The Contractor’s Non-Programmable Choice for 1h/1c Systems features a Large back-lit display, Horizontal or vertical mount, Dual powered: system or battery. Compatible for most single stage 24V heating and A/C systems, 1 heat/1 cool and single stage heat pumps, 2-wire hydronic systems and hydronic air handling systems, Millivolt systems (wall heaters/furnaces, gas fireplaces and/or pellet stoves). Not Compatible With: Multi-stage heat pumps, Multi-stage gas or oil furnaces, 3-wire hydronic systems, 120V/240V line voltage systems (without transformer).