Gas fireplace vent under deck

SO another question regarding a recent inspection. Gas fireplace vent was noted under a deck about 16" down from bottom of deck. Obviously not a great idea but I can’t find any particular documentation regarding proper horizontal install recommendations. One manufacturer even shows it being allowed and only 12" clearance under balcony or deck in their installation manual. Any ideas?

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The answer is what ever the installation documents give for clearances.

Thanks for the reply. I couldn’t determine the manufacturer…