If you have been shopping condensing tankless water heaters and keep coming back to the same name, there is a reason. The Rheem IKONIC series delivers 0.96 UEF efficiency, the industry's best heat exchanger warranty, and an optional built-in recirculation pump that eliminates the wait for hot water entirely. This guide covers every model in the residential and commercial IKONIC lineup — what separates them, how to pick the right one, and what makes this series worth speccing over the competition.
Browse the full Rheem IKONIC lineup at PlumbersCrib.com or contact our team with any sizing or spec questions.
What makes the IKONIC different
Rheem makes tankless water heaters across several series — Professional Classic, ThermaForce, and IKONIC. The IKONIC sits at the top of the condensing category and is set apart by four things that matter on every job:
- 0.96 UEF — among the highest Uniform Energy Factor ratings available in a residential gas tankless unit. Condensing efficiency captures heat from exhaust gases that a non-condensing unit vents outside, delivering more hot water per BTU of gas consumed
- Hot-Start Programming — keeps the unit in a ready state between back-to-back usage cycles, preventing the cold water sandwich that makes clients call back. This is one of the most common complaints about tankless units generally and Hot-Start addresses it directly
- Dual stainless steel heat exchangers — both primary and secondary exchangers are stainless steel, contributing to the 15-year heat exchanger warranty and long-term durability in hard water conditions
- Field gas convertibility — every IKONIC ships with the LP conversion kit included. One SKU covers both natural gas and propane jobs
S vs. SR: the one decision that matters most
Every IKONIC model comes in two configurations — the base S model and the SR model. The SR adds a built-in recirculation pump and built-in Wi-Fi via Rheem's EcoNet platform.
S models — standard tankless installation. Hot water delivered on demand when a fixture opens. No recirculation loop required. Simpler rough-in. The right choice for most new construction and retrofit jobs where immediate hot water delivery is not the primary concern or where a dedicated return line is not practical.
SR models — built-in recirculation pump keeps hot water circulating through the supply line so it is available at the fixture immediately. Eliminates the wait entirely. Also includes EcoNet Wi-Fi for remote control, scheduling, and monitoring via the Rheem app. Schedule the pump to run only during peak hours to save energy versus continuous circulation. The right choice for larger homes, clients who prioritize instant hot water, or any job where a recirculation loop is already roughed in.
Note: The SR recirculation pump requires a dedicated return line back to the unit. Where no return line exists, comfort flow systems using the cold water line as a return are an option — but this adds a brief delay to cold water delivery at fixtures. The EcoNet Wi-Fi also requires a 2.4GHz network at the installation location.
The full residential IKONIC lineup
| Model | BTU | Max GPM | UEF | Recirc + Wi-Fi |
|---|---|---|---|---|
| RTGH-S84i | 157,000 | 8.4 | 0.96 | No |
| RTGH-SR84i | 157,000 | 8.4 | 0.96 | Yes |
| RTGH-S10i | 180,000 | 10.1 | 0.96 | No |
| RTGH-SR10i | 180,000 | 10.1 | 0.96 | Yes |
| RTGH-S11i | 199,000 | 11.2 | 0.96 | No |
| RTGH-SR11i | 199,000 | 11.2 | 0.96 | Yes |
GPM note: All GPM figures are based on a 35°F temperature rise — the industry standard for comparing tankless output. Actual GPM at higher rise temperatures (colder inlet water in northern climates) will be lower. Use the ground water temperature zone map below to size correctly for your region.
Which model for which job
RTGH-S84i / SR84i — 8.4 GPM. The right choice for most single-family residential jobs in warm to moderate climates. Covers 2–3 simultaneous fixtures comfortably in southern and southwestern US zones. In colder northern climates with lower inlet water temperatures, size up to the S10i or S11i to maintain adequate flow at higher temperature rise.
RTGH-S10i / SR10i — 10.1 GPM. The most popular size for whole-house residential jobs in northern climates and larger homes across all regions. Covers 3–4 simultaneous fixtures and handles higher temperature rise without sacrificing flow. The SR10i with built-in recirculation is one of the most commonly specified units for high-end residential projects where instant hot water is a priority.
RTGH-S11i / SR11i — 11.2 GPM. The top of the residential IKONIC range. Suited for large homes in cold climates, high-demand households, or any project where the client wants maximum available flow with no compromise. Covers 4+ simultaneous fixtures and is the right call for luxury residential installs where hot water demand runs continuously throughout the day.
Sizing by climate: use the ground water temperature zone map
The single biggest sizing mistake with any tankless unit is ignoring inlet water temperature. Ground water temperature varies significantly by region — in cold northern states, incoming water can be as cold as 37°F in winter, which means the unit has to work much harder to reach 120°F delivery temperature. The map below shows US ground water temperature zones by region — use it to calculate your temperature rise before selecting a model.
To calculate temperature rise: subtract your region's ground water temperature from your target delivery temperature (typically 120°F). Then use the GPM output curve on the product spec sheet for your chosen model to confirm it delivers adequate flow at that rise. If you are in a zone 4 or 5 climate (cold northern states), size up to the S10i or S11i to be safe.
Where the IKONIC fits in the home
Garage installation
Laundry room installation
Game room installation
Outdoor installation (with conversion kit)
Installation requirements
All residential IKONIC models are indoor units. Key specs confirmed from the live product pages — always verify with the spec sheet for your exact model before ordering:
- Venting — PVC Category III or CPVC. Up to 70 ft on 2" pipe, 150 ft on 3" pipe. Can also vent through existing B-vent up to 50 ft. Concentric or two-pipe configurations both supported
- Gas line — 1/2" gas line compatible (subject to local code). Field-convertible from NG to LP — conversion kit included
- Water connections — 3/4" NPT inlet and outlet
- Electrical — 120V standard outlet. No dedicated circuit required
- Display — full-text digital display, no dip-switches. Error codes display in plain text for easier diagnostics on service calls
- Outdoor installation — not standard on any IKONIC model. Outdoor conversion kit (RTGH-SX) available separately
- Manufactured homes — approved for manufactured/mobile home installation
- Ultra Low NOx — compliant across all models
- High altitude — compatible across all models, confirm rating with spec sheet
The warranty — why it matters
The IKONIC carries the most comprehensive warranty in the residential condensing tankless category:
- 15 years — heat exchanger
- 5 years — parts
- 1 year — labor
The 15-year heat exchanger warranty is a legitimate differentiator — not a marketing claim. It is backed by dual stainless steel exchangers that resist corrosion and mineral scale significantly better than the copper or brass exchangers used in competing condensing units. For clients in hard water areas or those who plan to stay in their home long-term, this is a real argument for speccing the IKONIC over a less expensive condensing alternative.
Commercial IKONIC: CS11i and CSR11i
The IKONIC commercial models are designed for light commercial and multi-family applications where residential capacity is not sufficient. Both can be manifolded — up to 32 units connected together for large commercial hot water demand.
Frequently asked questions
What is the difference between the IKONIC and the standard RTGH condensing series?
Both are condensing units with 0.96 UEF, but the IKONIC adds Hot-Start Programming, dual stainless steel heat exchangers, the 15-year heat exchanger warranty, field LP convertibility with the kit included, and the SR recirculation option. The standard RTGH series uses a copper primary exchanger and carries a shorter warranty.
Does the IKONIC work with propane?
Yes — every IKONIC ships as a natural gas unit with the LP conversion kit in the box. No separate propane SKU needed.
Can it be installed outdoors?
All residential IKONIC models are indoor-only units. The outdoor conversion kit (RTGH-SX) is available separately for applications where outdoor installation is required.
Which size for a 4-bedroom home in a cold climate?
In cold northern climates where inlet water temperatures run 40–50°F, the temperature rise required to reach 120°F delivery is significantly higher, which reduces effective GPM. For a 4-bedroom home in a cold climate, the S10i or S11i is generally the right call. Use the ground water temperature zone map above to calculate the rise for your region before finalizing the spec.
Does the SR require a dedicated return line?
Yes — the built-in recirculation pump requires a dedicated hot water return line back to the unit for full functionality. Comfort flow systems using the cold water line as a return are an alternative where no return line exists, but add a brief delay to cold water delivery at fixtures.
Ready to order?
Browse the full Rheem IKONIC lineup at PlumbersCrib.com — all six residential models and both commercial models in stock with free shipping on orders over $199. Questions about sizing or which model is right for your job? Contact our team or call 877-881-5501 — we are here to help.