Manual J is a Fake
Since we can’t actually do a Manual J on an old house because we don’t know the inputs like ACH, Duct Loss, etc, we just use guesses that make the loads come out the way we want. On a 2400 sq ft house, anyone can create a set of guesses to give you every size ac unit there is.
Since the HVAC Guy” does not have the Blower Door, Duct Blaster, Smoke Bombs, X-ray vision glasses, or economic models that require truing up like the Home Performance professional does, he simply makes the numbers up by doing a song and dance.
The Manuel J Macarena
Start with your hands on your hips:
Determine duct loss by turning your palms up and look at the ceiling for divine inspiration.
Calculate Air Changes by flinging blades of grass in the air like Tiger Woods before hitting a 5 iron.
Sling your Psychrometer and Shake your Money Maker!
Establish insulation with the X-Vision dance move using your fingers like John Travolta dancing on heroin with Uma Thurman in Pulp Fiction.
Now Grab your butt and pull out the phony HVAC performance metrics
Finally, goose your savings at 10% a year over the like of the system, add them all up, average them back to this year, and shake your booty!
You guys are so funny, pretending to calculate something,