The Resideo AT140A1018 Foot-Mounted Transformer is a versatile, multi-voltage unit designed to supply stable 24V control power for HVAC systems. Operating from 120V, 208V, or 240V inputs and delivering 40VA, it reliably powers thermostats, zone valves, relays, and furnace or boiler controls. https://www.partshnc.com/at140a1018-resideo-40va-transfmr-120208240-27v