What I suggest is this, get together with your heating technician to see whether you can lock out the heat pump and whether you can use what I am assuming is the second stage, the gas in the airhandler to carry the heating. We did something like this, the airhandler would call for heat and the heat pump portion wasn't on the generator, so it would call for second stage heat and the gas furnace portion would come on and take care of the heating. What I am guessing is this won't carry your cooling either. Note that the use of natural gas as a fuel source for your generator drops its output to 18kw.