Is the CT3355 thermostat compatible with heat pumps or electric baseboard heating?

No, the CT3355 is not compatible with heat pumps, multistage equipment, or baseboard electric systems operating on 120/240 line voltage. It is also not compatible with gas-millivolt systems. If you have six or more thermostat wires, you likely have a heat pump or multistage system and should return the product to the place of purchase. (Page 4, 7)