Mr Fix It Plumbing 4320 Atlantic Ave #230, Long Beach, CA 90807 (562) 988-2454 http://www.mrfixitplumbing.com/ A combustion air opening within an exterior wall of one-sq.-inch for every 4000 Btu ranking of h2o heater is necessary within the upper and reduce 12 inches of your enclosure. J&D Plumbing & Heating https://www.google.com/maps?cid=4067949459714107514