I'm having my new heat pump (new install) put in sometime this week. It was suppose to be done today, but it's done nothing but storm. So, I figured I'd take this chance, on the off hand I am around when they do come to install it, to ask some questions. Basically, anything I need to look for or specifcally request during the install? This is going to be a 4 ton, completely external unit, with 2 returns and 1 supply ducted out the foundation to the unit. I know I want that ductwork to be well insulated, and the space around the ductwork and foundation opening to be sealed from critters, but is there anything else? It has a bimetal thermostat already in place, which I'll be replacing with a new electronic heat pump thermostat when I move in.

Hello and thanks for offering so much valuable info. I am getting prepared to replace a split system heat pump in my home and need some info/advice. I have done a heat gain/loss calculation using computer software based on Manual J. Results are 25k btuh total gain and 45k btuh loss. Design conditions were adjusted for my area(Central Alabama). Considering that this is around 2-2.5 ton load, my current unit is a 3.5 ton. This is a 2400 sq ft single level brick home about 30 years old and insulated fairly well in walls and attic. This load calculation seems very conservative for a home this size. Insulate ducts are located in half unconditioned basement and half crawlspace. It is shaded well, but will a heat pump this size cool a home this size when it is regularly 95-100 degrees in the south?? And will the backup heat engage regularly in winter virtually cancelling my attempts to get the most efficiency out of my new system? Also, assuming that I go with a heat pump of around 30,000 btu, should my backup heat make up only the difference between my unit heating capacity(30,000) and actual heat loss of my home(45,000) plus some margin, or should my backup heat be sized to carry the full load if needed? I have read that 90% of older homes have oversized equipment. Is my home one of them?