I see several issues
The dust from the shop will enter the return air duct work, UNLESS it's very well sealed, and it will be drawn into the furnace fiter system which is not designed for that much dust. It will then be distributed into all the rooms of the house, not good.
First you'll need to seal all the ductwork in the basement, regardless of any other improvements.
Second, sealing off the furnace itself is a good idea, ONLY if you provide combustion air, if needed. Newer furnaces use outside air for combustion and have no open flames, much better. and safer.
Third, collect as much dust as possible right at the point of origination either with a shop vac connected to the dust ports 2 1/2" , OR with a full blown Dust Collector, 1 HP or large, with 4" hose. Dust and chips are different so a planer will require a DC, not a shop vac. Sanding makes a lot of dust so a shop vac with a small hose attached to your sander port will work best. That's what I do.
Fourth, make a 'whole room' air filtration unit from a squirrel cage blower from a furnace as many here have done or buy a factory built model from Grizzly, Jet, JDS or others. A simple box fan used to cool off in the summer with a filter or 2 on the inlet side is the cheapest route, but not as efficient.
Fifth, an exhaust fan in the wall that recycles the air to the outside will work, ONLY if you don't draw air or fumes from the furnace OR from down the chimney. This will be Carbon Monoxide, or CO which may kill you.
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
Last edited by woodnthings; 03-24-2013 at 02:11 PM.