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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

T-H3J-OS-N-1

Takagi / 4.7 GPM Condensing Tankless Water Heater
Endless hot water, but gas-line capacity and venting decide the install.
ShortlistRunning costInstall changeFull specs
UEF0.95Certified efficiency
Max flow4.7 GPMWhole-home demand signal
Footprint22.5" × 10.75"Height × depth
Running cost~$242/yrU.S. average natural gas
Estimated annual savings: $141 compared to a standard standard gas tank. Based on U.S. average energy prices. See all condensing tankless models

T-H3J-OS-N-1 operating cost

This unit saves roughly $141 every year compared to the standard gas tank it replaces
T-H3J-OS-N-1
$242/yr
Std tank (0.6 UEF)
$383/yr
~4.6year payback
At $141/yr in savings, the upfront premium pays for itself in about 4.6 years. Over 10 years: roughly $760 in net savings.
Your state changes the math. Annual cost ranges from ~$117/yr (ID) to ~$888/yr (HI).
U.S. avg natural gas: $1.36/therm (EIA, Dec 2025).
T-H3J-OS-N-1 in the condensing tankless class: #3 of 4 on efficiency.

Should this be on your shortlist?

Not ideal for

lower efficiency than most class peers, lowest flow rate in class

  • Why it makes shortlists: solid mid-class efficiency (#3 of 4)
Shortlist alternatives in condensing tankless:
Navien NPE-210S2UEF 0.96 · 5.3 GPMNavien NPE-240S2UEF 0.96 · 5.8 GPMRheem RTGH-95DVLN-3UEF 0.93 · 9.5 GPM
Check price and availability: Takagi T-H3J-OS-N-1 on Amazon
The bill may work. Now check what actually changes on install day before you let the shortlist settle.

Switching to the T-H3J-OS-N-1

From a gas tank

✓
Uses existing gas line, but may need upsized gas supply for 160,000 BTU input.
▲
New venting required. Power 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. Power 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.

T-H3J-OS-N-1 installation specifications

Dimensions

Height22.5 in
Width17.75 in
Depth10.75 in
Weight58 lbs
Connections3/4 inch NPT

Electrical

Voltage120V
Amperage5A

Venting

TypePower Vent
MaterialCategory Iv Pvc Cpvc
CategoryIV

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
#3Top TierEfficiency · 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
#4of 4Flow Rate
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 Takagi T-H3J-OS-N-1

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

How much does the T-H3J-OS-N-1 cost to run per year?
~$242/yr at the U.S. average natural gas rate. That is roughly $141/yr less than a standard gas tank.
How many fixtures can the T-H3J-OS-N-1 run at once?
4.7 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 T-H3J-OS-N-1 fit in my space?
22.5" tall, 17.75" wide, 10.75" deep. Measure your space including clearances before ordering.
What gas connection does the T-H3J-OS-N-1 need?
160,000 BTU input. Verify your gas line can supply this flow rate. Most homes with existing gas water heaters have adequate supply.
What warranty does the T-H3J-OS-N-1 come with?
15-year heat exchanger warranty, 5-year parts.
Is the T-H3J-OS-N-1 ENERGY STAR certified?
Yes. ENERGY STAR certified condensing tankless. May qualify for utility rebates in your area.
Full specifications
Performance
UEF0.95
Max Flow Rate4.7 GPM
Min Activation Flow1 GPM
BTU Input160,000 BTU/hr
Draw PatternHigh
Est. Annual Energy178 therms/yr
Physical
Height22.5 in
Width17.75 in
Depth10.75 in
Weight58 lbs
Connections3/4 inch NPT
Electrical
Voltage120 V
Amperage5 A
Venting
TypePower Vent
MaterialCategory Iv Pvc Cpvc
Warranty
Heat Exchanger15 yr
Parts5 yr
Certifications
ENERGY STARCertified
MarketsUnited States, Canada
Keep the route moving

Jump to the type guide or brand page to see other options.

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