My Husband has take several classes in heating and air. We are getting ready to install a heat pump into my dad's house that we bought from him, it's an older house, and we have done some extensive remodeling. Right now it is using propane gas, and it's a killer. Can you explain how to put in a 4 ton heat pump and air exchanger. The house has around 1900 sq feet.

I suggest you take a class in HVAC or do a Google to find a book on the subject. This subject can take a very long time to explain.

Make sure to get your refrigerant licensing sqaured away before attempting to install the unit yourself. This type of install requires many tools and much knowledge in the field of hvac. Your best bet would be to hire a pro to do the heat pump part of the remodel. Its just impossible to help from here. Wish you the best of luck and please let us know how the install goes.