Furnace Chimney - Connecting new stuff to old stuff

[R. Reader]

I was replacing my roof, and the flashing for the furnace chimney was destroyed.  The way the old chimney was put together I was unable to remove the flashing and vent cap. This caused me to have to take apart the venting in the attic.

I'm generally hand enough, and manage to figure most things out once I get into them so I went to my big box store and bought a new vent (double walled to replace the original) Those items basically click together but when I went into the attic to connect it to the old work it wasn't configured the same. 

Please see the pictures below and let me know what type of adapter i need to make the old stuff connect to the new.  Or any other work around?  

 

thanks.

[Jim Katen]

Looks like you're trying to connect an A-vent to a B-vent. A-vents are for woodstoves. 

Take back what you just bought. 

A few different companies make B-vents and they're not inter-compatible. I can't quite make out the brand in your picture - is it Amerivent? Look carefully at the existing vent and note the manufacturer's name, vent type, and size. You'll need more of the same stuff.