Crematorium
After recent problems with a crematorium, I would not trust the manufacturer to provide any assistance, or to think carefully about where/how the equipment is being installed. The building owner (veterinarian) that I'm dealing with nearly burned his building down.
To be practical, I would recommend a minimum one-hour rated room, and a large fan/exhaust sytem for a moderate-sized room to keep the room containing the equipment to something less than 125 degrees. See Table 508.2, 400,000 Btu furnace requires one-hour separation.
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AIA, NCARB, ICC, NCOA, CSI
ICC Plans Examiner