I've got an isert in a prefab fireplace (a42r) -- dealer did not insulate my liner or install block-off - just used insulation at the top and bottom.  They did not block off the air cooling of the original chimney at least.  How bad is this -- it's not quite a slammer but If I had known I would have pushed for an insulated liner.  Insulate now or do it after the season is over?
	
		
			
		
		
	
				
			
	
	
 )  I have about 4 cords of wood seasoning though so whenever we get the stove installed we should be good to go.  I've been hanging around here learning all the time...