This wouldn't work, unfortunately. A lot of insulation has a reflective layer yielding invalid readings from thermal imaging.

There are several other factors like air tightness which requires a blower door to measure and even the number of elbows in the duct system could have an effect. It's a surprisingly complex field. You wouldn't gain anything over a traditional home energy auditor.

The real opportunity is to scrap everything and rethink the system from scratch.