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Rheem RTGH 8.4 GPM Natural Gas Indoor

Product images: Amazon listings

Rheem RTGH 8.4 GPM Natural Gas Indoor Review

7.3Good · out of 10#4 of 5 in our Indoor Natural Gas Tankless Water Heaters ranking

Written from the listing and 60 buyer reviews, not from our own use · How we rate

We like the Rheem RTGH 8.4 GPM Natural Gas Indoor for the mix: an 8.4 GPM maximum flow, condensing efficiency and a ±1 °F temperature hold. It earned a spot in our top 5 indoor natural gas tankless water heaters, and it's built for a two-bathroom house with one shower running at a time.

Variants of this model

These are sold as variants of one listing family. Each variant has its own page.

Price$1,168.99Price on Sep 30, 2026 · may have changed
Check the price on Amazon ↗ Rheem RTGH 8.4 GPM Natural Gas Indoor (opens in a new tab)Affiliate link · price and stock on Amazon
Compare side by side ↗
Specifications
BrandRheem
CategoryGas tankless water heaters
FuelNatural gas
Stated mounting locationIndoor
Stated maximum flow8.4 GPM
Stated gas input157,000 BTU/h
Condensing designStated in the listing title
Flow at a stated rise8.4 GPM at a 35 °F rise
Temperature hold±1 °F, per the listing
Freeze protectionStated in the listing
Stated warranty15 years on the heat exchanger
Buyer reviews60 · 4.4/5
ASINB0C8265TNX

Full listing title: Rheem RTGH Series 8.4 GPM Natural Gas Tankless Water Heater Indoor | 157,000 BTUs Super High Efficiency On Demand, Continuous Hot Water | Condensing Ultra-Low Nox

Listing evidence
FuelNatural Gas Full listing title
Stated mounting locationIndoor Full listing title
Stated maximum flow8.4 GPM Full listing title
Stated gas input157,000 BTUs Full listing title
Condensing designCondensing Full listing title
Updated October 2026
Exact listing, ASIN B0C8265TNX
Rating from a published formula

Compared with its closest rivals

The two picks next to it in our indoor natural gas tankless water heaters ranking, with their rating and a dated price.

Compare side by side ↗

Rheem RTGH 8.4 GPM Natural Gas Indoor

Rheem RTGH 8.4 GPM Natural Gas Indoor

7.3Good · out of 10$1,168.99 Price on Sep 30, 2026 · may have changed
  • Stated: 8.4 GPM · 157,000 BTU/h
  • 60 buyer reviews
  • Gas tankless water heaters
This product ↑
Rheem RTG 9.5 GPM Natural Gas Indoor

Rheem RTG 9.5 GPM Natural Gas Indoor

7.2Good · out of 10$1,047.92 Price on Sep 30, 2026 · may have changed
  • Stated: 9.5 GPM · 199,900 BTU/h
  • 88 buyer reviews
  • Gas tankless water heaters
See the review ↗

Up to 8.4 GPM from a 157,000 BTU burner

That's the maximum flow the listing states, at a 35 °F 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.

Why it made our list

What changes in the morning shower rush

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.

±1 °F hold. The burner adjusts as the flow changes, so the shower stays where you set it when somebody opens the kitchen tap. On paper, at least: that is the seller's claim.

One shower at a time, or two?

Two at once: up to 8.4 GPM, and our calculator counts a shower at 2 GPM, so that's two showers and a tap on paper. The listing gives 8.4 GPM at a 35 °F rise and the seller says it serves up to 3 showers. The maker's flow chart at a 63 °F rise tells you how much of that is left in January.

One at a time: you'd be paying for burner, gas line and vent you never use. A smaller unit is the cheaper answer.

Great for you if…

  • You run one shower and the kitchen tap at once, rarely more
  • You care about the gas bill as much as the hot water
  • A shower that suddenly runs cold drives you mad

Skip it if…

  • You simply want our top pick: that's the MIZUDO 199,000 BTU Natural Gas Indoor (9.2/10)
  • The far bathroom already waits a minute for hot water: no built-in recirculation is named

Gas, venting and what's in the box

What the Rheem RTGH 8.4 GPM Natural Gas Indoor listing names:

  • Up to 8.4 GPM
  • 8.4 GPM at a 35 °F rise
  • 157,000 BTU/h input
  • Natural gas
  • Indoor mounting
  • Condensing
  • ±1 °F temperature hold claimed
  • Freeze protection named
  • Low NOx
  • CSA, ETL or UL mark named

Warranty & support: 15-year warranty on the heat exchanger, as stated in the listing · CSA, ETL or UL certification named in the listing.

That is the maker's promise, not ours. Keep the invoice, register the Rheem RTGH 8.4 GPM Natural Gas Indoor 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.

Rheem RTGH 8.4 GPM Natural Gas Indoor, view 3

Price and cost per GPM of stated flow

$1,168.99 Price on Sep 30, 2026 · may have changed

At the price on Sep 30, 2026, each GPM of stated maximum flow works out at about $139.17 (price ÷ stated GPM, our arithmetic). That puts it in the pricier third of the 45 indoor gas tankless heaters we have a price and a stated flow for.

The heater is often the smaller half of the bill: the venting, a gas line that may need upsizing and a licensed installer's day come on top.

The button opens the exact listing (ASIN B0C8265TNX), where today's price, stock and seller apply. Sizes and variants of the same family often sit at different prices.

Rheem RTGH 8.4 GPM Natural Gas Indoor, view 4

A better fit for your house?

Two showers and the dishwasher at once? The Rinnai RU199iN Condensing (7.8/10) states up to 11 GPM.

No easy route for a vent pipe? The A. O. Smith 10 GPM Natural Gas Outdoor (8.0/10) mounts on an outside wall, per its listing.

On propane, not natural gas? The Rheem RTGH 9.5 GPM Propane Indoor (7.8/10) runs on propane.

Our take

The verdict

Our favourite thing about the Rheem RTGH 8.4 GPM Natural Gas Indoor is an 8.4 GPM maximum flow, closely followed by condensing efficiency. Only 60 buyers have rated it so far (4.4/5), so treat the score as an early read. The one thing that bugs us: the MIZUDO 199,000 BTU Natural Gas Indoor sitting above it at 9.2/10. We'd pick it if you run one shower and the kitchen tap at once, rarely more; otherwise, put it next to the Rinnai RU199iN Condensing first.

Check the price on Amazon ↗ Rheem RTGH 8.4 GPM Natural Gas Indoor (opens in a new tab)Affiliate link · price and stock on AmazonSee the indoor natural gas tankless water heaters ranking →

Living with it

Install day

Old tank out, unit on the wall, vent through the wall or the roof. Plan the gas line for 157,000 BTU/h; a licensed pro handles it, and often a permit.

The first shower

Hot water arrives after the cold already in the pipes, then stays (within ±1 °F, per the listing). A trickle from a bathroom tap may not light the burner; open it a bit more.

The first winter

January water comes in colder, so the same unit gives fewer GPM. The listing's 8.4 GPM is at a 35 °F rise; a northern winter asks for about 63 °F. Stagger the showers if you sized it tight.

Once a year

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 clean the inlet filter. Our flushing and descaling guide has the checklist.

What buyers say

Buyers give it 4.4/5, a strong record, above this ranking's 4.3 average. 60 reviews is still a modest pile, so a handful of new ones can move it.

The numbers
Buyer rating
4.4/5
Reviews
60
This ranking's average
4.3/5

The one thing we'd check first

Before you order the Rheem RTGH 8.4 GPM Natural Gas Indoor, check your winter rise: it is rated 8.4 GPM at a 35 °F rise, and a northern winter asks for nearer 63 °F.

Before you buy

Your winter flow

Find your winter inlet temperature (your water utility or a thermometer at the cold tap in January), subtract it from 105 °F, and read the maker's flow chart at that rise. 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 157,000 BTU/h. Get that quote before you order; our installation guide lists what they will ask.

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.

How it compares

How the Rheem RTGH 8.4 GPM Natural Gas Indoor stacks up against the closest alternative in our ranking, the Rinnai RU199iN Condensing.

CriterionRheem RTGH 8.4 GPM Natural Gas IndoorRinnai RU199iN Condensing
Our rating7.3/107.8/10
Max flow8.4 GPM11 GPM
Gas input157,000 BTU/hNot stated
Temperature hold±1 °F statedNot stated
Warranty15 years (heat exchanger)Not stated
Buyer reviews60 · 4.4/5388 · 4.4/5

Pick the Rinnai RU199iN Condensing if you want our higher-rated option (7.8/10), with more flow (11 GPM); stay with the Rheem RTGH 8.4 GPM Natural Gas Indoor for a bigger burner (157,000 BTU/h) and a stated ±1 °F hold.

Compare side by side ↗See the Rinnai RU199iN Condensing review →
The score in detail

How we rated it

Our score: 7.3/10

Buyer rating (45%)

39.6 / 45

4.4/5 average

Review volume (35%)

16.9 / 35

60 buyer reviews

Documented specifications (20%)

16.6 / 20

83/100 listing documentation score

Our rating is an evidence index on a 0–10 scale. It is not a buyer star rating, and we have not used the product ourselves.

  • Buyer rating (45%): the captured average shown on this variant's own listing page (not shared with the other Rheem variants), damped when there are fewer than 50 reviews.
  • Review volume (35%): more reviews mean more reliable evidence, on a logarithmic scale up to 5,000 reviews.
  • Documented specifications (20%): how completely the exact listing documents the attributes that matter.

Our editors then look at how it compares with the other heaters we rate. A commission is never an input to the rating. Read the full methodology.

Read the methodology →

Frequently asked questions

Is the Rheem RTGH 8.4 GPM Natural Gas Indoor any good?

We rate it 7.3/10 (good), #4 of 5 in our indoor natural gas tankless water heater ranking. It is based on 60 buyer reviews averaging 4.4/5 and the specifications stated in the listing.

How much hot water can the Rheem RTGH 8.4 GPM Natural Gas Indoor deliver?

The listing states a maximum flow of 8.4 GPM and a gas input of 157,000 BTU/h. 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.

Can the Rheem RTGH 8.4 GPM Natural Gas Indoor be installed indoors?

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.

What do you get with the Rheem RTGH 8.4 GPM Natural Gas Indoor?

Its listing states up to 8.4 GPM, a condensing heat exchanger, temperature held within ±1 °F, freeze protection and a 15-year heat exchanger warranty. 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.

What should I check before ordering the Rheem RTGH 8.4 GPM Natural Gas Indoor?

Your winter flow: find your winter inlet temperature (your water utility or a thermometer at the cold tap in January), subtract it from 105 °F, and read the maker's flow chart at that rise. 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 157,000 BTU/h. Get that quote before you order; our installation guide lists what they will ask. 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.

Where can I buy the Rheem RTGH 8.4 GPM Natural Gas Indoor?

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.

Have you used the Rheem RTGH 8.4 GPM Natural Gas Indoor yourselves?

No, we haven't used it ourselves. Everything on this page comes from its listing and 60 buyer reviews, read line by line and weighed with our published formula.

Keep comparing

If the Rheem RTGH 8.4 GPM Natural Gas Indoor hasn't sold you yet, see where it ranks, read the guides that feature it or browse all gas tankless water heaters.

Where it ranks

Best Tankless Water Heaters in 2026 →Best High-Efficiency Condensing Tankless Water Heaters in 2026 →Best Gas Tankless Water Heaters in 2026 →Best Whole-House Tankless Water Heaters in 2026: Gas and Electric →

Read this before you buy

Condensing vs non-condensing tankless water heaters: the difference →
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