HVAC system,
This is my furnace in my house, I agree that there are many different systems out there and this portion of the home inspection job is one of the more difficult or unfamiliar areas for me personally. This (picture I have attached) is a high efficient furnace and the one quick and easy way to identify a high efficient furnace would be the two PVC pipes coming from the furnace. You’re mid or low efficiency furnaces will have double wall tin pipe used for the exhaust.