I have a Train heat pump and a Lenox hot water heat in our home. The heat pump works well above 40 degrees but I keep having to manually switch back and forth from one to the other. Is there a way to do this automatically?

Many thermostats are set up to handle 2 different heating rtes, and heat pump thermostats have the AUX setting. You will need an outside temperature sensor to make the switch depending on the temperature and a thermostat with an input for it. I can't give you a brand or model.

Yes it is called a low ambient switch. Many Trane units come equipped this way, they call it restricted mode. The wiring isn't to difficult but I would say you should maybe call a pro, a new thermost wire ran to the outside unit may be required.