said this is too small i am now thinking on the lines of a 12 inch chimney then use the 4 inch fan that i already have to also blow air up the chimney which should keep it a lot cooler i will have to adjust the hood for 12 inch do any of you guys know what the best size to make the hood is???? is it in relation to the forge???? and what is the best height to set he hood above the forge???? thanks again Quote Link to comment Share on other sites More sharing options...
Glenn Posted September 11, 2013 Share Posted September 11, 2013 Side draft chimney works better than a hood. Build the chimney to work on its own without the added in line fan. Just be sure there are no obstructions within 10 feet of the outside chimney and the top extends at least 3-4 feet above the roof. Take into account any prevailing winds, buildings, trees etc that would effect the air currents. Quote Link to comment Share on other sites More sharing options...
ThorsHammer82 Posted September 11, 2013 Share Posted September 11, 2013 A properly designed Chimney doesn't leave much risk of lighting the roof on fire. Most are double walled and insulated. YOu should be able to just buy the "through" section at a local stove/fireplace store. Maybe even a hardware store. Quote Link to comment Share on other sites More sharing options...
nathand Posted September 12, 2013 Author Share Posted September 12, 2013 Thanks guys in terms of building a chimney i wouldnt know where to start, im going to go for a hood for now just because of the fact that my set up is a temporary one until i get a bigger place, then i can build a decent brick chimney, i know its not the best solution but im desperate to get up and running, all be it without setting fire to the place or choking myself out, ive been looking for 12 inch chimney flues but have had no luck so far, im thinking of making one out of some cement lined ductile iron pipe???? it heavy but theres lots of it where i work and its free I just need to get the correct hood size now Quote Link to comment Share on other sites More sharing options...
nathand Posted September 12, 2013 Author Share Posted September 12, 2013 Guys ive got it, been searching old posts and I am gonna build the super sucker side draft chimney a take all the old stuff down Quote Link to comment Share on other sites More sharing options...
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