Rheem ECM 3.0 Variable speed furnace: Exactly how should it behave?

About my setup, so I just had a new Rheem Prestige 80 two stage communicating variable speed furnace installed. Inside it has a Genteq ECM 3.0 motor, and the furnace is paired with a new Honeywell rth9580wf thermostat. The thermostat is set to auto and is properly wired up to control stage two.

So, I decided to go with the variable speed, however when I very carefully listen to the furnace cycle throughout the day, I notice no variability in speed. I came from a single speed furnace, and this new furnace behaves no differently. I do notice when stage two kicks in, but that is as variable as it gets.

Shouldn\’t a variable speed furnace have a soft start / gradually ramping up to speed and then a soft stop, gradually decreasing in speed once the thermostat temp has been reached? I thought one advantage of variable speed was this gradual flow of air through the system. Some variable speed furnace owners even claim they no longer hear the furnace start up.

I completely understand I likely will not hear a difference in speed if the filter becomes dirty, when the motor has to try a little harder, but I thought I certainly would notice some variability in speed at some point in the normal operating cycles.

So, I called the installer, and he said I simply need to switch the thermostat to fan on. I tried this, but then the fan runs slowly at one constant speed, until the furnace kicks in. That is not variable, that\’s two speeds, maybe three when second stage kicks in.

I called Rheem, and they said, yes, it should do a soft start, however these latest models are so advanced that the soft start is so quiet, it\’s practicaly imperceptible. (I find this hard to believe since, if this was true, I think I would still hear some gradual increase of noise before I hear it really kick in, right?). They also said that I do not need a Rheem EcoNet communicating thermostat to enjoy the benefits of a variable speed motor, and that it would be overkill.

So, please help me understand what the real behavior should be. If it\’s the responsibility of the control board, perhaps there is some dipswitches that control this? Not that I would ever consider touching those, but I looked in the installation instructions, and I didn\’t see any settings relating to this. Could something else be wrong or missing, or do I just need to sit back and trust that it\’s working as designed? I appreciate it!

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