A type B gas vent serving a 87,000 btu wall furnace must extend a minimum of how far above where it emerges through the roof of a single family home with a 7/12 slope? Assume the vent is located more than 8′ from any wall.

A type B gas vent serving a 87,000 btu wall furnace must extend a minimum of how far above where it emerges through the roof of a single family home with a 7/12 slope? Assume the vent is located more than 8′ from any wall.