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Rheem RTG 8.4 GPM Natural Gas Outdoor Review

Name: Rheem RTG 8.4 GPM Natural Gas Outdoor
Brand: Rheem
SKU: B0C826RQH9

7.7Very good · out of 10Rated from the listing's specs, no buyer reviews yet

Written from the listing's specs, not from our own use · How we rate

We like the Rheem RTG 8.4 GPM Natural Gas Outdoor for the mix: up to 8.4 GPM, an outside-wall install with no vent run and temperature held within ±1 °F. Add a 15-year heat exchanger warranty and it makes a good match for replacing a 40-gallon tank in a mid-size home.

Price$964.10Price on Sep 30, 2026 · may have changed

Check the price on Amazon ↗Affiliate link · price and stock on Amazon

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Specifications

Brand	Rheem
Category	Gas tankless water heaters
Fuel	Natural gas
Stated mounting location	Outdoor
Stated maximum flow	8.4 GPM
Stated gas input	180,000 BTU/h
Flow at a stated rise	8.4 GPM at a 35 °F rise
Temperature hold	±1 °F, per the listing
Freeze protection	Stated in the listing
Stated warranty	15 years on the heat exchanger
ASIN	B0C826RQH9

Full listing title: Rheem RTG Series 8.4 GPM Natural Gas Tankless Water Heater Outdoor | 180,000 BTUs High Efficiency On Demand, Continuous Hot Water | Non-Condensing

Listing evidence

Fuel	Natural Gas Full listing title
Stated mounting location	Outdoor Full listing title
Stated maximum flow	8.4 GPM Full listing title
Stated gas input	180,000 BTUs Full listing title

Updated October 2026

Exact listing, ASIN B0C826RQH9

Rating from a published formula

Compared with its closest rivals

Two gas tankless heaters on natural gas too, with about the same flow, closest to it on our rating, each with a dated price.

Compare side by side ↗

Rheem RTG 8.4 GPM Natural Gas Outdoor

7.7Very good · out of 10$964.10 Price on Sep 30, 2026 · may have changed

Stated: 8.4 GPM · 180,000 BTU/h
Gas tankless water heaters

This product ↑

Rheem RTG 7.0 GPM Natural Gas Outdoor

7.6Very good · out of 10$819.08 Price on Sep 30, 2026 · may have changed

Stated: 7 GPM · 160,000 BTU/h
Gas tankless water heaters

See the review ↗

Westinghouse Natural Gas Outdoor

7.5Very good · out of 10$799.96 Price on Sep 30, 2026 · may have changed

Stated: 8.1 GPM · 180,000 BTU/h · 120 V
Gas tankless water heaters

See the review ↗

Up to 8.4 GPM from a 180,000 BTU burner

That's the maximum flow the listing states, at a 35 °F rise. A cold January asks for a 63 °F rise (42 °F in, 105 °F out), and at that rise every tankless gives less than its headline; the maker's chart says how much. 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

What changes in the morning shower rush

Mounts outside. No vent pipe through the roof or the rim joist: it hangs on an outside wall and breathes on its own. The listing states freeze protection, which typically needs power at the wall to work.

±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.

Mild winters or hard freezes?

Mild winters: the Rheem RTG 8.4 GPM Natural Gas Outdoor goes on an outside wall, which saves the vent pipe and keeps the closet free.

Hard freezes: the listing names freeze protection, which needs power at the wall. Plan for the night the power goes out and the thermometer drops: draining it is the fallback.

Great for you if…

You run one shower and the kitchen tap at once, rarely more
There is no good vent route inside your house
A shower that suddenly runs cold drives you mad

Skip it if…

Your winters freeze hard and the outside wall has no power for freeze protection
You'd rather wait for buyer reviews: none are captured for this listing yet
You want the high-efficiency kind: the listing doesn't call it condensing

Gas, mounting and what's in the box

What the Rheem RTG 8.4 GPM Natural Gas Outdoor listing names:

Up to 8.4 GPM
8.4 GPM at a 35 °F rise
180,000 BTU/h input
Natural gas
Outdoor mounting
±1 °F temperature hold claimed
Freeze protection named
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 RTG 8.4 GPM Natural Gas Outdoor if the maker asks, and read the install conditions: many tankless warranties need a licensed install and regular flushing.

The installation manual has the last word on venting, gas line and clearances; your installer reads it before you order.

Rheem RTG 8.4 GPM Natural Gas Outdoor, view 3

Price and cost per GPM of stated flow

$964.10 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 $114.77 (price ÷ stated GPM, our arithmetic). That puts it around the middle of the 32 outdoor tankless heaters we have a price and a stated flow for.

No vent run to pay for, but the gas line, the water lines to the outside wall and an outlet for the freeze protection still come on top.

The button opens the exact listing (ASIN B0C826RQH9), where today's price, stock and seller apply.

Rheem RTG 8.4 GPM Natural Gas Outdoor, view 4

A better fit for your house?

Hard freezes where you live? The Ranein 190,000 BTU Natural Gas Indoor (7.9/10) is an indoor unit, out of the frost.

Want the high-efficiency kind? The A. O. Smith 10 GPM Natural Gas Outdoor (8.0/10) is a condensing unit, per its listing.

Only one bathroom? The Westinghouse 120,000 BTU Propane Outdoor (7.6/10) states up to 5.1 GPM.

Our take

The verdict

We like the Rheem RTG 8.4 GPM Natural Gas Outdoor for up to 8.4 GPM and an outside-wall install with no vent run. No buyer has reviewed it yet, so our 7.7/10 comes from the spec sheet alone. The catch with this Rheem outdoor tankless heater: the headline GPM is a mild-weather figure, so leave yourself margin for January. We'd pick it if you run one shower and the kitchen tap at once, rarely more; otherwise, put it next to the A. O. Smith 10 GPM Natural Gas Outdoor first.

Check the price on Amazon ↗Affiliate link · price and stock on AmazonAll gas tankless water heaters →

Living with it

Install day

It goes on an outside wall, with gas, water and power run to it. Plan the gas line for 180,000 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), and clear leaves and wasp nests from the cabinet vents. Our flushing and descaling guide has the checklist.

The one thing we'd check first

Before you order the Rheem RTG 8.4 GPM Natural Gas Outdoor, 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.

The outside wall

Pick a wall away from windows and doors, with power for the controls and the freeze protection the listing mentions. Our indoor vs outdoor guide compares the two installs.

The warranty terms

15 years are stated on the heat exchanger. 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.

How it compares

How the Rheem RTG 8.4 GPM Natural Gas Outdoor stacks up against the closest alternative, the A. O. Smith 10 GPM Natural Gas Outdoor.

Criterion	Rheem RTG 8.4 GPM Natural Gas Outdoor	A. O. Smith 10 GPM Natural Gas Outdoor
Our rating	7.7/10	8.0/10
Max flow	8.4 GPM	10 GPM
Gas input	180,000 BTU/h	199,000 BTU/h
Efficiency	Not stated	Condensing
Temperature hold	±1 °F stated	Not stated

Pick the A. O. Smith 10 GPM Natural Gas Outdoor if you want our higher-rated option (8.0/10), with more flow (10 GPM) and a bigger burner (199,000 BTU/h); stay with the Rheem RTG 8.4 GPM Natural Gas Outdoor for a stated ±1 °F hold.

Compare side by side ↗See the A. O. Smith 10 GPM Natural Gas Outdoor review →

The score in detail

How we rated it

Spec-based rating on a 4.5–8.5 scale: 4.5 + average of the 4 criteria × 0.4. Capped at 8.5 because no customer evidence is included.

Key specifications

9 / 10

Build, warranty & certifications

8 / 10

Listing documentation

7 / 10

Fit & compatibility

8 / 10

This product has no captured buyer-review record yet, so its rating comes from the documented listing alone: four criteria scored out of 10 (key specifications; build, warranty and certifications; listing documentation; fit and compatibility), placed on a 4.5–8.5 scale. Read the full methodology.

Read the methodology →

Frequently asked questions

Is the Rheem RTG 8.4 GPM Natural Gas Outdoor any good?

We rate it 7.7/10 (very good). The rating comes from its documented listing alone, as no customer-review record is captured yet.

How much hot water can the Rheem RTG 8.4 GPM Natural Gas Outdoor deliver?

The listing states a maximum flow of 8.4 GPM and a gas input of 180,000 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 RTG 8.4 GPM Natural Gas Outdoor be installed indoors?

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.

What do you get with the Rheem RTG 8.4 GPM Natural Gas Outdoor?

Its listing states up to 8.4 GPM, outdoor mounting that skips the flue, temperature held within ±1 °F 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 RTG 8.4 GPM Natural Gas Outdoor?

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. The outside wall: pick a wall away from windows and doors, with power for the controls and the freeze protection the listing mentions. Our indoor vs outdoor guide compares the two installs. The warranty terms: 15 years are stated on the heat exchanger. 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.

Where can I buy the Rheem RTG 8.4 GPM Natural Gas Outdoor?

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 RTG 8.4 GPM Natural Gas Outdoor yourselves?

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.

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