I just had a new Trane 15i heat pump system installed. I still have my old oil fired boiler, and it works OK. They installed a heat exchanger for the hot water from the oil boiler just after the new Trane air handler.
The installers claimed that my new heat pumps are so great, I should never need to use my old oil boiler. However, they showed me that I just had to manually change the system setting on my thermostat from "heat" to "em heat" if I ever wanted to use my oil boiler.
I have the Trane 820 thermostat, which I believe is just a re-labelled Honeywell Pro 8320.
I reading up on the thermostat, I found that it could be set up to automatically switch between my heat pump and my oil boiler based on outside temperature. I went there and added the outside temperature sense, and modified the thermostat's installer settings. For example, I set "0340" to "02" and "0350" to "35".
I watched that evening as the outside temperature drop below 35deg, and yep, my heat pump compressor turned 'off' and my oil boiler turned 'on'. Great!
However, after a few seconds, I realized that the fan had turned 'off' too, when the compressor turned 'off'.
Not good. I need the fan to continue to run. BTW, the fan does run when I manually select "Em Heat".
I went back and started to re-read all the docs I had. I then found this one paragraph in the thermostat's installation manual, in the section dealing with having the thermostat control fossil fuel aux heating.
So, apparently, the fan (G terminal) not being energized is proper operation.OPERATION IN HEAT MODE BELOW BALANCE POINT
When the outdoor temperature is below the selected
Balance Point Temperature (ISU 0350), only the Fossil
Fuel (auxiliary heat) operates and the fan (G terminal)
does not energize when the comfort control calls for heat.
Is there anyway around this? Is there some other installer setting that could get changed to allow the fan to run when I am below my set balance point? Fan control, "0180", looked promising, but it isn't offered.