Rheem RTG Series 8.4 GPM Natural Gas Tankless Water Heater Outdoor
Rheem's 8.4 GPM outdoor natural gas tankless handles whole-house demand across 3-4 bathrooms and eliminates indoor venting entirely by mounting outdoors.
Updated
- Strong feedback from verified Amazon buyers
- 8.4 GPM flow rate -- whole-house capacity for 3-4 bathrooms
- Outdoor installation eliminates all venting requirements
- 180,000 BTU input handles high-demand scenarios
Best For / Not For
Best for
- Homes on natural gas that want the simplest install path -- no interior venting
- Households with 3-4 bathrooms that need full simultaneous-demand coverage
- Buyers replacing an outdoor gas appliance or installing in a mild climate with covered outdoor space
Not for
- Very cold climates where outdoor units risk freeze damage -- check Rheem's specs for minimum ambient temperature
- Homes without a covered outdoor mounting location protected from direct weather
- Buyers who need indoor installation
Key Details
The Case for Outdoor Installation
The biggest hidden cost of indoor gas tankless installation is venting. Non-condensing units require Category III stainless steel venting that runs to an exterior wall or roof -- materials alone can run several hundred dollars, plus labor. Condensing units need a plastic vent run but also require condensate drainage. Outdoor units bypass all of this. Mount it on an exterior wall near your gas line, connect water supply and return lines, run the gas drop, and the venting question is solved by physics: it exhausts straight to open air.
For homeowners who have an appropriate outdoor wall -- covered from direct rain, accessible for service, close enough to the gas line -- the outdoor installation path routinely saves several hundred dollars in install cost compared to running venting from an indoor mechanical room. The Rheem RTG is purpose-built for this path and the strong buyer feedback reflects buyers who completed installs successfully.
Flow Rate and Household Sizing
8.4 GPM at a 35°F temperature rise is genuine whole-house capacity. Two showers running simultaneously at 1.8 GPM each, plus a dishwasher at 1.5 GPM, totals 5.1 GPM -- comfortably within the unit's range. Adding a third fixture brings you to around 7 GPM, still covered. Where the RTG can be stressed is in very cold climates where winter groundwater at 35-40°F requires an 80°F rise to reach 115°F output, which cuts effective flow rate meaningfully.
In most of the continental US outside the northern tier states, this unit sizes correctly for a family of four to six in a three-to-four bathroom home. Verify your local winter groundwater temperature against Rheem's published flow rate curves for the RTG series if you are in a northern climate before purchasing.
Pros and Cons
Pros
- Strong feedback from verified buyers
- Outdoor installation eliminates the cost and complexity of indoor venting
- 8.4 GPM handles real whole-house simultaneous demand
- Rheem's service and parts network is strong across the US
- 180,000 BTU input maintains flow rate under high demand
Cons
- Requires a covered outdoor location -- direct weather exposure can shorten lifespan
- Not suitable for freezing climates without proper freeze protection
- Professional gas line and installation required
Bottom Line
Rheem RTG Series 8.4 GPM Outdoor is a Buy. It is the cleanest install path for whole-house natural gas tankless heating -- outdoor placement eliminates venting cost and complexity, and 8.4 GPM covers simultaneous demand across 3-4 bathrooms. Best for natural gas homes with a suitable covered outdoor mounting location.
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