Natural Gas Appliances Standards Act of 2023 or the Natural GAS Act of 2023 This bill modifies energy efficiency requirements under the Energy Policy and Conservation Act to limit what the Department of Energy (DOE) may include in future rules related to the following natural gas appliances: gas water heaters, furnaces, boilers, kitchen cooktops, ranges, and ovens. Specifically, the bill requires DOE to certify that rules are not likely to result in a significant shift from gas appliances to electric appliances. DOE must also require a full fuel cycle analysis for energy efficiency standards as part of the rulemaking process. In addition, the bill exempts certain small manufacturers of major household appliances from future energy efficiency standards for such appliances. Future rules for such appliances must require energy efficiency labels displayed at the point of sale to disclose full-fuel-cycle efficiency rather than point-of-use energy consumption. The bill also prohibits any future rule relating to kitchen cooktops, ranges, and ovens from limiting the features (e.g., quick-to-boil times) and functionality available on residential gas kitchen cooktops, ranges, and ovens.