The minimum insulation requirements are set forth by ASHRAE/IES Standard 90.1b 1992 and by Federal Public Law 102-486, "Energy Policy Act of 1992" (Subtitle C, Section 342a,5,G). As of January 1, 1994, storage water heaters and hot water storage tanks having more than 140 gallons of storage capacity must meet more rigid thermal energy standards. These standards can meet stanby loss or heat requirements if the tank surface is thermally insulated to R-12.5 and if a standing pilot light is not used.

R Value for Thickness of  Foam

1" - R4
2" - R8
2-3/4" - R 11
3-1/8" - R 12.5
4" - R 16
5" - R 20
Energy savings for Various thickness of INIFLEX foam insulation, at various temperature differences