liner/flue extender

Why does it need to be extended? Do you have drafting issues?
What exactly do you mean by a metal flu extender? Is this a masonry chimney? If it is, you are going to have to add a section of Class A to be code compliant. That won't be any different than any other Class A chimney at that point. To do it, you will also have to add an adapter plate, & connect the liner to that plate. The adapter will have to be anchored to your existing masonry, & then the Class A mounted on the plate. Add a cap & you're done. As long as your wood is dry, you should be good to go...

There is no great way of doing this w/out building up that chimney appropriately. Since you are working on this chimney anyway, it simply should be done right now so you aren't kicking yourself later.

pen

That's the correct way to go, if you're not gonna brick to the top.

Got a link? I've looked and not been able to find that.

Here's ICC's Excel version:
http://www.icc-rsf.com/main.php?t=chem_produits&i=7&l=en

Thanks Dak, that looks pretty slick. Doesn't look as though one can purchase through that site though.

pen

No, but there are hearth shops that carry them, at least up here in the Vampire state. They can be used for thru the roof extensions on masonry chimneys, too. That's where I started using them...

Yep. Same product, different manufacturer...

If this is the product, I don't see there being a way to connect the single wall to it.

There's a corrugated extension that comes off the bottom of the plate & that fits inside the SS liner. The liner is secured with to that extension using "Zip" screws...I think you can see it better in the EXCEL version...

Got it, I was expecting a band clamp.

Thanks