Rheem RRTGH84DVLN3701171 Rheem RTGH Series 8.4 GPM 157,000 BTU 120 Volt Residential Indoor Natural Gas Tankless Water Heater Stainless Steel

Why I chose this Rheem tankless and what stood out

I replaced an aging tank-style heater with the Rheem RTGH 8.4 GPM indoor natural gas unit to gain space, cut standby losses, and get steadier hot water to multiple fixtures. After several weeks of daily use, it’s proven to be a compact, quiet, and capable workhorse with a few install and setup nuances to plan for.

At 17-11/16 inches wide, the unit freed up a surprising amount of floor space in my utility room. The stainless-steel build feels robust, the controls are straightforward, and the temperature range (100–140°F, default 120°F) covers typical whole-home needs. It’s a 120V, electronically ignited, condensing tankless rated up to 157,000 BTU with a listed flow window of 0.4–8.4 GPM and a 0.93 efficiency rating. In practice, those numbers translate into solid, predictable performance—provided you size it realistically and install it correctly.

Installation notes: the important details

• Venting and air intake: This is a sealed-combustion, direct-vent unit. Plan your intake and exhaust runs carefully and check your local code for materials and termination clearances. The intake/exhaust port geometry is compact but a bit cramped; getting both runs aligned cleanly took more patience than I expected. If you can use a concentric vent kit, it simplifies wall penetration and looks cleaner outside.

• Condensate management: Being a condensing model, you must route condensate to a drain and, ideally, through a neutralizer. Don’t skip this—corrosive condensate can damage drain lines and is a code issue in many jurisdictions.

• Gas supply: At 157,000 BTU, adequate gas line sizing is critical. Undersized lines cause low input and unstable temperatures under load. If you’re upsizing from a small tank heater, expect to evaluate and potentially upgrade your gas run.

• Electrical: It needs a dedicated 120V receptacle. No power, no hot water. If outages are common where you live, consider a small UPS that’s compatible with gas appliances.

• Water quality and pressure: This unit wants consistent inlet pressure and reasonably clean water. I installed full-port isolation valves and service ports, plus a simple inline sediment filter. If your home has a pressure-reducing valve, ensure it’s tuned correctly. An expansion tank may be required on closed systems.

I did the prework and had a licensed plumber perform the final gas and vent connections. It ran on the first try, and after a brief bleed of air from lines, it delivered stable hot water.

Performance and real-world flow

The headline flow of 8.4 GPM is a best-case scenario at a modest temperature rise. A more useful way to think about capacity is by temperature rise:

• 70°F rise (typical in colder climates): roughly 4.5 GPM
• 50°F rise (milder climates): roughly 6+ GPM

In my mixed-climate home, I can run a shower and the dishwasher comfortably, or two showers at once, with stable outlet temperature. During a stress test—shower, washing machine filling warm, and a sink running—I noticed the unit modulate without major swings, as long as total demand stayed within those realistic limits.

Activation at low flow is good. The burner typically lights at about 0.4 GPM, so handwashing or a trickle from a single fixture still produces warm water. If you love ultra-low-flow showerheads, you’ll want to verify they can maintain enough flow to keep the burner engaged.

Temperature stability and comfort

Temperature stability is strong once the setpoint and fixture flows settle. A common tankless gripe is the “cold-water sandwich.” I didn’t see much of that here after the first second or two—Rheem’s modulation tracks flow nicely. If you’re feeding thermostatic shower valves, keep the unit at 120°F and let mixing occur at the valve; for certain tub-filling tasks, I temporarily bump setpoint to 130–140°F and then bring it back down.

Noise levels are low. Ignition is a soft whoosh rather than a bang, and the fan hum is easy to tune out behind a closed door.

Controls and usability

The front panel provides simple up/down temperature adjustments and a clear digital readout. Out of the box, mine was set at 120°F; raising to 140°F was straightforward. Fault codes are displayed plainly. I did trip a P1 flow-related alert once during early testing—it turned out to be a partially clogged faucet aerator coupled with some trapped air in the lines. Cleaning the aerator and purging the line solved it. It’s also smart to check the unit’s inlet filter screen during commissioning.

Efficiency and exhaust considerations

At a 0.93 efficiency rating, this is a true condensing tankless. My gas usage has dropped versus a constant-standby tank model, especially noticeable in shoulder seasons when hot water demand is intermittent. Combustion and condensate byproducts are normal: you’ll see a visible vapor plume in cool weather, and there’s a faint combustion odor at the termination. Position the vent away from patios or windows you often open.

Maintenance outlook

Tankless systems are not “install and forget.” Plan on:

• Annual descaling in hard-water regions (service valves make this easy).
• Cleaning the inlet water filter screen.
• Inspecting vent terminations and condensate drain.
• Verifying combustion air intake is clear.
• Checking all unions for weeping, especially after seasonal temperature swings.

The good news: access is straightforward, and the stainless-steel components look built for the long haul. Rheem’s warranty—15 years on the heat exchanger, 5 on parts, 1 year labor—adds peace of mind, but you’ll want documented maintenance on file.

What I liked

• Compact footprint with a quality stainless-steel build.
• Strong, steady hot water for a typical household without temperature hunting.
• Low activation flow and quiet operation make it “invisible” in daily use.
• Simple controls with an easy path to 140°F when needed.
• Thoughtful protection: electronic ignition and solid safety routines.

What I’d change

• Intake/exhaust port spacing and collars could be friendlier; tight clearances make for fiddly installs.
• Documentation on condensate neutralization and venting materials could be more prominent; new-to-condensing owners often underestimate this step.
• Like all tankless systems, it’s sensitive to inadequate gas supply and water-side flow restrictions. Expect to do some system housekeeping during setup.

Who it’s for

• Households that want space savings, lower standby losses, and on-demand hot water.
• Homes with access to natural gas and a feasible direct-vent path to an exterior wall or roof.
• Users comfortable with basic annual maintenance or willing to hire it out.
• Small to mid-size families in mild-to-moderate climates can run multiple fixtures comfortably. In very cold climates, consider your simultaneous-use habits and potentially step up to a higher-BTU model if you regularly run three or more hot fixtures at once.

The bottom line

The Rheem RTGH 8.4 GPM unit delivers what a modern indoor tankless should: reliable, efficient hot water in a compact package. It rewards good planning—proper venting, gas sizing, condensate handling, and a quick check of aerators and inlet filters. Once set up correctly, it’s quiet, consistent, and easy to live with.

Recommendation: I recommend this Rheem tankless for most homeowners looking to replace a standard tank with an efficient, space-saving system. It hits a sweet spot of performance and ease of use, with enough headroom for typical two-fixture demand and the ability to set 140°F when needed. Just approach installation thoughtfully—especially venting and gas supply—and keep up with simple annual maintenance to get the best from it over the long term.