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| The difference is volume of air moved per minute. Shop vacs are made to suck a limited amount or air at a reasonably good negative pressure. Both of the systems you linked move lots of air. The Miller filters, probably through a HEPA filter but the Sears doesn’t – just blows it to a different place.
You can probably make a reasonably good alternative from a squirrel cage fan off of an old furnace feeding a box with a HEPA filter or two. A blower with a three speed motor would provide some adjustment. A 6” transition for stove pipe on a piece of tin screwed to one side of the blower body and a big blast gate valve screwed to the other side. A squirrel cage fan starved for air doesn’t work very well so you probably don’t want to just seal the second side off. 6” ribbed plastic pipe is available from most woodworking stores.
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Welding fumes
