too many unknowns to even make a guesstimate from a forum like this... where will the airhandler or furnace be located?...what about the obvious ductwork modifications that will be required?...I suspect this change from a package system to a split system will be far from economically feasible or justified.

IMO

Like tiger said,cost of new ducts will likly more than offset any operating savings you realize.

Yeah, this question might be specific to my region of the US where we have some homes that use split systems and some homes that use packaged units. I'll call around to some local HVAC businesses and see what they have to say about it. I'm thinking about a heat pump on the roof where the packaged unit currently sits and an air handler in the attic connected to a new plenum, designed to work with the new air handler.

If you have room and can get it off the roof completely over time you could recoup the cost if you go back with a really high end unit like inverter 5 stage, especially in a heat pump system.

Some of the costs you face is because the unit is on the roof, the HVAC contractor has to rent a crane every time some thing large is needed up on the roof to hoist it up there.

The problem with fixing this scenario from a ground stand point is that the copper line set will need to be run from the ground where the condenser sits to connect to the indoor equipment. That can be challenging in a preexisting home.

If there's room in the attic for the air handler to sit the duct work connection work should be quite minor. If the attic is tight with little room, it might not be a good idea. If the house is a two story home and no room in the attic, you're probably stuck with what you have now.

Other feats include new electrical runs to not only indoor equipment, but also the outdoor condenser.

If you don't plan on staying in this home a long time, like 15 to 20 years then you're doing it for the next person. Which if you inform them about what they are buying... may help you sell the house when that time comes. So there is much more to consider here than just what it's going to cost you.

People often go into buying a home 'blind'. There's so many things to think about when buying a home, these kinds of issues are often over looked.

So if your house is competing with another home that has the HVAC on the roof, your house may sell faster... and maybe marginally higher selling point for that convenience. But you have to inform the buyer. In an area with nothing but homes with packs on the roof... done properly and it might prove very beneficial.

Ray, you make a good point. I think I'll discuss this with a real estate agent too and see what they have to say about a split system and the marketability of a home. ROI factors into every decision.