You can replace the Atwood RV Water Heater AT94022 with the Furrion RV Tankless Water Heater # FR93FR, so long as you have the needed space. According to the instructions, which I have linked for you below, this Furrion unit simply requires the opening to be 12-5/8” tall, 12-13/16” wide, and at least 23-1/2" deep.
The Atwood # AT94022 measures 16" tall, 15-1/2" wide, and 20-7/8" deep, so it is taller and wider, so you should have the space; the Atwood also uses a 17-3/4" tall x 18" wide... view full answer...