Recommended Tankless Water Heater for a 2021 Grand Design Momentum
Updated 11/17/2025 | Published 12/12/2024
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Question:
Hello! This is Max with Johnson RV in Fife, Washington. A customer is inquiring about replacing a 12 gallon Suburban hot water heater with a tankless model. I measured the Suburban door which is 15x15. The trim plate that surrounds the water heater door is 18x18. Does this mean I would order the 15x15? If so, will it come the decorative trim cover plate? The coach we would be installing it on is a 2021 Grand Design Momentum.
asked by: Max M
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Expert Reply:
Hey Max! It does sound like you need a 15"x15" hot water heater. The closest option I have with a 18" x 18" door is going to be the Fogatti InstaShower 7 RV Tankless Water Heater item # FG46FR. This one is designed to replace a 10 to 16 gallon tank water heater. It fits a cut out dimension of 13" wide x 13" tall x 13-13/16" deep.
I have linked a review video below where you can hear all the features of this water heater discussed.
Product Page this Question was Asked From
Fogatti InstaShower 8 Pro RV Tankless Water Heater w/Mixing Tank - 55K Btu - 15"x15" Door
- RV Water Heater
- Tankless Water Heater
- Gas
- 40001 - 55000 Btu
- 12 Volts
- 13L x 13W x 13-13/16D Inch Cutout
- 16-3/8L x 15W x 15D Inch
- Black Door
- Fogatti
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Jerred H.
11/17/2025
Hey Max, how did the fit go with the Fogatti InstaShower 7 on that Grand Design Momentum? It’d be great to know if the 18x18 door lined up well with your existing opening. Your update could make it easier for others working on similar replacements.