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Written from the listing and 91 buyer reviews, not from our own use · How we rate
The Rinnai RUCS75iN Natural Gas is an indoor gas tankless heater built around a 7.5 GPM maximum flow. It suits a two-bathroom house with one shower running at a time, at 6.6/10 on our rating.
| Brand | Rinnai |
|---|---|
| Category | Gas tankless water heaters |
| Fuel | Natural gas |
| Stated mounting location | Indoor |
| Stated maximum flow | 7.5 GPM |
| Stated warranty | 1 years |
| Buyer reviews | 91 · 4.4/5 |
| ASIN | B010Q1XG7G |
Full listing title: Rinnai RUCS75iN Tankless Hot Water Heater, Natural Gas
| Fuel | Natural GasFull listing title |
|---|---|
| Stated mounting location | RUCS75iNFull listing title (Rinnai model suffix: i = indoor, e = exterior) |
| Stated maximum flow | up to 7.5 GPMListing text |
Not in our top-5 rankings
What it's made for: a two-bathroom house with one shower running at a time.
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. Counting 2 GPM per shower, as our calculator does, that's two showers and a kitchen tap, less when the water comes in cold.
One at a time, plus the kitchen tap: 7.5 GPM covers that on paper.
Two at once: possible where the tap water comes in warm. In a northern January the second shower is the one that runs lukewarm, so read the flow chart at a 63 °F rise first.
What the Rinnai RUCS75iN Natural Gas listing names:
Warranty & support: 1-year warranty, as stated in the listing.
That is the maker's promise, not ours. Keep the invoice, register the Rinnai RUCS75iN Natural Gas if the maker asks, and read the install conditions: many tankless warranties need a licensed install and regular flushing.
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 $118.97 (price ÷ stated GPM, our arithmetic). That puts it around the middle of the 45 indoor gas tankless heaters we have a price and a stated flow for.
Count the install in the budget: vent pipe, possibly a 3/4" gas line, and a licensed plumber or gas fitter.
The button opens the exact listing (ASIN B010Q1XG7G), where today's price, stock and seller apply.
Two showers and the dishwasher at once? The MIZUDO 199,000 BTU Natural Gas Indoor (9.2/10) states up to 10.3 GPM.
No easy route for a vent pipe? The Rheem RTG 8.4 GPM Natural Gas Outdoor (7.7/10) mounts on an outside wall, per its listing.
Want the high-efficiency kind? The Rheem RTGH 8.4 GPM Natural Gas Indoor (7.3/10) is a condensing unit, per its listing.
Our take
The Rinnai RUCS75iN Natural Gas is about a 7.5 GPM maximum flow, and it doesn't pretend to be more. Only 91 buyers have rated it so far (4.4/5), so treat the score as an early read. The catch with the Rinnai RUCS75iN Natural Gas: 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 APUS 140,000 BTU Natural Gas Indoor first.
Old tank out, unit on the wall, vent through the wall or the roof. 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), and clean the inlet filter. Our flushing and descaling guide has the checklist.
Buyers give it 4.4/5, a strong record, above our ranked picks' 4.3 average. 91 reviews is still a modest pile, so a handful of new ones can move it.
Before the Rinnai RUCS75iN Natural Gas goes in your cart, check your winter flow: 7.5 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.
A licensed plumber or gas fitter confirms the vent route, the combustion air and a gas line that can deliver its full input. Get that quote before you order; our installation guide lists what they will ask.
1 years are stated. Read what it requires: a licensed install, the gas type and regular flushing are the usual conditions.
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 Rinnai RUCS75iN Natural Gas stacks up against the closest alternative, the APUS 140,000 BTU Natural Gas Indoor.
| Criterion | Rinnai RUCS75iN Natural Gas | APUS 140,000 BTU Natural Gas Indoor |
|---|---|---|
| Our rating | 6.6/10 | 6.7/10 |
| Max flow | 7.5 GPM | 6.8 GPM |
| Gas input | Not stated | 140,000 BTU/h |
| Efficiency | Not stated | 0.81 UEF |
| Temperature hold | Not stated | ±1 °F stated |
| Buyer reviews | 91 · 4.4/5 | 102 · 4.0/5 |
Pick the APUS 140,000 BTU Natural Gas Indoor if you want our higher-rated option (6.7/10), with a bigger burner (140,000 BTU/h) and a stated 0.81 UEF; stay with the Rinnai RUCS75iN Natural Gas for more flow (7.5 GPM) and a higher buyer rating (4.4/5).
We rate it 6.6/10 (good). It is based on 91 buyer reviews averaging 4.4/5 and the specifications stated in the listing.
The listing states a maximum flow of 7.5 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.
Yes, the listing says indoor mounting. That means a vent route to the outside, combustion air and a gas line sized for the unit, all as the maker and your local code require. A licensed plumber or gas fitter sorts that out.
Its listing states up to 7.5 GPM. 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. Vent and gas line: a licensed plumber or gas fitter confirms the vent route, the combustion air and a gas line that can deliver its full input. Get that quote before you order; our installation guide lists what they will ask. The warranty terms: 1 years are stated. Read what it requires: a licensed install, the gas type and regular flushing are the usual conditions. 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 and 91 buyer reviews, read line by line and weighed with our published formula.