Economic development and rising welfare lead to higher demand for energy services, which can limit or even negate the results of costly energy efficiency (EE) upgrades. At present, some consumption patterns in Central and Eastern European countries are more sustainable compared to the European Union (EU) average but are rapidly approaching it. Energy sufficiency (ES) leading to an absolute reduction in energy demand will be essential for achieving net zero climate goals, as it will contribute to reducing energy use and the significant investment needs associated with the electrification of the energy system. Various regulatory solutions can be deployed in pursuit of ES targets, but little information is available on the possible impacts on energy use and greenhouse gas (GHG) emissions, especially at the national level. This paper focuses on the residential building sector of two Central and Eastern European countries: Lithuania and Hungary. It attempts to quantify the potential energy demand reduction, associated GHG savings and the resulting change in the energy mix from limiting the per capita heated floor area using scenario analysis with the MESSAGE and HU-TIMES energy system models. The findings suggest that final energy demand could be reduced by 3.6% in Lithuania and 0.9% in Hungary. This would lead to a change in the energy production mix resulting in lower GHG emissions and savings on new energy generation capacity. The results of the research are indicative, as no costs were assigned to ES measures and the calculations were based on assumed levels of ES indicators. However, they suggest that it is worth identifying the consumption segments with ES potential, as a combination of the relevant measures can largely contribute to the achievement of net zero emissions.