Raee, I had same questions with my Carrier. I was under the impression that varible speed meant many speeds. I quess I was wrong. My system starts the fan slowly, only after the condenser has had a chance to supply cold or hot air. It ramps up to speed after a minute of so. It does the opposite on shutdown.

Hi:

New (first winter) Rheem Mod owner here. I'm assuming that your furnace was installed by someone who REALLY knows this furnace.

If your unit was set up properly, it will fire at 100% when starting up cold and start blowing in less than a minute. After that it will likely ramp down to a moderate rate (depending on conditions) and stay there until maybe 1-2 degrees from setpoint, where it will coast at a lower rate.

On subsequent calls, it will fire close to the rate where it stopped. When my unit is at temperature, it will continue to run (on and off) and I can't hear it.

Is it possible that when your contractor installed the furnace, he set it up to run with a single or double stage stat, and when he changed to a modulating stat, did not set it 'modulate'.

You can tell by looking in the lower window. If you see an 'h' instead of an 'H', then you're not modulating.

V
Then, based on your TS setpoint and room temperature, will ramp down (firing rate and blower speed)

Sometimes, it's difficult to detect subtle changes in fan speed. Try standing next to the furnace and listening until the cycle ends.

V

Thanks for your answer, veesubotee, I looked in the window, and it was 'H'-- I wonder if the pattern of coming on at 100% each time has to do with just starting the season, and being on only at night and off during the day--so it is starting over every evening. Yet I'd think that after a few cycles, it would be coming on at the lower speed, as you describe it.
Well, I will pay attention to the cycles and see how it functions over time. Cuffs054, Thanks for answering, I'm glad I'm not the only one perplexed at times!

I just returned home from the gym (10:00 A.M.)and it was deliciously comfortable in the house (stat at 66). I had to look at the stat to tell if it was on.

To clarify what I said earlier, when the unit is coming on after setback, it fires at 100% for a short while, then runs at or below that level, then gradually ramps down, then finally off.

Depending on your home's 'situation', it may take an hour or two until the house and its contents reach that temperature (equillibrium).

After that, with the stat set for fast cycling, with repeated cycles, it will turn on at a low rate since it knows it has to deal with a half degree drop in room temperature.

You may also notice that when the burners shut off (display 0), the fan will continue to run very slowly until it finally stops.

Enjoy.

V