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.
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, Jan 2026).
Your state changes the cost. Ranges from $117/yr to $888/yr depending on your state's natural gas rate.
T-H3J-OS-N-1 cost by state
Ranges from $117/yr to $888/yr depending on your state's natural gas rate. U.S. average: $242/yr.
Alabama$292/yr$1.64/therm
Alaska$219/yr$1.23/therm
Arizona$308/yr$1.73/therm
Arkansas$338/yr$1.90/therm
California$408/yr$2.29/therm
Colorado$178/yr$1.00/therm
Connecticut$278/yr$1.56/therm
Delaware$294/yr$1.65/therm
District of Columbia$262/yr$1.47/therm
Florida$406/yr$2.28/therm
Georgia$285/yr$1.60/therm
Hawaii$888/yr$4.99/therm
Idaho$117/yr$0.66/therm
Illinois$162/yr$0.91/therm
Indiana$176/yr$0.99/therm
Iowa$151/yr$0.85/therm
Kansas$215/yr$1.21/therm
Kentucky$215/yr$1.21/therm
Louisiana$285/yr$1.60/therm
Maryland$272/yr$1.53/therm
Massachusetts$441/yr$2.48/therm
Michigan$176/yr$0.99/therm
Minnesota$162/yr$0.91/therm
Mississippi$249/yr$1.40/therm
Missouri$251/yr$1.41/therm
Montana$151/yr$0.85/therm
Nebraska$176/yr$0.99/therm
Nevada$171/yr$0.96/therm
New Hampshire$329/yr$1.85/therm
New Jersey$247/yr$1.39/therm
New Mexico$190/yr$1.07/therm
New York$276/yr$1.55/therm
North Carolina$306/yr$1.72/therm
North Dakota$146/yr$0.82/therm
Ohio$192/yr$1.08/therm
Oklahoma$190/yr$1.07/therm
Oregon$303/yr$1.70/therm
Pennsylvania$239/yr$1.34/therm
Rhode Island$418/yr$2.35/therm
South Carolina$281/yr$1.58/therm
South Dakota$151/yr$0.85/therm
Tennessee$194/yr$1.09/therm
Texas$331/yr$1.86/therm
Utah$185/yr$1.04/therm
Vermont$287/yr$1.61/therm
Virginia$265/yr$1.49/therm
Washington$267/yr$1.50/therm
West Virginia$214/yr$1.20/therm
Wisconsin$189/yr$1.06/therm
Wyoming$187/yr$1.05/therm
Based on 178.0 therm/yr (ENERGY STAR rated) at each state's residential natural gas rate (EIA, Jan 2026).
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 GPMCheck price and availability: Takagi T-H3J-OS-N-1 on Amazon (paid link)
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
Safety and installation warnings
These warnings apply to this water heater type. Always follow the manufacturer's installation instructions and local building codes. Hire a licensed professional for installation.
Carbon monoxide hazard. Gas water heaters produce combustion byproducts including carbon monoxide (CO). Proper venting is essential. Never operate a gas water heater with damaged, disconnected, or blocked venting. Install a CO detector near the unit. If you smell gas or suspect a CO leak, leave the building and call your gas utility.
Garage installation. Gas water heaters installed in garages must have the ignition source at least 18 inches above the floor (IRC G2408.2) to prevent ignition of gasoline vapors. An elevated platform or wall-mount is required.
Fuel type match. Natural gas and propane (LP) models use different orifice sizes. Using the wrong fuel type causes incomplete combustion and carbon monoxide production. Verify the unit matches your fuel supply before installation. Conversion kits are available for some models but must be installed by a qualified technician.
Combustion air supply. Gas water heaters require adequate combustion air per local code (IRC/IMC). A unit in a confined space (closet, utility room) without proper air supply can backdraft, producing carbon monoxide. Ensure the installation space meets combustion air requirements for the unit's BTU input.
Scald prevention. The recommended maximum water temperature is 120°F to prevent scalding. Higher temperatures (130-140°F) reduce Legionella bacteria risk but require a thermostatic mixing valve at the outlet to deliver safe temperatures at fixtures. Some jurisdictions require mixing valves when the tank is set above 120°F.
Common install considerations for gas tankless units
What is required depends on your existing installation, local code, and installer preference.
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
2
Navien NPE-240S2
3
Takagi T-H3J-OS-N-1
4
Rheem RTGH-95DVLN-3
Max Flow Rate higher is better
#4of 4Flow Rate
1
Rheem RTGH-95DVLN-3
2
Navien NPE-240S2
3
Navien NPE-210S2
4
Takagi T-H3J-OS-N-1
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 | |
| UEF | 0.95 |
|---|---|
| Max Flow Rate | 4.7 GPM |
| Min Activation Flow | 1 GPM |
| BTU Input | 160,000 BTU/hr |
| Draw Pattern | High |
| Est. Annual Energy | 178 therms/yr |
| Physical | |
| Height | 22.5 in |
| Width | 17.75 in |
| Depth | 10.75 in |
| Weight | 58 lbs |
| Connections | 3/4 inch NPT |
| Electrical | |
| Voltage | 120 V |
| Amperage | 5 A |
| Venting | |
| Type | Power Vent |
| Material | Category Iv Pvc Cpvc |
| Warranty | |
| Heat Exchanger | 15 yr |
| Parts | 5 yr |
| Certifications | |
| ENERGY STAR | Certified |
| Markets | United States, Canada |
Keep the route moving
Jump to the type guide or brand page to see other options.
Sources. ENERGY STAR, Retailer listing, Takagi. Specs last verified 2026-03-17.Methodology
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