Swapping an old Airtronic for a newer generation Airtronic.

The Airtronic S2 and Airtronic S3 heaters are interchangeable. The first generation Airtronic cannot be directly replaced with a newer generation heater because of wiring differences.

The dimensions, fittings, and ducting are the same for all Airtronic generations, so you could replace a 1st generation Airtronic with a 3rd generation Airtronic if you also replace the wiring.