That model thermostat is meant to be use as a low-voltage hvac controller. Meaning its outputs are to be used to control relays, and not directly drive loads (like heaters and compressors).
So to cobble together a heater controller, you'd need to add a 110vac to 24vac transformer and a relay with a 24vac coil and points sized for your heater amperage. Then, with the thermostat set for heating mode it would switch the relay which would carry the heater load.
By the time you combine the transformer, relay, and a box to hold everything, the cost might make an STC-1000 look pretty good...