Most thermostats come either low voltage, (24v, where the wire is very thin like doorbell wire) or line voltage (110v or 240v, where the wire is much thicker). Most line voltage thermostats are on very old systems or elecrtic baseboards. Looking at the wires is the fastest way to know which kind of thermostat your system needs.
Honeywell Thermostats can be found at www.supplyhouse.com
