We bought a condo last year that was built in 1977 and need to replace the old electric heat ( 220 Volt ) thermostats. They seem to be a DPST type ( it has an off position ), there are only 2 wires on the back off the thermostat - 1 red with 2 black wires attached and a black wire with a black wire attached. The electrical box on the wall only has 6 wires, 3 black and 3 white that are pigged tail toghter. We would like to install the newer type digital thermostats that have 4 wires, 2 red & 2 black. Can these be installed with this set up. Could the 2 black wires that are attached to the red wire on the thermostat be the 2 coming from the line side of the panel??

Check with the condo's association before you do anything. Typically any electrical work done in a condo has to be done by a licensed electrician.