Things like the ducts plug right in. Other things like the blower and condenser may need to be swapped out. It also depends on how old your system is. The co

Things like the ducts plug right in. Other things like the blower and condenser may need to be swapped out. It also depends on how old your system is. The controller will probably most certainly need to be swapped out. Do the normal thing with contractors like that. Call 3 different dudes have them come out and give you an estimate. Tell them you want quotes for partial swap out, full swap out, and 3 different price points. Within a couple of weeks you will have most of the knowledge you need if you want to do it. My parents when they switched out they replaced both the indoor unit and outdoor too because they were 30+ years old at that point. Now you probably have NG? If so you can also leave that fairly in place as is. I did that with my prev house. Then have the heat pump for when it is warm outside. Then switch over to NG when it gets to a particular temp. I set it to switch over at about 30F. I could have gone as low as 15 with that unit. It worked decently for most of the time. Where I live it maybe gets in the 20s for about a week a year at most. So the heat pump worked decently. One thing though I would say is if you have a older home especially 1990 or older start with the insulation. It is wildly cheaper to get and gets you part of the way there. Many power companies even run deals where they will help you buy it.