Load calc s have only come into their own in the last 10-15 years.
Before that there were no calcs done ande if a contractor wanted to soundv hi tech he counted alum siding as insulation.
Insulation codes came into being in the 1970's.
Before calcs furnaces were sized by the "bettor to be too big than too small method"
Non contractors swimply would not believe the number of 100,000-120,000 btu units that we collectly have torn out of homes and replaced them with 45-50,000 furnaces.
I had one job where two janitrol 120.000 furnaces were twined and I took the both out and replaced them both with one 60m hi eff furnace.
A/cs were all sized by rule of thumbs like one ton per 500 sq feet,or 600 sq feet.
I don't know for a fact but I can guess THAT THERE HAS NEVER BEEN A LOAD CALC DONE ON YOUR HOUSE. As far as insulation is concerned you probably have the minimum requirements done because it was 1989.
To the fellow that laughed at asking for the blueprints,I used to ask.Not everyone has their blue prints and you would be surprised at how many do.If I had them the load calc just went so much quicker and smoother.I'd say it cut at least an hour off the time required.