Prevention & Maintenance
How to Size a Water Heater for Your Friendswood Family
October 7, 2026 5 min readBy Friendswood Plumbing Co.
An under-sized water heater runs out of hot water in the middle of your third morning shower. An over-sized one costs more to buy, more to operate, and takes up unnecessary space. Right-sizing is one of the easiest decisions to get right.
Tank Sizing by Family Size
- 1 to 2 person household: 30 to 40 gallon
- 2 to 3 person household: 40 gallon
- 3 to 4 person household with overlapping showers: 50 gallon
- 4 to 5 person household OR 3+ bath home: 50 to 75 gallon
- 5+ person household OR soaking tub: 75+ gallon or tankless
Tankless Sizing by GPM
- Single bathroom, 1 shower: 4 to 6 GPM
- 2 bathrooms, possible 2 showers running: 7 to 9 GPM
- 3+ bathrooms, overlapping shower + dishwasher + washing machine: 9 to 11 GPM
- Large luxury home, 4+ bath, soaking tub: 11+ GPM or dual tankless units
Common Friendswood installs: Rinnai RSC199iN (11 GPM), Navien NPE-A2 Series (11 GPM), Rheem Prestige RTGH-95 (9.5 GPM).
Friendswood-Specific Adjustments
- Large garden tub or whirlpool: upsize one tier
- Teenagers who take long back-to-back showers: upsize or go tankless
- Multiple generations sharing bathrooms: upsize or go tankless
- Dishwasher + washing machine running simultaneously with morning showers: upsize or go tankless
Signs Your Current Heater Is the Wrong Size
- Running out of hot water during the second or third morning shower
- Dishwasher runs with cold water because tank is depleted
- You hear your heater running almost constantly during peak hours