Most of us here feel a good 2 stage stat is the only way to get the best comfort out of a 2 stage furnace. The timer eliminates the best feature of a 2 stage, long run times on gentle, quiet low in bitter weather.
The B is the width, 17.5"
The 8320/8321 can handle 2 stages of heat pump compressor and 1 stage gas backup or it can handle 2 stages of gas heat and 1 or 2 stages of cooling.
My guess is you have some screwy polarized media air cleaner, like a Dynamic or Airscreen.