For the sake of learning.Your heat calc assume tight ducts and you are guessing at the infiltration rate.
Question: infiltration rate; is this referring to the house or duct system?
Question: infiltration; is this referring to the duct system or the building?I was playing with some numbers and your load could be reduced by 3k to 5k btu depending on infiltration and duct gains and losses. My guess is that your house is leaky by the age of the house and the ducts located in the attic.
Question: duct gains & losses; is this referring to insulation or infiltration?
Question: Heat Calcs; does this figure out a duct system to be air/water tight? or is there a % leakage rate entered automatically?
I'm just curious, i'm still learning!