Venting size question

[Julie312]

Very newbie here, both to this form and wood stoves in general. We recently purchased a raised ranch that came with a wood burning stove. A quick description of the setup: standard fireplace upstairs with external masonry chimney and directly beneath it on the lower level is where the wood burning stove is venting up the chimney, each with their own flue. The home is roughly 2000 sq ft, 1000 upstairs and 1000 downstairs. The wood stove it came with was installed in 1991 and in pretty rough shape. We recently purchased the Summers Heat 2400 sq ft wood burning stove from Lowes model #50-SHSSW02 made by the Englander company. Now we get to the problem, the black stove pipe was in rough shape as well so we scrapped that and were all set to install new stove pipe but after pulling it out their setup seems odd. The stove vents to an offset chimney hole that is 8 inches in diameter but the stove pipe is 6 inches in diameter. They have the stove pipe through the chimney hole back to the flue and fiberglass insulation around the stove pipe to account for the diameter differences. This seemed odd. Is there something specific we should do to account for the hole in the masonry being 8 inches with a 6 inch vent pipe? I attached pictures of the general setup. One is messy from us pulling it all apart with the old stove in the pic and the other is from the listing when it was fired up to show the setup they had going. Any advice at all appreciated.
TLDR: 6 inch stove pipe through 8 inch chimney hole okay?

 

[begreen]

Has the flue behind the stone wall been cleaned an inspected to verify it is ready for a stove? What is the inside diameter of the chimney flue? Also, is there a cleanout on this flue and if so, is the door sealed?

 

[Julie312]

The flue has been cleaned and is good to go integrity wise. I forget the exact dimensions but is larger than recommended and they suggested lining with 6inch. Our plan was to line the flue with 6inch during the summer as there is only at most 1 to 1 1/2 months of burning weather left here and we have bigger fish to fry with our move in. Previous home owners used their wood stove seemingly with decent draft as they were burning until the day they moved out. There is a cleanout on this flue that isn't airtight. Yet another thing on our to do list.

 

[begreen]

You can use some 1" stove door gasket to seal the gap around the pipe. Then seal the cleanout door with silicone. Just run a bead around the edge and close the door on it. The stove will work better with a properly sized liner. Be sure to clean out the flue again before adding the new 6" liner.