We checked real listings and manufacturer specs for five tankless water heaters from Rheem, Rinnai, EcoSmart, A.O. Smith and Bosch, comparing GPM, efficiency and fuel type.
Rheem
Why we like it
Rinnai
Why we like it
EcoSmart
Why we like it
A.O. Smith
Why we like it
Bosch
Why we like it| Product | Rank | Brand | Best For | Score |
|---|---|---|---|---|
| Rheem Performance Platinum 9.5 GPM Natura... | #1 | Rheem | Best for Smart Home Integration | 9.8 |
| Rinnai RU199iN Condensing Tankless Hot Wa... | #2 | Rinnai | Best Reviewed Whole-House Gas Unit | 9.6 |
| EcoSmart ECO 27 Tankless Water Heater, El... | #3 | EcoSmart | Best Whole-Home Electric (No Gas Line Needed) | 9.4 |
| AO Smith ATHR-199X3 Adapt 10.5 GPM Energy... | #4 | A.O. Smith | Best Scale Protection | 9.3 |
| Bosch Thermotechnology 7736505868, 4.5kW,... | #5 | Bosch | Best Point-of-Use / Single-Sink Solution | 9.1 |
Buyer checklist
This is desk research, not a hands-on installation or flow-rate test — we did not install and run these five units ourselves. We pulled each candidate's specifications from a combination of real Amazon.com listings (using cached Wayback Machine snapshots where useful) and each manufacturer's own current product pages, since three of the five brands' Amazon listings had no accessible cached snapshot during this research pass. We're disclosing this gap directly: for the Rheem, EcoSmart and A.O. Smith entries in this guide, we could not retrieve a working Amazon listing snapshot with visible star ratings, so specs come from each manufacturer's own official product page instead, and we are not stating an Amazon star rating for those three products. A naming note on the A.O. Smith entry specifically: our original draft referenced "A.O. Smith Signature Premier," and real Amazon listings under that exact name do exist, but A.O. Smith's current official website (hotwater.com) no longer markets a "Signature Premier" line — its current flagship condensing gas tankless line is branded "Adapt." We describe the current Adapt line here rather than the apparently-discontinued Signature Premier name, and flag this naming shift explicitly. Gas tankless units (Rheem, Rinnai, A.O. Smith) require a gas line and proper venting and are generally professionally installed; electric tankless units (EcoSmart, Bosch) require dedicated high-amperage circuits appropriate to their kW rating. None of these are simple DIY swaps for a typical homeowner — budget for licensed installation regardless of which type you choose, and confirm your home's existing gas line capacity or electrical panel capacity before purchasing a specific model.
UEF is a standardized efficiency rating for water heaters — a higher number means more of the energy input actually goes into heating water rather than being lost as waste heat or in standby losses. Per the manufacturers' own materials, the units in this guide range from about 0.93 to 0.95 UEF for the higher-end condensing gas models, which is considered high efficiency for this category.
Technically often yes, but it's a significant project, not a simple swap — switching fuel types means running new gas lines or new high-amperage electrical circuits, which requires licensed professionals and may involve permitting. If you're already set up for one fuel type, staying with that type (as this guide's Rheem/Rinnai/A.O. Smith gas options versus EcoSmart/Bosch electric options) is usually the simpler and cheaper path.
They solve different problems. A whole-house unit (Rheem, Rinnai, EcoSmart, A.O. Smith in this guide) is sized to supply hot water to your entire home's fixtures. A point-of-use unit (the Bosch here) is a smaller, lower-output unit installed close to one specific sink or fixture, typically to eliminate a long wait for hot water to travel from a distant central heater, not to replace your home's primary water heater.
During this research pass, we could not retrieve a working cached Amazon listing snapshot with visible ratings for these three products, so we sourced their specs from each manufacturer's own official product page instead and disclosed that gap here rather than presenting an unverified number.