Zeolites are valuable chemical catalysts and excellent sorbents; several reports have used zeolites for chemical gas sensing. This article systematically investigates the gas sensing performance of ion-exchanged Y zeolites. The interactions between zeolites and ammonia can effectively improve their ionic conductivity, and the zeolites are explored as an impedimetric ammonia sensor. The sensor development was supported by a detailed interpretation of the ammonia-supported ionic conductivity, which was deduced from the measurements of temperature-programmed impedance over a wide temperature range and provides an understanding of the sensing parameters (e.g., temperature and concentration of ammonia). The elevated temperature accelerates the kinetics of the ammonia adsorption/desorption, but it reduces the adsorbing capacity of the zeolite. The thickness of the zeolite pellet is a key parameter for determining the detection limit. Ag-Y and H-Y have higher working temperatures than the alkali cation-exchanged Y zeolite. The excellent selectivity of Ag-Y and Na-Y indicates that they are good candidates as practical ammonia sensors.