I have a Criterion 2 Furnace with a Rheem SEER 12 A/C unit. Is the furnace considered a multi-stage unit? I bought a Lux tx9000ts digital programmable t.stat and it states that it will not work on a multi-stage unit.Previous home owner lost all manuals and I can't find any concrete info. Thanks.

I have a Criterion 2 Furnace with a Rheem SEER 12 A/C unit. Is the furnace considered a multi-stage unit? I bought a Lux tx9000ts digital programmable t.stat and it states that it will not work on a multi-stage unit.Previous home owner lost all manuals and I can't find any concrete info. Thanks.
If the model of the furnace is RGLH series then it is only a 75 % eff single stage set up.