Six residential storage type water heaters, including gas, oil, and electric fueled, were subjected to laboratory tests with and without add-on insulation blankets. Performance and safety concerns were investigated. The performance test results were compared analytically to theoretical calculations while the safety related results were compared to applicable Safety Standards requirements. All units were tested with R-ll, blankets and two units were also tested with R-6 blankets for comparison. A review of previous related studies was also conducted.