Yes, oversizing will cause you increased load in the calcs.
80K BTU = 23 KW when using resistance heat. So rules of thumb don't work well. Also, is this North Dakota or Florida? Modern double pane low-e windows, insulated doors, R-13 in walls and R-36 in ceiling, and tight construction should make things better than 20-30 years ago. Having a common wall (e.g. it is up against another condo and not exposed to the outside temps) will also reduce your heat loss. A lot of modern construction requires HVAC calcs (see if a Manual J calculation was done, as that will tell you heating and cooling requirements in BTU). A proper Manual J will be done by room so you would know the BTU needs of each room. There are 3.412 BTU per watt (3412 BTU per KW).
An 80K BTU furnace sounds oversized to me for 1400 sq ft condo. That's about what my 3000 sq ft 1960's house in Seattle had (after upgrades to windows and doors).
See the demand factor in the optional calculation. Put in 4 or more separately controlled units and you get the most demand reduction in the load calc.