I know running a full geo unit on a generator requires a large unit.  Maybe one day I will get one.  For now I have a 5500/6500watt Gen that has worked for years with the old gas furnace.  Has anyone wired up there Geo units to just use the blower circuit and an auxiliary heat source (ie.  wood or gas stove)?  Let me state that I don't want to connect the aux heat source to the Geo unit, only to use the blower to help spread out the heat though the house.  Has anyone tried it?  Thanks.

As long as the generator is of adequate quality to maintain constant voltage within operating range and not spike there is no reason it can't be done. If you have an ECM motor, it is extremely expensive as are circuit boards, so if you are not sure your generator can be trusted, don't use it.
joe

I echo Joe's remarks

There is no reason a 5k generator can't support an ECM blower from a load point of view, but power quality is a concern.

Measurements of AC power quality include total harmonic distortion and frequency. If you plan to plug any other loads (such as refrigerators) into generator beware that cycling of those loads may cause temporary voltage sags, frequency dips, and other distortions that might play havoc with power to the ECM.

I have no idea how robust ECM blowers and their controls are in terms of subpar power.