Advice needed - Installing smart thermostat but old one only has two wires

As the title says, I have a roughly 12-15 year old Lennox forced air system with a pretty basic thermostat. I would like to install a new Honeywell Smart WiFi thermostat however there are only 2 wires heading back to the furnace and neither is the Constant 24v.

Old thermostat (blue wire does not make its way to the furnace): http://imgur.com/VO7YauR

Furnace hookups: http://imgur.com/QP5Q1hd

New Thermostat: http://imgur.com/vR1WSSP

My hope is to just re-run the wire into the basement and hook up to the furnace, and then wire the new thermostat. I just don't know if that will cause problems with the furnace. If it's anything more than replacing the wire I'll just hire someone to do it but this seems simple enough in thought.

submitted by /u/duluthbison
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