On the new stainless steel models, the rating plates are located on the side of the heater instead of the front. A larger clearance was required by CSA in order to read the rating plate.
See your installation manual for more details.
A set distance required for proper and safe operation of the heater.
Canadian Standards Association. Approval agency that governs the design and performance of water heaters per ANSI standards. All gas water heaters must obtain a CSA approval before they can be sold in the US or Canada.