Do these combustion vents comply with installation requirements?
a. No, they are installed too close to an attic opening. Under the right conditions, the toxic products of combustion might be pulled into the living space.
b. No, the vents should terminate a minimum of 2 feet above any part of any roof within 10 feet.
c. Yes, the only requirement is a minimum height of 12 inches, 18 inches where subject to snow accumulation.
d. Manufacturer's installation requirements vary.