Will this work for hooking up Tundra?

[WOODBUTCHER]

 

[aokpops]

Is the furnance a down draft ?

 

[flotek]

Mine is hooked up like your first illustration but I use the drolet filter box without hooking up cold air return to the furnace and it works great . In a split level like mine The cool air is drawn down into the basement naturally . the return is unneeded in a lot of these wood furnace applications in my experience