I have an existing Honeywell non-programmable thermostat with 2 wires, a white and black. I 'd like to replace with the RTH230B programmable. After reading the Reader's Digest Do-it-Yourself book, it says I would need to add wires if I wanted to replace a non-programmable thermostat with a programmable thermostat. Is this true? I don't want to open the package to see the instructions and not be able to return it if it's the wrong thing.
I have hot water baseboard heat, no AC, and I believe it's low voltage.
Thanks.

Do not see why you would need more than 2 wires. Without AC you only need 2 wires run from the zone-valve to the thermostat.

Some digital thermostats do require a return wire to the other side of transformer. I don't believe that unit does. There are quite a few posts on that thermostat in the heating and cooling area. Might be a good idea to look over some of them. Can't promise you the directions will be in English when you do open it. You also may need to sort out which wire comes directly from the transformer, and connect it to the RH terminal. Connect the wire that goes to the boiler to the W or W1 terminal.