I have a 2.5 ton AC in my 90s house on the border of zone 5/6a that is getting old so I am trying to come up with a replacement strategy. I’m trying to slowly electrify things so replacing it with a heat pump seems like an obvious choice. Using the heat load estimation calculation here https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new and based on runtime data from my thermostat is looks like my design heat load is around 36-38kbtu. I see I could find a cold climate heat pump that would cover that on its own, but I think my limiting factor is my ducts. With my current AC set to 350cfm/ton my tesp is already over .8iwc (I think it is around .9iwc, sometimes gets up over 1iwc if the filter gets dirty). I assume trying to rework the ducts to accommodate a 3 ton heat pump would be cost prohibitive? I was thinking it might make sense to instead just size the heat pump for the cooling load which I assume would still cover most of my heating and I would just use the existing gas furnace for colder days. I imagine another option would be to split my second floor and the rest of the house and have two heat pumps for each zone, but I think that would probably also mean conditioning the currently vented attic so I could put the air handler up there for the second floor, which I would be concerned is a bigger project than it is worth. Anyone have some insights as to what would be the best option here, or maybe an option I haven’t considered?