https://www.minisplitunit.org/

9000 Btu|3/4 Ton|(under 400 Sq Feet)

12000 Btu|1 Ton|(400-600 Sq Feet)

18000 Btu|1.5 Ton|(600-800 Sq Feet)

24000 Btu|2 Ton|(800-1200 Sq Feet)

30000 Btu|2.5 Ton|(1200-1500 Sq Feet)

36000 Btu|3 Ton|(1500-1800 Sq Feet)

48000 Btu|4 Ton|(1800-2000 Sq Feet)

60000 Btu|5 Ton|(Over 2000 Sq Feet)

How old is this equipment? Is the same contractor doing the removal and installation? Approximately where are you located?

In general reusing HVAC is a bad idea. It rarely works especially for the AC condenser and coil. The 100K BTU furnace sounds over sized for your house especially if a high efficiency model. An over sized furnace will short cycle, waste fuel, and potentially have a shorter life. I have never seen two condensers connected to one furnace. That would be a unusual configuration. I question whether the furnace could provide the proper air flow. It is difficult to say whether the 2.5 or the 3 ton would be the appropriate size. This could be an expensive reuse of the equipment if the AC uses R-22 refrigerant.