Read the installation instructions and warnings (I think there are even labels to this affect on the gas water heaters themselves) and you will see that the manufacturers do not 'recommend' that the water heaters be installed in garages *ANYWAY* ... even IF raised up 18 inches.

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Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )