Wood stove retrofit installation: How do I know what components I can keep?

[Oldstove]

Greetings,

The plan is to replace a 1980s wood stove with a new Hearthstone Heritage. The existing stove is vented with 8" single wall in the house, slips into the thimble and clean out (garage), where it becomes triple wall 8" and goes straight up through the roof. It is AmeriVent brand, UL listed, 8 F BT with 2" clearance from the combustibles. Everything is in very good shape. As you probably know better than I do, the Heritage is set up for 6" pipe.

Can anyone tell me if I can vent the Heritage with 8" and reuse my existing system "as is" or how much upgrading I need to do? Want to keep it safe and legal. Are there liner kits available if that's my best direction?

I apologize if this has been beat to death. My search didn't provide any help.
Oldstove

 

[begreen]

I'm concerned that the two 90 deg. turns in the smoke path might create a sluggish draft when combined with the 8" flue. How tall is the chimney on this system?

 

[Oldstove]

The initial rise from the stove to the thimble is about 4 feet. It is between 10 and 12 feet from the thimble to the cap. For the last 12 years we have had very few back draft problems. Today I heard that my existing triple wall pipe might not be suitably temperature rated.

 

[Backwoods Savage]

I'm not sure about the pipe but can tell you the chimney is a bit short. For each 90 degree bend subtract from 2-3' from the existing chimney so you can effectively say yours is effectively 4-6' shorter than the total. But sometimes you can get by with the shorter chimney. Depending upon how far out from the wall your flue is you have a horizontal section. If only the thimble then it usually is no problem but horizontal sections need 1/4" rise per foot of pipe. On the 6" to 8" there are some who do this with no problems but most times it tends to reduce the draft.