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Heat Pump Water HeatersHigh-efficiency electric replacements and hybrid tanks.Condensing Tankless Water HeatersCondensing whole-home flow with venting constraints.Gas Tank Water HeatersStraight swaps when gas storage is still the fit.

Plan Your Swap

Sizing guideCapacity, first-hour rating, and temperature-rise fit.Accessories hubInstall extras, code-adjacent parts, and paid-link accessory picks.Upgrade from NHP50Replacement candidates and projected operating-cost delta.Upgrade from NHP65Replacement candidates and projected operating-cost delta.Upgrade from NHP80Replacement candidates and projected operating-cost delta.Upgrade from NPE 210S2Replacement candidates and projected operating-cost delta.Upgrade from PROE50 T2 RH95Replacement candidates and projected operating-cost delta.HPTA 50 2 vs HPTA 80 2Side-by-side specs, efficiency, and fit differences.HPTS 50 2 vs NHP50Side-by-side specs, efficiency, and fit differences.NHP120 vs PROPH80 T2 RH400 30Side-by-side specs, efficiency, and fit differences.NPE 210S2 vs NPE 240S2Side-by-side specs, efficiency, and fit differences.

Guides & Data

California heat pump guideLocal rates, rebates, and operating costs.Colorado heat pump guideLocal rates, rebates, and operating costs.Massachusetts heat pump guideLocal rates, rebates, and operating costs.Oregon heat pump guideLocal rates, rebates, and operating costs.Washington heat pump guideLocal rates, rebates, and operating costs.DOE 2029 standardsWhat changes in 2029 and which product classes move first.

Brands

A.O. Smith Water HeatersPublished models, product lines, and brand coverage.Bradford White Water HeatersPublished models, product lines, and brand coverage.Navien Water HeatersPublished models, product lines, and brand coverage.Noritz Water HeatersPublished models, product lines, and brand coverage.Rheem Water HeatersPublished models, product lines, and brand coverage.Rinnai Water HeatersPublished models, product lines, and brand coverage.Takagi Water HeatersPublished models, product lines, and brand coverage.
Model specs

NPE-240S2

Navien / 5.8 GPM Condensing Tankless Water Heater
Endless hot water, but gas-line capacity and venting decide the install.
ShortlistRunning costInstall changeFull specs
UEF0.96Certified efficiency
Max flow5.8 GPMWhole-home demand signal
Footprint27.4" × 13.2"Height × depth
Running cost~$239/yrU.S. average natural gas
Estimated annual savings: $144 compared to a standard standard gas tank. Based on U.S. average energy prices. See all condensing tankless models

NPE-240S2 operating cost

This unit saves roughly $144 every year compared to the standard gas tank it replaces
NPE-240S2
$239/yr
Std tank (0.6 UEF)
$383/yr
~4.5year payback
At $144/yr in savings, the upfront premium pays for itself in about 4.5 years. Over 10 years: roughly $790 in net savings.
Your state changes the math. Annual cost ranges from ~$116/yr (ID) to ~$878/yr (HI).
U.S. avg natural gas: $1.36/therm (EIA, Dec 2025).
NPE-240S2 in the condensing tankless class: #2 of 4 on efficiency.

Should this be on your shortlist?

Best for

top-tier efficiency

  • Why it makes shortlists: top-half efficiency in a 4-model class
Shortlist alternatives in condensing tankless:
Navien NPE-210S2UEF 0.96 · 5.3 GPMTakagi T-H3J-OS-N-1UEF 0.95 · 4.7 GPMRheem RTGH-95DVLN-3UEF 0.93 · 9.5 GPM
The bill may work. Now check what actually changes on install day before you let the shortlist settle.

Switching to the NPE-240S2

From a gas tank

✓
Uses existing gas line, but may need upsized gas supply for 199,000 BTU input.
▲
New venting required. Direct Vent uses different venting than a standard tank.
▲
Condensate drain needed for condensing units.
✓
Wall-mounted. Frees floor space where your old tank stood.
Plumber handles most of the work. Gas line sizing is the key question.

From another tankless

✓
Same wall mount location. Same gas and water connections.
▲
Check venting compatibility. Vent diameter and termination may differ.
✓
Electrical outlet likely already in place.
Simplest path if venting and gas line sizing are compatible. Verify before ordering.

From an electric tank

▲
Gas line required. Major install if no existing gas supply.
▲
New venting required. Direct Vent through exterior wall or roof.
✓
No more waiting for a tank to refill. Endless hot water on demand.
Biggest install scope. Needs plumber + possibly gas line work.
Gas line sizing and venting matter more than flow rate. The headline GPM only works if the gas supply and vent run support it.

NPE-240S2 installation specifications

Dimensions

Height27.4 in
Width17.3 in
Depth13.2 in
Weight73 lbs
Connections3/4 inch NPT

Electrical

Voltage120V
Amperage5A
Breaker15A dedicated

Venting

TypeDirect Vent
MaterialCategory Iv Pvc Cpvc
CategoryIV
Vent size2 in

Common install considerations for gas tankless units

What is required depends on your existing installation, local code, and installer preference.

Condensate Neutralizer Kit Commonly required Check on Amazon (paid link)
Gas Flex Connector Commonly required Check on Amazon (paid link)
Venting Kit Commonly required Check on Amazon (paid link)
Full accessories list

Warranty

Coverage

Heat exchanger15 yr
Parts5 yr
Class rankings: condensing tankless water heaters

Rankings

Efficiency (UEF) higher is better
#1Class LeaderEfficiency · 4 models tested
1
Navien NPE-210S2
0.96
2
Navien NPE-240S2
0.96
3
Takagi T-H3J-OS-N-1
0.95
4
Rheem RTGH-95DVLN-3
0.93
Max Flow Rate higher is better
#2Runner-UpFlow Rate · 4 models tested
1
Rheem RTGH-95DVLN-3
9.5 GPM
2
Navien NPE-240S2
5.8 GPM
3
Navien NPE-210S2
5.3 GPM
4
Takagi T-H3J-OS-N-1
4.7 GPM

Common questions about the Navien NPE-240S2

From manufacturer specs, EIA energy data, and DOE regulations.

How much does the NPE-240S2 cost to run per year?
~$239/yr at the U.S. average natural gas rate. That is roughly $144/yr less than a standard gas tank.
How many fixtures can the NPE-240S2 run at once?
5.8 GPM maximum. At typical fixture flow rates (2 GPM shower, 1.5 GPM faucet), that handles 2 to 3 simultaneous fixtures. Minimum activation flow: 1 GPM.
Will the NPE-240S2 fit in my space?
27.4" tall, 17.3" wide, 13.2" deep. Measure your space including clearances before ordering.
What electrical circuit does the NPE-240S2 need?
120V, 15A dedicated circuit. Check your electrical panel before installation.
What warranty does the NPE-240S2 come with?
15-year heat exchanger warranty, 5-year parts.
Is the NPE-240S2 ENERGY STAR certified?
Yes. ENERGY STAR certified condensing tankless. May qualify for utility rebates in your area.
Full specifications
Performance
UEF0.96
Max Flow Rate5.8 GPM
Min Activation Flow1 GPM
BTU Input199,000 BTU/hr
Draw PatternHigh
Est. Annual Energy176 therms/yr
Physical
Height27.4 in
Width17.3 in
Depth13.2 in
Weight73 lbs
Connections3/4 inch NPT
Electrical
Voltage120 V
Amperage5 A
Breaker15A dedicated
Venting
TypeDirect Vent
MaterialCategory Iv Pvc Cpvc
Vent Size2 in
Warranty
Heat Exchanger15 yr
Parts5 yr
Certifications
ENERGY STARCertified
MarketsUnited States, Canada
Keep the route moving

Other Navien models and the full condensing tankless guide, if this one isn't the right fit.

Head-to-head comparisons
Condensing Tankless guideAll Navien modelsSizing guideInstallation accessoriesAll models
Sources. ENERGY STAR, Navien, Retailer listing. Data compiled March 2026.Methodology
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