I have a potential customer who asked me to install a transfer switch for her. She already has a 5000 Watt generator and I told her she will not be able run her heat with that. She has a heat pump system. (I don't know the exact size of her heat at this moment but, let's say there are two breakers for her heating unit, one a 50A/240V and another a 40A/240V; this is probably pretty close to what it actually is. She also has a heat pump, if I am not mistaken; probably a 30A/240V breaker for that. Do you have to run that also? Or, can you power only the furnace? Can you use the emergency heat setting on the thermostat without damaging the system and leave the heat pump itself off the generator?) I am wondering how to properly size a generator that will handle her heat and maybe four of five more circuits. I really want to recommend something that she will be happy with. Any help will be greatly appreciated.