Condensing Gas Tankless Water Heaters
What to know
Households with natural gas service that want continuous hot water and long-term energy savings. Works well for homes with moderate to high usage patterns, especially where space is limited. Good fit for new construction where gas line and venting can be planned into the design.
Homes without existing gas service due to the cost of running a gas line. Very high simultaneous demand homes (multiple showers plus appliances at once) unless multiple units or a recirculation system are installed. Not cost-effective for low-usage households where payback is too slow.
Advantages
- Endless hot water supply since it heats on demand rather than storing a fixed volume
- 90-98% thermal efficiency, 15-20% more efficient than non-condensing tankless units
- Compact wall-mount design saves floor space compared to tank water heaters
- Expected lifespan of 20+ years with proper maintenance, longer than tank-style heaters
- Can use PVC or CPVC for venting instead of expensive stainless steel, reducing installation costs
Trade-offs
- Higher upfront equipment cost ($1,000-$2,500) than tank water heaters
- Flow rate is limited, typically 5-11 GPM; simultaneous high-demand fixtures can exceed capacity
- Requires periodic descaling of the heat exchanger, especially in hard water areas
- Brief delay (cold water sandwich effect) when hot water use stops and restarts quickly
- Minimum flow rate of 0.4-0.6 GPM required to activate the burner, which may not serve low-flow fixtures
Is this the right type?
Fastest way to narrow this category
All Models
| Model | Brand | UEF | Max GPM* | BTU Input | Est. Cost/yr |
|---|---|---|---|---|---|
| NPE-210S2 | Navien | 0.96 | 5.3 | 180,000 | ~$239 |
| NPE-240S2 | Navien | 0.96 | 5.8 | 199,000 | ~$239 |
| T-H3J-OS-N-1 | Takagi | 0.95 | 4.7 | 160,000 | ~$242 |
| RTGH-95DVLN-3 | Rheem | 0.93 | 9.5 | 199,900 | ~$250 |
● Best in group
*Max GPM is rated at a specific temperature rise (typically 35°F). Actual delivery drops significantly with higher temperature rise. A unit rated 8 GPM at 35°F rise may deliver only 5 GPM at 77°F rise in cold climates. Always check the manufacturer's GPM-at-temperature-rise chart.
Installation requirements
What installation involves
Electrical: Requires a standard 120V outlet for the electronic controls and fan. Some units draw up to 150W during operation. Venting: Condensing models can vent with Schedule 40 PVC, CPVC, or polypropylene. Horizontal or vertical venting supported. Maximum vent run varies by model, typically 40-100 feet equivalent. Space: Wall-mounted unit roughly 27 x 18 x 10 inches. Requires clearances per manufacturer specs, typically 12 inches on sides and 36 inches in front for service access. Other: Adequate gas line sizing is critical. Many homes need a 3/4-inch gas line upgrade. Condensate drain required, condensate is mildly acidic (pH 3-4) and may require a neutralizer per local code. In hard water areas, a water softener or scale inhibitor is recommended.
Equipment typically costs $1,000 - $2,500. Installed cost including labor and materials: $2,500 - $5,000.
- Sizing guide Find the right capacity
- Replacement cost guide Equipment, labor, and hidden costs
- Heat pump vs gas tankless Comparing technologies across fuel types