I have two thermostats in an old rancher. One is a older model Bard T87F (before Honeywell put their name on it) which only controls the 26vac tank less oil burning heater with just a red and white wires. The second is also a Honeywell T87F wired with green, white, yellow and red wires and controls the attic unit and outside heat pump for cooling only. The latter transferred to a new digital Honeywell RTH6300B programmable thermostat as per instructions. This is working well but I need to incorporate the two wires from the old Bard into the new digital t-stat for heat. How can I do this? Thanks...

If you have separate transformers, connect the red wire from the heater to RH or R removing any jumper to RC where the red from the heat pump should be connected. Then connect the white wire from the old thermostat to the W terminal of the new thermostat.

If it is fairly easy to run wires from one unit to the other, I would eliminate one transformer, connecting the other's red wire to both RH and RC. You would then need to connect the common on both units to complete the circuit.

Thank you for your help. What you advised makes sense unfortunately the running of the wires is difficult in this house. What I finally did was buy two cheap digital t-stats and just replaced what was there. I still has two t-stats hanging on the wall, but it works. Thank you, talk to you on the next project.