The best tankless gas water heaters include the Rinnai RUC98i, Navien NPE-240A, and Rheem RUC80i, known for efficiency, reliability, and high flow rates.
Tankless gas water heaters provide on-demand hot water while saving energy and space. Unlike traditional tank models, they heat water only when needed, eliminating standby energy losses. This guide compares the best gas tankless units for homes of all sizes.
How Tankless Gas Water Heaters Work
When you turn on a hot water tap:
- Cold water enters the unit through an inlet pipe
- A flow sensor activates the gas burner
- Heat exchanger rapidly heats the water
- Hot water exits through your faucets
The process shuts off automatically when you close the tap. No storage tank means no wasted energy keeping water hot.
Condensing vs. Non-Condensing Models
Condensing Tankless Heaters
- 95%+ efficiency (UEF up to 0.96)
- Uses secondary heat exchanger
- Lower venting costs (PVC pipes)
- Quieter operation
Non-Condensing Tankless Heaters
- 80-85% efficiency
- Single heat exchanger
- Requires expensive metal venting
- Lower upfront cost
Best Tankless Gas Water Heater Brands
1. Rinnai RU199iN
With 9.8 GPM flow rate and 199,000 BTU capacity, this Rinnai tankless water heater handles whole-home demands. Features include:
- 0.82 UEF rating
- WiFi connectivity
- 15-year heat exchanger warranty
2. Navien NPE-240A2
This condensing model offers industry-leading 0.96 UEF efficiency with:
- Built-in recirculation pump
- 11 GPM maximum flow
- Quiet operation (49 dB)
3. Noritz NRC98-DV
Commercial-grade residential unit with:
- 9.8 GPM at 45°F rise
- Stainless steel heat exchanger
- Modulating gas valve for precise temp control
4. Rheem RTGH-95DVLN
Excellent mid-range option featuring:
- 9.5 GPM flow rate
- 0.93 UEF rating
- Self-diagnostic system
5. Takagi T-KJr2-IN-NG
Compact indoor model perfect for smaller homes:
- 6.6 GPM capacity
- 140,000 BTU output
- Simple mechanical controls
Key Selection Factors
Flow Rate Requirements
| Household Size | Recommended GPM |
|---|---|
| 1-2 people | 5-7 GPM |
| 3-4 people | 7-9 GPM |
| 5+ people | 9-11 GPM |
Temperature Rise
Calculate needed BTU output using this formula:
(Desired temp – Incoming water temp) × Flow rate × 500 = Required BTUs
Example: (120°F – 50°F) × 7 GPM × 500 = 245,000 BTU
Installation Considerations
- Gas line sizing (typically 3/4″ minimum)
- Venting requirements (condensing vs. non-condensing)
- Water quality (may need descaling system)
- Local building codes
Maintenance Tips
To maximize lifespan (typically 20+ years):
- Flush annually with vinegar solution
- Clean air intake filter quarterly
- Inspect venting yearly
- Check for error codes
For hard water areas, consider a water softener to prevent mineral buildup.
Cost Comparison
| Type | Unit Cost | Installation | Annual Operating Cost |
|---|---|---|---|
| Tankless Gas | $800-$2,000 | $1,000-$3,000 | $200-$300 |
| Storage Tank | $400-$800 | $500-$1,000 | $400-$600 |
While tankless models cost more upfront, they typically pay for themselves in energy savings within 5-7 years according to U.S. Department of Energy estimates.
