Does heat loss calculation changes with time?
I have a copy of the original heat loss of the townhouse when it was built in 1983. I need to install new HP/AC system due to the age of the outside unit (1983), and many of the contractors will use the existing calculation. I'm in central CT.
Is this OK?

Here’s the data:

Design condition:
Outside temp: summer 95F, winter 0F
Inside temp: summer 75F, winter 70F
Daily temp range: summer 15-25F, winter n/a
Summer swing temp: 4.5F, winter n/a

SqFt: 1438 (1st floor, 2nd floor)
Type: Multistory
Exterior walls: frame, 3.5 inch, R-11
Windows: double pane, weather-stripped double hung
Doors: sliding glass door weather-stripped

First floor: over unconditioned space
Insulation: no insulation

Ceiling: under vented roof or unconditioned space
Insulation: (not legible). I personally checked the space, and seems to be about 4-6 inch of lose fiberglass.

Heat loss: 27,980

Heat gain: 16,261

The current system is a 1983 carrier 2.5 ton (mod.#38RQ0033400), air handler is a 3.0 ton carrier (replaced in 1994 by previous owner) mod# FB4ANF036000ACAA, with 10kw electric strip.