The best gas tankless water heater in 2026 is the Navien NPE-2 240S — a condensing unit delivering 199,900 BTU/h, a 0.96 UEF, and 5.4 GPM at a demanding 77°F temperature rise, with a built-in recirculation pump and 15-year heat exchanger warranty for $1,600–$1,900. For propane homes, the Rinnai RU199iP offers the same 199,000 BTU/h output in a proven LP configuration.
Gas tankless units outperform electric models on one critical metric: flow rate. Where the most powerful electric unit maxes out at 2.7 GPM at 77°F rise, gas condensing units deliver 4.5–5.5 GPM at the same rise — enough for two showers running simultaneously in any climate.
Why Gas Over Electric for Tankless
The physics are straightforward. Natural gas delivers roughly 100,000 BTU per therm. A 199,900 BTU/h gas burner can raise water temperature faster than even a 36 kW electric element. Here's the raw heating capacity comparison:
Gas wins on raw throughput. Electric wins on conversion efficiency. For whole-home hot water in cold and moderate climates, gas is the only practical choice.
Natural Gas vs Propane (LP)
Most gas tankless heaters come in both natural gas (NG) and liquid propane (LP) variants. The LP version has modified gas valves and orifices calibrated for propane's higher BTU content per cubic foot (2,520 BTU/ft³ vs 1,030 BTU/ft³ for natural gas).
Key differences:
- Fuel cost: Natural gas averages $1.10–$1.50 per therm nationally. Propane averages $2.50–$3.50 per gallon (91,500 BTU/gal, or about $2.73–$3.83 per therm equivalent). Propane costs roughly 2–3× more per BTU.
- Gas line sizing: LP models can use slightly smaller gas lines because propane is denser. But most manufacturers still specify 3/4" minimum.
- Availability: About 48 million U.S. homes use natural gas. About 7 million use propane, primarily in rural areas.
- Performance: Identical BTU output and flow rates between NG and LP versions of the same model.
Propane users: Your higher fuel cost means the payback on a condensing unit is even faster. The 0.93-to-0.96 UEF jump saves $100–$200/year on propane — that's a 2–4 year payback on the condensing premium.
Top 10 Gas Tankless Water Heaters for 2026
Condensing Models (UEF 0.90+)
Non-Condensing Models (UEF 0.80–0.85)
Detailed Reviews
#1: Navien NPE-2 240S — Best Overall
Why it's #1: The highest combined score across our five criteria — efficiency, flow rate, warranty, value, and features.
The NPE-2 240S is Navien's second-generation flagship. The dual stainless-steel heat exchangers resist corrosion from both combustion gases and hot water, unlike single-exchanger designs that can develop pinhole leaks. The 0.96 UEF is verified by AHRI testing and qualifies for the 30% IRA tax credit.
The built-in ComfortFlow recirculation system includes a buffer tank and pump — no aftermarket recirculation kit needed. NaviLink Wi-Fi control lets you set recirculation schedules, monitor runtime, check for error codes, and receive descaling reminders from your phone. The 15-year heat exchanger warranty is 3 years longer than any Rinnai or Noritz model.
Installation notes: Two 2" PVC vent pipes (intake and exhaust). Max concentric vent run: 60 feet. Minimum 3/4" gas line. 120V/3A outlet for controls. Available in both indoor (NPE-2 240S) and outdoor models.
Real-world example: A family of 5 in Portland, OR (groundwater 48°F, 72°F rise needed) replaced a 50-gallon tank. The NPE-2 240S delivers 5.4 GPM — enough for two showers and a kitchen faucet simultaneously. Annual gas bill dropped from $410 to $275. Payback on the $3,800 install: 8.2 years, or 5.6 years after the IRA credit.
#2: Noritz EZ111 — Best Efficiency
Why it's #2: The 0.97 UEF is the highest AHRI-certified efficiency in the residential gas tankless category.
Noritz's EZ series uses a unique fire-tube heat exchanger design that maximizes the surface area between combustion gases and water, extracting more heat per BTU than competing designs. The 11:1 turndown ratio (18,000–199,900 BTU/h) means the unit can modulate down to very low output for single-faucet use, virtually eliminating the cold-water sandwich effect.
The EZLink Wi-Fi module provides remote monitoring and diagnostics similar to Navien's NaviLink. The unit supports optional external recirculation (not built-in like Navien).
Installation notes: PVC/CPVC venting up to 65 feet. Compatible with concentric and separate vent configurations. Requires condensate neutralizer in most jurisdictions.
Real-world example: A couple in Denver, CO (5,280 ft elevation, 45°F groundwater) installed the EZ111 with the altitude derate kit. Effective output: ~175,000 BTU/h at altitude. Delivers 4.2 GPM at 75°F rise — enough for their 2-bathroom home. The 0.97 UEF saves $65/year vs a 0.93 UEF unit, paying for the Noritz premium in 5 years.
#3: Rinnai RU199iN — Best Reliability
Why it's #3: The most field-proven platform with the largest service network in North America.
Rinnai has been selling tankless heaters in the U.S. since 1991. Their RU series benefits from decades of design iteration. The RU199iN isn't the most efficient (0.93 UEF) or the cheapest, but Rinnai's first-call resolution rate and parts availability are industry-leading.
The ThermaCirc360 recirculation system is available as an add-on. Scale detection alerts notify you before mineral buildup causes problems. Available in both indoor and outdoor variants (RU199eN for outdoor). Propane version: RU199iP.
Installation notes: Rinnai offers both concentric and twin-pipe venting options. Max vent run: 60 feet concentric. Their mobile app walks installers through commissioning, reducing installation errors.
Real-world example: A contractor in Atlanta, GA installed the RU199iN for a family of 6 with a 3,200 sq ft home. Groundwater at 62°F means only a 58°F rise — the unit delivers 7.2 GPM at that rise, handling three showers plus a dishwasher with room to spare. Five years in, zero service calls beyond annual descaling.
#4–#6: The Mid-Range Condensing Tier
Navien NPE-2 180S ($1,400–$1,700): The same technology as the 240S at a lower output. At 180,000 BTU/h and 4.8 GPM at 77°F rise, it's correctly sized for 2–3 bathroom homes in moderate climates. Same 15-year warranty and built-in recirculation. The smart buy when you don't need 199,900 BTU.
Rinnai RU160iN ($1,400–$1,650): Rinnai's mid-output condensing unit at 160,000 BTU/h. Delivers 4.2 GPM at 77°F rise. Ideal for warm-climate whole-home use or as a primary unit paired with a point-of-use electric at a distant bathroom.
Rheem RTGH-RH10 ($1,500–$1,800): Rheem's condensing entry with built-in recirculation. The 0.93 UEF matches Rinnai, and the Home Depot/Lowe's distribution makes it the easiest condensing unit to source. The 12-year heat exchanger warranty is standard for the category.
#7–#10: The Non-Condensing Value Tier
Non-condensing units make sense in two scenarios: replacing an existing non-condensing unit (stainless venting already installed) or when budget is the primary constraint.
Rinnai V94iN ($1,000–$1,250): The best non-condensing unit, period. At 199,000 BTU and 4.5 GPM at 77°F rise, it matches some condensing units on throughput. The 0.82 UEF is typical for non-condensing. Proven platform, 12-year warranty.
Rheem RTG-84XLN ($900–$1,100): Rheem's workhorse. 180,000 BTU, 4.0 GPM at 77°F rise. Hot-start programming reduces cold-water sandwich. Available everywhere, easy to service.
Noritz NRC83 ($800–$1,000): The lowest-cost name-brand unit that still delivers solid whole-home performance in warm climates. 157,000 BTU limits cold-climate use.
Rinnai V75iN ($750–$950): Entry-level Rinnai at 180,000 BTU. Shorter 10-year warranty. Best for budget installs in warm climates.
Non-condensing trade-off: The $400–$800 saved on the unit is partially offset by $200–$500 more expensive stainless steel venting AND the loss of the IRA tax credit (requires UEF ≥ 0.95). A condensing Navien NPE-2 180S at $1,500 with a $450 tax credit nets to $1,050 — barely more than a non-condensing V94iN at $1,125 with no credit.
Gas Tankless Sizing Guide
BTU Sizing Formula
BTU/h = GPM × ΔT × 500 ÷ Efficiency
Where GPM = peak simultaneous demand, ΔT = temperature rise (desired output minus incoming water temp), and 500 = constant (BTU to heat 1 gallon 1°F per hour).
Values exceeding 199,900 BTU/h require multiple units in parallel.
Parallel Installation
For homes needing more than 5.5 GPM at high temperature rises, two units in parallel are the standard solution. Each unit handles a portion of the demand, with a manifold distributing flow. Installation adds $1,000–$2,000 for the second unit's venting and gas piping, plus the cost of the unit itself.
Parallel tip: Use identical units from the same manufacturer. Navien and Rinnai both offer cascade control kits ($100–$200) that automatically balance the load between units and alternate which fires first, equalizing wear.
Propane-Specific Considerations
Propane Tank Sizing
A 199,900 BTU/h tankless unit draws approximately 2.18 gallons of propane per hour at full fire. Your propane tank needs to deliver adequate vapor pressure to sustain this draw:
May work in warm weather but fails in cold weather when vapor pressure drops.
Critical: A propane tank that's too small can't deliver enough vaporized gas, causing the water heater to shut down on error codes — especially in winter. Many tankless failures blamed on the unit are actually undersized propane tank problems. Work with your propane supplier to confirm tank capacity.
LP Conversion
Some gas tankless models sell only as natural gas, with a separate LP conversion kit available. Others sell separate NG and LP SKUs with factory-calibrated orifices. Using the factory LP model is always preferred over a field conversion kit — the orifice sizing is more precise, and there's no risk of installer error.
Real-World Gas Tankless Examples
Example 1: Rural Propane Home — South Carolina
Setup: 2,000 sq ft farmhouse, 2 bathrooms, 500-gallon propane tank. Groundwater: 62°F. Peak demand: 4.0 GPM.
Unit: Rinnai RU160iP (propane, condensing, 160,000 BTU/h). Delivers 5.2 GPM at 58°F rise — 30% headroom above peak demand.
Result: Annual propane use for hot water dropped from 350 gallons (old tank) to 220 gallons. At $2.80/gallon, that's $364/year savings. Total install: $3,200. Payback: 8.8 years.
Example 2: New Build — Suburban Dallas
Setup: 3,500 sq ft, 4 bathrooms, natural gas. Groundwater: 65°F. Peak demand: 6.5 GPM.
Unit: Navien NPE-2 240S. Delivers 6.8 GPM at 55°F rise — tight but adequate. Installed during construction (easier gas/vent routing).
Result: Annual gas cost: $215. Comparable tank would cost: $350/year. Install cost (new construction discount): $2,800. Payback: 5.9 years. IRA credit: $480.
Example 3: Cold-Climate Upgrade — Buffalo, NY
Setup: 2,800 sq ft, 3 bathrooms, family of 5. Groundwater: 42°F. Peak demand: 7.0 GPM.
Unit: Two Rinnai RU199iN units in parallel with cascade control. Combined output: ~10 GPM at 78°F rise.
Result: Total install: $7,200. Annual gas savings vs 75-gallon tank: $280. Unlimited hot water for the first time — the family previously ran cold during morning shower routines. Payback is long (15+ years on energy alone), but the comfort upgrade was the primary motivator.
Key Takeaways
- Best overall gas tankless: Navien NPE-2 240S (0.96 UEF, 5.4 GPM at 77°F rise, 15-year warranty)
- Best efficiency: Noritz EZ111 (0.97 UEF — highest AHRI-certified)
- Best reliability: Rinnai RU199iN/iP (longest track record, largest service network)
- Best value: Rinnai V94iN (non-condensing, $1,000–$1,250, 4.5 GPM at 77°F rise)
- Condensing vs non-condensing: Condensing saves $50–$200/year and qualifies for IRA tax credits — usually worth the $400–$800 premium
- Propane users: Verify your tank can sustain 200K+ BTU/h draw in cold weather
- Cold climates (ΔT > 70°F): Budget for a premium condensing unit or parallel setup
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