I would like to install a wood burning cookstove in my kitchen. I can't go through the ceiling/roof so I must go out the side of the house. But the house is made of granite. I do have a vent hole above a window right next to the ceiling. But to do that I need a 90° turn from the stove to the outside. Being next to the ceiling, I'll need Class A pipe. But I can't find a Class A 90°. Is there a source for this out there? Or is there a different way to go about this?