A residential type LP gas furnace has a 6″ diameter vent that penetrates the roof 10` below the ridge. There are no vertical walls within 8` of the vent. The roof pitch is 9/12. The furnace is equipped with a draft hood. What is the lowest discharge opening height permitted for this vent?

A residential type LP gas furnace has a 6″ diameter vent that penetrates the roof 10` below the ridge. There are no vertical walls within 8` of the vent. The roof pitch is 9/12. The furnace is equipped with a draft hood. What is the lowest discharge opening height permitted for this vent?