Every other retailer guide on this site covers a store you walk into or a bundled program you book. Amazon is different — it’s the widest shelf of any retailer here, but it’s also the one where the seller behind the listing matters as much as the price. Here’s what’s actually buyable, what isn’t, and the warranty detail that trips people up.
What’s actually sold on Amazon, by category
| Electric (EcoSmart / Rheem RTEX) | Rheem Performance Platinum (gas) | Rinnai Sensei (gas) | Navien NPE-A2 (gas) | |
|---|---|---|---|---|
| Sold on Amazon? | Yes, broadly | Yes | Yes | No |
| Typical seller | Amazon or brand storefront | Amazon or brand storefront | Mix of Amazon + 3rd-party | Wholesale distributors only |
| Price range seen | ~$152–$642 | ~$1,280–$1,430 | ~$1,050–$1,850 | Trade-account pricing only |
| Warranty risk | Low | Low | Verify "Authorized E-Tailer" seller | N/A (not on Amazon) |
Prices and listings per Amazon.com, Ace Hardware, and manufacturer/distributor sites as of October 2026; marketplace pricing and stock change without notice and vary by seller.
By the numbers
- 12 to 15 years — Rinnai’s standard heat-exchanger warranty term, with Smart Connect app registration adding up to 4 more years of labor coverage on eligible models. — per Rinnai’s published warranty terms
- $470 vs. ~$580 — the EcoSmart ECO 27’s typical Amazon price against Ace Hardware’s and AOK Power’s listed price for the same 27kW unit, a real gap rather than a wash. — per Amazon.com and Ace Hardware listings
- Zero — the number of Navien NPE-A2 listings found directly on Amazon; the line is distributed through plumbing wholesalers like Ferguson, First Supply, and APFS instead, several of which require a trade account before pricing is even visible. — per distributor websites
1. EcoSmart ECO 27 — Best Electric Pick, and the Clearest Amazon Price Win
EcoSmart ECO 27 240V Electric Tankless Water Heater
- Sold and typically fulfilled directly through Amazon or EcoSmart's own storefront — not a marketplace reseller gray area, unlike some of Rinnai's gas listings below.
- At roughly $470, it undercuts the ~$580 price seen at Ace Hardware and AOK Power for the same self-modulating 27kW model, per our EcoSmart lineup guide.
- 27kW needs a dedicated high-amperage circuit — confirm panel capacity before ordering, since this is whole-home electric territory, not a point-of-use add-on.
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2. Rinnai Sensei RX199iN — Best Gas Pick, With a Seller Caveat
Rinnai Sensei RX199iN Condensing Gas Tankless Water Heater
- One of four Rinnai Sensei models commonly found on Amazon (alongside the RX160iN, RE180iN, and RUCS75iN), per our Rinnai lineup guide — but listings mix Amazon-fulfilled stock with third-party marketplace sellers.
- Rinnai's 12- to 15-year heat-exchanger warranty only holds if the unit is purchased from a Rinnai Authorized E-Tailer — check the "Sold by" line on the listing, not just the Prime badge, before buying.
- Register through the Rinnai Central App after install to unlock up to 4 extra years of labor coverage on Smart Connect-enabled models.
Where Amazon’s selection actually ends
- Navien isn’t here at all. Unlike Rinnai, Navien’s NPE-A2 series is distributed almost entirely through professional plumbing wholesalers — Ferguson, First Supply, APFS, Pacific Plumbing, and FW Webb all carry it, and several require a trade account before pricing is even visible. That’s a deliberate wholesale-channel choice, the same pattern our best State tankless water heater guide covers for A.O. Smith’s wholesale-only sibling brand. If you want Navien specifically, our Navien lineup guide covers how to source and size one through a plumber instead.
- The seller line matters more than the Prime badge. A listing can carry Prime two-day shipping and still be fulfilled by a third-party marketplace seller rather than Amazon or the brand itself. For electric units and Rheem’s retail Performance Platinum line, that distinction rarely matters. For Rinnai’s gas lineup, it’s the difference between a warranty that holds and one that doesn’t if something fails.
- No bundled installation. Amazon sells the box, full stop. There’s no Home Services-style install booking at checkout the way Costco or Home Depot offer — budget for a separate licensed plumber or electrician quote, and see our installation guide for realistic timelines and permit requirements before you order.
The bottom line
Amazon is the widest single shelf for tankless water heaters on this site — EcoSmart’s electric lineup at a genuine price edge, Rheem’s retail gas line near parity with Home Depot, and most of Rinnai’s Sensei collection, all with Prime shipping. The catch is entirely about the seller, not the hardware: verify “Authorized E-Tailer” status before buying a Rinnai gas unit, and don’t expect to find Navien here at all — that line stays inside the plumbing wholesale channel. For every brand ranked side by side regardless of retailer, start with our best tankless water heater roundup; for the membership question itself, see whether Amazon Prime is worth it for a tankless install.