Hello Ejectr. I have a PF100 and am in my third season with it. Generally, it has been great. When first installed it had a bad blower motor and it took a long time to figure out the problem. But I bought a replacement from Grainger for about $150 (it's the three speed motor) and it works great. I had to replace the igniter last season, which really surprised me. Now, I noticed that it is not always feeding pellets even when the red "Feed Motor" light is on. I traced the wiring for the auger feed motor and tapped on the low pressure switch/differential pressure switch and that seems to have improved the feed, though not entirely. I may replace that switch as it's only about $30.
During the installation process (I installed it myself) I had some correspondence with one of the engineers at Harman regarding the thermostat. He finally told me that I could wire a regular digital setback thermostat in series with the Harman thermostat. It has been working well with that setup. In the process of working this out with Harman I learned a lot about how the system works.
A typical furnace, oil or gas fired, is either on or off, and the typical thermostat is basically an on/off switch with adjustable "on" and "off" points. When the temperature falls below the setpoint on the thermostat the furnace is turned on. The furnace immedately fires up at full force. Once the supply plenum gets up to the preset temp, roughly 150 deg F, the blower will start and distribute warm air through the duct system. When the selected temp is reached at the thermostat, the furnace is trurned off, meaning that the flame is immediately extinguished. The blower continues to run until the preset temp for the supply plenum is reached, and then the blower turns off.
However, a pellet or any other wood fueled furnace works differently. The wall thermostat is not an on and off switch. Rather, it is a thermistor, which is a precision temperature sensitive resistor. As the temperature varies, the value of the resistor directly proportional to the temperature. This is part of the electronic circuit board controller mounted on the side of the PF100. Essentially, as the temperature at the wall thermostat ("wall control") approaches the set temperature, the resistance varies, and the controller slowly reduces the feed rate of the pellets, thereby reducing the fire, but NOT extinguishing it. This maintains a much more even temperature in the house, though it does keep the blower running most of the time. In my particular situation, this is big plus as it a large, drafty, very old house. With the oil furnace running we always have cold spots, but the PF100 keeps it much more comfortable. And the blower, though audible, is much quieter than the blower on our oil furnace.
Our PF100 is installed alongside our oil furnace. Either furnace can be operated. The wiring is set up so that only one can be operated at any time. There are four 'shutters' installed in the ductwork. Two of them must be open and two closed depending on which furnace is operating. This greatly improves the efficiency, by only allowing airflow to one furnace. If anyone is interested in more details on this set up, let me know and I can correspond off line.
Doug