The 20-gallon water heater is the upper-tier point-of-use size — sized for single-occupant ADUs, pool houses, RV park-models, small cabins, and tiny homes. The 20G supports a full normal shower (5–7 minutes at 2 GPM) plus 1–2 hand-washes before recovery — adequate for 1-occupant whole-bathroom service.
Top 20-gallon picks
20G applications
- Single-occupant ADUs / mother-in-law suites / garage apartments
- Pool house bathrooms with daily use
- RV park-model trailers
- Small cabins in mild climates
- Tiny homes with 1–2 occupants
20G vs 30G vs 10G
- 20G vs 30G: 30G adds 10 gallons for ~$50 more. If you have full vertical clearance, 30G is better sizing.
- 20G vs 10G mini-tank: 20G supports a full shower; 10G is for occasional small-bathroom or under-counter use.
- 20G vs 6G under-sink mini-tank: 6G is single-fixture only.
Bottom line on 20-gallon water heaters
The 20-gallon water heater is the small-room whole-fixture electric — right for ADUs, pool houses, and small cabins serving 1 occupant. The Rheem Performance 20G is the volume pick. For higher capacity, step up to 30-gallon. For under-sink applications, see point-of-use mini-tanks.