Humphreys Hammer

Many many thanks to both of you. Sounds like I can build and install this using the existing 10" chimney. Will probably tear down the exiting hood. That will enable me to get easy access to the existing flue to connect the supersucker to it. Landlord is replacing; the flat roof rubber membrane in September so I need to get this done soon. Will keep you posted and thanks so much again.

First, I am super grateful to you for your response. I have looked at the Super Sucker drawing on Anvil Fire and can see that this promises to be a much cheaper solution than an exhaust fan. Has to be the better than what I have now. I hope I am not imposing too much on you by asking a few more questions. 1. If I understand correctly the supersucker concept and drawing, I would have to move the coal forge on which the supersucker is to be mounted so that the supersucker's top opening for the chimney would be directly under the opening/flue of existing vertical chimney. Am I correct? 2. Having so moved the coal forge and fire pot, the supersucker's intake opening would sit on the 1' thick wall of the coal forge, which is 12" inches from the near edge of the firepot? Or should the intake opening be closer to the firepot edge? If so, what is optimal distance from the firepot's edge to the intake opening? 3. If I replace the 10" diameter chimney with at least 12" from the top of the supersucer and through the roof, would it detract from performance to connect the new 12" to the existing 10" chimney above the roof line? Or would it better to dump the 10" inch and install 12" for the entire chimney? In any event, what is the optimal height of chimney measured from the surface of the flat roof?

My existiing coal forge set up includes a hood that is 45x34 at the bottom, 56" high and 34x45 at the top. The 10" steel chimney extends 48" above the hood where it enters the ceiling/flat roof. The chimney extends approximately 12 feet above the flat roof. The distance from the fire to the bottom of the roof is approximately 9 feet. I want to add an exhaust fan. The chimney draws reasonably well but would like to minimize smoke/soot that doesn't get drawn out with this passive hood and chimney. Received a proposal for a fan rated to 650 degrees, but price is $7,000 without delivery and installation. Proposal suggested at least 12 inch chimney and bigger hood. These costs are much more than I can pay. Any suggestions or leads to a less expensive solution greatly appreciated. Shop is in Boston. Thanks