I had the blower wheel and blower motor replaced 2 summers ago by a service tech (Lennox furnace with A/C). I didn't notice at the time but the tech replaced the five speed (five speed taps) 1/2 HP motor with a 3 speed (3 speed taps) motor.

More importantly I see the tech wired both the heat and cool lines from the controller to the black (the high speed) wire of the motor and just capped off the low and medium speed lines of the motor.

On my other furnace (with original blower) the heat line goes to the medium speed motor tap while the cool line goes to the high motor speed tap.

I am going to borrow an electronic thermometer to measure temperature rise from return to supply plenums and compare to label inside the furnace.

I guess my question is how important is getting the speed right on heat cycle? Obviously if it’s too high the air will not have as a high a temperature rise but in the grand scheme of things does this make a big difference on efficiency or comfort? I don’t know if I should consider this a major failing of the tech or just a common practice.