Is the FAA-350 Popit Base a direct replacement for the Older D290 Popit Base?
No, not a direct replacement. The FAA-350 is only UL Listed with the following, FCP-350-P Photoelectric Smoke Detector. FCP-350-PTH Photoelectric Smoke Detector With Heat and FCH-350-135 Heat Detector Heads.
The D290 was UL Listed with the following, D281A Ionization, D282A, D265AW Photoelectric Smoke Detectors, D283A Photoelectric Smoke Detector With Heat, and D254/D255, D56/D257 Heat Detector Heads.