On Fri, 5 Sep 2008 12:34:19 -0700 (PDT),
wrote:

I'm thinking of the upcoming winter when I need to, as my wife puts
it, bond with my welder. So that means welding in the basement, for
which I know I need a fume exhaust system. As usual, I intend to
build my own cheap. The surplus store has a pretty good selection of
blowers, but I have no idea what size I need (CFM). Can anyone help
me here?

The room you weld in HAS TO HAVE totally sealed and properly drywall
walls and ceiling, primed and painted to protect the paper outer
layer. There is both radiant heat, flying sparks, and flying white-
hot weld metal "dingleberries" that can catch walls and ceilings on
fire.

All access hatches in the walls and ceilings for plumbing or HVAC
need to be non-combustible metal.

I would suggest fire sprinklers for the basement room you will be
welding in, even if you buy the heads from McMaster and braze up a
system yourself out of copper pipe. Flow switch and alarm bell, and a
shutoff ball valve & drain valves for repairs.

I'll do this when I build the little closet around my air compressor
- too much heat in too small a space is a recipe for trouble.

For fumes, if you will be working on little projects on a welding
table, they make tables with a grid top and a pan to catch the slag -
and you can easily attach a duct on the bottom and suck the fumes down
through the table top and outside.

Make the first few feet of the duct with the solid sheet-steel duct
or segmented elbows turning to go up the back wall, in case any
dingleberries get inside - they'll melt right through vinyl dryer
ducting, and the aluminum foil flex duct won't last too much longer.

They make "Inline" or "Duct Booster" fans that splice into a section
of 4" (dryer) ducting, and can handle some reasonable static
pressures. Send the fumes outside like you would rig up a dryer
exhaust. And put a range hood over the table to get the fumes that
still insist on going up.

-- Bruce --