Blacksmith39 Posted December 21, 2021 Share Posted December 21, 2021 For a while I’ve had a smoke problem in my shop. My shop is too smokey almost all the time. I have a large Centaur Forge hood and an 8” stove pipe. My chimney doesn’t go straight up through the roof as I’ve seen a lot of blacksmith shops do. It goes through the side of my shop then straight up. I really am not sure what to change to make my chimney draw better. It’s like it just can’t draw all the smoke, only some of it. That makes me wonder if I just need a larger stove pipe but I wanted to ask opinions before I just start trying everything. Hope someone has some suggestions. It is much appreciated! Thank you!! Merry Christmas Quote Link to comment Share on other sites More sharing options...
Frazer Posted December 21, 2021 Share Posted December 21, 2021 Do you have any pictures you could share? Both of the forge/hood setup inside and an exterior shot that gives an idea of the building, the chimney height and its surroundings. Quote Link to comment Share on other sites More sharing options...
Glenn Posted December 21, 2021 Share Posted December 21, 2021 Is this what they call a half hood? First, open a door or window to make sure you are getting enough air INTO the shop to make up the amount of air that is going up the chimney. A 8 inch circle has an area of 50 square inches A 10 inch circle has an area of 78 square inches A 12 inch circle has an area of 113 square inches The suggested chimney size for a solid fuel forge is 10 inch and 12 inch in diameter. It is suggest that you use 2 ea 45 degree bends instead of a 90 degree bends so there is less restriction in the air flow in the chimney. A straight chimney is preferred as a horizontal run can kill the draft. The top of the chimney should be 4 feet above anything within 10 feet of the chimney. Check for any air currents or eddies that may be caused by buildings, trees, or other objects that would affect the air flow around the chimney. As frazer said, we need photographs before we can make any suggestions. Quote Link to comment Share on other sites More sharing options...
Frazer Posted December 21, 2021 Share Posted December 21, 2021 My forge had a half hood on it when I bought it (not from centaur forge). I took it off since the fire would have been so far from the chimney opening that there would have been a long way for the smoke to travel and cool down before it (hopefully) reached the hood. I think it was intended to be used outdoors or in a very open shop space where if not all the smoke was captured it wasn't a big deal. 8" isn't ideal, but with the right setup it can be made to work. If it is the half hood I'm inclined to think that's the biggest factor, but I'll hold out for pictures before I just start making assumptions. Quote Link to comment Share on other sites More sharing options...
Blacksmith39 Posted December 21, 2021 Author Share Posted December 21, 2021 Sorry I forgot to add photos. Here are a few. My shop is very open and has lots of airflow so I don’t think that’s the problem. Thank you everyone for all the input so far! Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted December 21, 2021 Share Posted December 21, 2021 Is that a cap on the top? If so is it choking the flow some? Also that hood is mainly drawing in cold shop air rather than hot air that will drive a chimney flow. The 90 deg bends have already been discussed. Have you looked at the design of the super sucker for forge use? I have very little escaping smoke and have done pretty much nothing; but 10" diameter chimney with the inlet close to the fire. (I really need to build a super sucker end now that I have electricity to my arc welder!) Quote Link to comment Share on other sites More sharing options...
Frazer Posted December 21, 2021 Share Posted December 21, 2021 Ok, so I think the hood is the main culprit. You could probably modify it somehow to bring the opening down closer to the fire. Hotter flue gasses, more movement of air up the chimney, stronger draw. However, you might be better off leaving it in one piece and building a new hood. I have a modified super sucker design that works extremely well, but it's not the only good design out there. Basically, you want to bring the fire closer to your hood and make it so the path of least resistance for the smoke is up through it, not around into the room. Even if you did increase the diameter of the pipe, you would have to replace the hood since that opening is 8". Easiest thing first, start with the hood. I also can't tell what's going on with the cap. If it's an improvised setup you want to make sure it's not overly restrictive. I've read some specs on caps, but I can't remember them at the moment. Here's my modified super sucker. If you're keeping the 8" pipe (which you are better off bumping it up to 10") you'll have to further reduce the size of the rectangular opening in front. The cross sectional area of the inlet should be smaller than the cross sectional area of the outlet (chimney). Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted December 21, 2021 Share Posted December 21, 2021 If you lower the hood connection you can also try to mount the pipe at a slant instead of on the flat! Quote Link to comment Share on other sites More sharing options...
Blacksmith39 Posted December 21, 2021 Author Share Posted December 21, 2021 I hadn’t even thought about the cap being part of the problem. It definitely could be part of it. I’m going to look into the super sucker design. I had heard of it before but didn’t really know what it was. I am also definitely going to get a 10” or 12” pipe. Quote Link to comment Share on other sites More sharing options...
Frazer Posted December 21, 2021 Share Posted December 21, 2021 I think between those updates you'll be in pretty good shape. One other thing I'll add... As long as you're working on it now would be a good time to rethink that support system you have there. You're asking a lot from that one little strap and I would hate to see the whole thing come down suddenly and unexpectedly. They make telescoping roof brackets for pipe of various diameters as well as standoffs you can use to mount the pipe to the exterior wall. Quote Link to comment Share on other sites More sharing options...
Irondragon Forge ClayWorks Posted December 21, 2021 Share Posted December 21, 2021 The hood is definitely most of the problem. They are easy to modify. Mine uses an 8 in connector to the main 10 in stack. I found reducing the size of the opening solved my excess smoke in the shop. Before... After modification... Quote Link to comment Share on other sites More sharing options...
Glenn Posted December 21, 2021 Share Posted December 21, 2021 Suggestions for minimum of space between the chimney and cap is 1-1/2 to 2 times the diameter of the chimney. Draft can be improved by an inverted cone under the cap (with the 1-1/2 to 2 diameters stand off). This helps divert the air flow out and away from the cap. There is a thing called a high velocity chimney rain cap which is a larger pipe placed over the existing chimney. I do not recall the suggested increase in diameter and length of the outside pipe. The idea is to allow the chimney to produce draft and the outside pipe to act as a booster, sucking and introducing additional air into the draft. By the design it keeps rain from getting inside the inner pipe. Quote Link to comment Share on other sites More sharing options...
Glenn Posted December 21, 2021 Share Posted December 21, 2021 You may want to review the section called Chimneys, hoods, and stacks. Forge Hoods Explained, Chimney size and height, and other topics may be of interest. Quote Link to comment Share on other sites More sharing options...
Blacksmith39 Posted December 24, 2021 Author Share Posted December 24, 2021 Thank you everyone for all the super helpful suggestions and advice! I commissioned a welder I know to make a super sucker forge hood for me. I’m looking forward to finally fixing the smoke problem. I’ll also be adding a better support system for my new chimney. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.