I have seen 3 furnaces in the past month, installed in the past year, resting on 2" rigid foam insulation pads. Manufacturers installation instructions specify that the only acceptable combustible material below the furnace is wood. I understand that foam provides R value from the cold concrete, and dampens vibration. I do not understand how it passes the building inspectors final walk through.
Andrew, on a final walkthrough by a building inspector, they will look for what was signed off on already on the permit and what hasn’t. They will then focus on what hasn’t been signed off on. In your picture maybe the inspector caught it during the HVAC inspection and verbally told the installer to fix it and signed off on it anyway when the contractor verbally agreed. See what I am getting at? Nothing written about it on the permit notes…