I am going to have a heat pump installed. I have heard good things about Trane heat pumps, and I have decided upon that particular brand. I am not sure which model to purchase though. Does the model that you need depend on the square footage of your home alone, or are there other considerations? I want to have the correct model installed, so the unit will perform at its best. Are there different models for different climates and environmental conditions, or do all models have the ability to function in any type of weather?