I recently converted my furnace over to a 90% VS Two Stage Heat system.
I had a local contractor out to service the unit due to the blower was constantly running at full speed in the heat mode, the issue was corrected the original installer had the wire from the thermostat jumped from W-1 to W-2 on the furnace board. Now the heat is running in first stage and feels comfortable he informed me in order to get the unit set up properlly he needs to install a new two stage thermostat and run a fifth wire from the thermostat to the board.
My question is is the second stage heat and fifth wire required? What is the purpose of second stage heating?