Product images: Amazon listings
Written from the listing's specs, not from our own use · How we rate
We like the Takagi T-H3S-OS-N Condensing Outdoor for the mix: an 8 GPM maximum flow, condensing efficiency and outdoor mounting that skips the flue. It is a good match for a two-bathroom house with one shower running at a time, at 6.4/10 on its documented specs.
| Brand | Takagi |
|---|---|
| Category | Gas tankless water heaters |
| Fuel | Natural gas |
| Stated mounting location | Outdoor |
| Stated maximum flow | 8 GPM |
| Condensing design | Stated in the listing title |
| ASIN | B00DDPZ5JA |
Full listing title: Takagi T-H3S-OS-N Condensing High Efficiency Natural Gas Outdoor Tankless Water Heater, 8-Gallon Per Minute
| Fuel | Natural GasFull listing title |
|---|---|
| Stated mounting location | OutdoorFull listing title |
| Stated maximum flow | 8-Gallon Per MinuteFull listing title |
| Condensing design | CondensingFull listing title |
Two gas tankless heaters on natural gas too, with about the same flow, closest to it on our rating, each with a dated price.
That's the maximum flow the listing states, and headline flows are usually quoted at a mild temperature rise. With January water coming in at 42 °F and a 105 °F shower, the rise is 63 °F and the real flow is lower; the maker's flow chart has that number. At 2 GPM a shower (our calculator's figure), the headline means two showers and a kitchen tap, less when the water comes in cold.
What it has going for it
Condensing. A second heat exchanger pulls heat out of the exhaust before it leaves, so more of the gas you pay for ends up in the water. The exhaust runs cool enough for plastic vent pipe, and the condensate needs a drain.
Mounts outside. No vent pipe through the roof or the rim joist: it hangs on an outside wall and breathes on its own. In a cold climate, ask what keeps it from freezing.
Mild winters: an outside wall is the easy spot. No vent through the roof or the rim joist, no combustion air to plan inside the house.
Hard freezes: the listing names no freeze protection, so ask the seller what keeps it from bursting before it goes on a north wall.
What the Takagi T-H3S-OS-N Condensing Outdoor listing names:
Read the installation manual for the vent, the gas line size and the clearances before you order; it overrides anything above.
At the price on Sep 30, 2026, each GPM of stated maximum flow works out at about $169.49 (price ÷ stated GPM, our arithmetic). That puts it in the pricier third of the 32 outdoor tankless heaters we have a price and a stated flow for.
Outside mounting saves the vent pipe; the gas line, the water lines and a weatherproof outlet are still a separate bill.
The button opens the exact listing (ASIN B00DDPZ5JA), where today's price, stock and seller apply.
Two showers and the dishwasher at once? The A. O. Smith 10 GPM Natural Gas Outdoor (8.0/10) states up to 10 GPM.
Hard freezes where you live? The Ranein 190,000 BTU Natural Gas Indoor (7.9/10) is an indoor unit, out of the frost.
On propane, not natural gas? The APUS 190,000 BTU Propane Outdoor (6.9/10) runs on propane.
Our take
Our favourite thing about the Takagi T-H3S-OS-N Condensing Outdoor is an 8 GPM maximum flow, closely followed by condensing efficiency. No buyer reviews yet, so the Takagi T-H3S-OS-N Condensing Outdoor has to win you over on paper. The catch with this Takagi outdoor tankless heater: no stated temperature hold, while most picks here claim ±1 °F. We'd pick it if you run one shower and the kitchen tap at once, rarely more; otherwise, put it next to the Rheem RTG 7.0 GPM Propane Outdoor first.
It goes on an outside wall, with gas, water and power run to it. a licensed pro handles it, and often a permit.
Hot water arrives after the cold already in the pipes, then stays. A trickle from a bathroom tap may not light the burner; open it a bit more.
January water comes in colder, so the same unit gives fewer GPM. Stagger the showers if you sized it tight.
Flush the heat exchanger with a pump and a descaler (the service valves make it an hour's job), check the condensate drain and the neutralizer, and clear leaves and wasp nests from the cabinet vents. Our flushing and descaling guide has the checklist.
Before the Takagi T-H3S-OS-N Condensing Outdoor goes in your cart, check your winter flow: 8 GPM is a best case, so run your January numbers in our calculator first.
Count the fixtures that run together on a busy morning (our calculator uses 2 GPM a shower, 1.5 for the kitchen), then compare with the maker's chart. Our sizing guide shows how.
Pick a wall away from windows and doors, with power for the controls. Our indoor vs outdoor guide compares the two installs.
A condensing unit drips acidic water that needs a drain, often through a neutralizer. Our condensing guide explains the extra parts.
Hard water scales the heat exchanger. Service valves on the water lines turn the yearly flush into an hour with a bucket and a pump; our flushing and descaling guide shows the routine.
How the Takagi T-H3S-OS-N Condensing Outdoor stacks up against the closest alternative, the Rheem RTG 7.0 GPM Propane Outdoor.
| Criterion | Takagi T-H3S-OS-N Condensing Outdoor | Rheem RTG 7.0 GPM Propane Outdoor |
|---|---|---|
| Our rating | 6.4/10 | 6.7/10 |
| Max flow | 8 GPM | 7 GPM |
| Gas input | Not stated | 160,000 BTU/h |
| Efficiency | Condensing | Not stated |
| Temperature hold | Not stated | ±1 °F stated |
| Buyer reviews | None captured | 55 · 4.2/5 |
Pick the Rheem RTG 7.0 GPM Propane Outdoor if you want our higher-rated option (6.7/10), with a bigger burner (160,000 BTU/h) and a stated ±1 °F hold; stay with the Takagi T-H3S-OS-N Condensing Outdoor for more flow (8 GPM) and a condensing design.
We rate it 6.4/10 (fair). The rating comes from its documented listing alone, as no customer-review record is captured yet.
The listing states a maximum flow of 8 GPM. The headline flow is a mild-weather number: with cold winter water coming in, the same unit gives you less. Read the maker's flow chart at your winter rise, or let our flow-rate calculator do the sums.
The listing says outdoor mounting. It only goes inside if the maker lists that exact model for indoor use, with the venting it specifies; a licensed gas installer confirms the spot under your local code.
Its listing states up to 8 GPM, a condensing heat exchanger and outdoor mounting that skips the flue. These are the seller's figures, not our measurements: how steady the temperature is in your shower and how it copes with your winter water can't be read from a listing.
Your winter flow: count the fixtures that run together on a busy morning (our calculator uses 2 GPM a shower, 1.5 for the kitchen), then compare with the maker's chart. Our sizing guide shows how. The outside wall: pick a wall away from windows and doors, with power for the controls. Our indoor vs outdoor guide compares the two installs. The condensate: a condensing unit drips acidic water that needs a drain, often through a neutralizer. Our condensing guide explains the extra parts. Flushing: hard water scales the heat exchanger. Service valves on the water lines turn the yearly flush into an hour with a bucket and a pump; our flushing and descaling guide shows the routine.
We link to the exact listing on Amazon, where today's price, stock and seller apply. It is an affiliate link, and it has no effect on the rating.
No, we haven't used it ourselves. Everything on this page comes from its listing, read line by line and weighed with our published formula.