All of the duct work etc has been ran. 

Looking in the crawl space the duct work seems to be fairly new and the plumbing looks good from a quick look under the sinks. 

Most have added room additions during some point in time, so ductwork can not be continuous on any floor. 

I'm also finishing the 2nd floor/attic and will need to put in ductwork.

Of course, to replace means you probably need to install new furnaces and duct work in addition to all of the patching and soffit work that will require. 

Compare that against the cost of having two furnace and air units installed and all Freon lines and duct work ran through the ceilings and floors.If a unit ever goes down in a cold winter or hot summer the tenant has a second unit as a back up to use until the broken one is repaired.You will not have to get the call saying a heroine addict has stolen an entire outside air unit for scrap and you need to replace it asap because its 94 degrees outside.No pilot lights to go out on a furnace. 

I also believed that HVAC had to be ran, but the wholesaler said the duct work was already there.

So yeah big sigh of relief for me- Look I got 20k back in my pocket but I’m out 70k till it sells.The reality sets in- Okay the reality of the situation set in when I realized I had to go do new plumbing, electrical- entire house of duct work because originally had radiator heat coupled with the fact that I changed GC half way thru the process, prior GC got a deposit and I let him walk because of issues with another rehab project so I had to add that loss into my budget.

You might wanna check how the ductwork for the bathfan was done up in the attic.

Here another question for you, which plan should I go for a basic plan or premium that includes central vac sys, duct work, electrical, heating plumbing, plumbing stoppages, and water heater?