Ján has been working in the field of energy efficiency since 2016, when he started working at the Ministry of Industry and Trade as a policy officer. Between 2019 and 2021, he also worked in the European Commission in the Directorate General for Energy, where he focused on energy efficiency in the heating and cooling sector. Since 2022, he has been working as Director of the Energy Efficiency and Savings Department and is dedicated to drafting national energy efficiency and buildings legislation, strategies and financial schemes to promote energy savings.