Have an idea for making a venting system in the shop for getting rid of welding fumes. I have an outlet Im planning on using in the floor for part of it. Originally I was going to put a water hydrant in so I have a piece of 4" sewer drain pipe through the cement in the floor. What Im thinking of making is a vacuum system similar to a vacuum cleaner to collect and move the fumes outside. I did a small test with a shop vac which did just exactly what Im looking for. Im planning on putting some metal flexible pipe very close to where a person is welding and connect it to the larger pipe for removal. I figure if a person can collect it close enough to the source would help. Can anyone recommend a strong enough fan to install in or near a 4" pipe for such a project? I don't do a lot of welding, just mainly would be used in the winter when the building is heated.