Does your Grandpa have a baffle in it? I've been messing with a baffle in mine(size, angle, height). I've got a couple issues with mine I need to take care of or else my old stove is going back in. I really want to make this Fisher work because of the larger firebox.
I do believe my mamma bear has the angles for to put in a baffle but the chimmly is short so I just keep the wood to the front and allow natural convection to utilize the heat more thoroughly with the fire at the front