Quick Answer: The best tankless water heater for most homes with a gas line is the Rinnai Sensei RX199iN — a condensing 199,000 BTU unit rated up to 11.1 GPM (warm inlet) at a 0.98 UEF with WiFi control, $1,530–$1,725 street. It is the current name for the unit long sold as the RU199iN. The Navien NPE-240A2 is the pick if you want built-in recirculation for instant hot water, while the Rheem Performance Platinum 9.5 GPM is the best value at retail. No gas line? The Stiebel Eltron Tempra 36 Plus is the best whole-home electric unit, and the EcoSmart ECO 27 is the budget electric choice. Remember: every GPM rating below assumes a warm inlet — real flow drops in cold climates.
Last updated August 16, 2026 — reverified the EcoSmart ECO 27’s price across Amazon ($470), True Value ($609.99), and eBay ($389.50); our ~$570 estimate still sits inside that retailer spread, so no change needed. Rinnai Sensei RX199iN’s 0.98 UEF and 11.1 GPM spec reconfirmed against Rinnai’s own product page — no listed street price at the manufacturer level, so our $1,530-$1,725 wholesaler-checked range stands.
Last updated July 29, 2026 — reverified the Navien NPE-240A2’s UEF and price directly against Navien’s own spec sheet and current retailer pricing; the site-wide “0.96-0.97 UEF” figure was stale, corrected to Navien’s published 0.95.
A tankless (or “on-demand”) water heater fires only when you open a hot tap, so it never runs out and doesn’t waste energy keeping a tank warm 24/7. We compared gas, propane, and electric units across flow rate (GPM), efficiency (UEF), venting, and real install cost to find the ones worth buying in 2026. Because tankless GPM depends on how cold your incoming water is, we’ve framed every flow figure as a warm-climate maximum — your winter numbers will be lower.
Our top picks at a glance
| Model | Best for | Fuel | Max Flow / Power | Price |
|---|---|---|---|---|
| Rinnai Sensei RX199iN (formerly RU199iN) | Best overall | Natural gas | ~11.1 GPM · 199k BTU · 0.98 UEF | $1,530–$1,725 |
| Navien NPE-240A2 | Best with recirculation | Natural gas | ~11.2 GPM · 199k BTU · 0.95 UEF | ~$1,884 |
| Rheem Performance Platinum 9.5 | Best value (retail) | Gas / propane | 9.5 GPM · 199k BTU | ~$1,150 |
| Stiebel Eltron Tempra 36 Plus | Best whole-home electric | Electric 240V | 36 kW · ~7 GPM | ~$850 |
| EcoSmart ECO 27 | Best budget electric | Electric 240V | 27 kW · ~6.6 GPM | ~$570 |
By the numbers
- 24–34% more efficient than a storage tank for homes using 41 gallons/day or less (8–14% for high-use homes). — U.S. Department of Energy
- ~$95/year saved by a family of four with an ENERGY STAR gas tankless vs. a standard gas tank — roughly $1,800 over the unit’s life. — ENERGY STAR
- ~20 years typical tankless lifespan vs. 10–12 years for a tank. — DOE / industry
- The federal 25C tax credit is gone for 2026. The credit of up to $600 for qualifying high-efficiency gas tankless units was repealed by the One Big Beautiful Bill Act and expired for equipment placed in service after December 31, 2025 — a 2026 install gets no federal credit. Utility and state rebates are now the only incentives — see our tankless water heater cost guide and our rebate finder guide for what’s still available by state. — ENERGY STAR / Rewiring America
1. Rinnai Sensei RX199iN — Best Overall
Rinnai Sensei RX199iN Condensing Gas Tankless (formerly RU199iN)
- 199,000 BTU condensing burner delivers up to ~11.1 GPM in warm climates — enough for 2–3 fixtures at once.
- 0.98 UEF efficiency and PVC venting keep operating cost and install cost down versus non-condensing units.
- Built-in WiFi (Control-R) and a 15-year heat-exchanger warranty.
- Typically runs $100–$300 less than the comparable Navien.
The Sensei RX199iN is the unit we recommend to most homeowners with natural gas. It sits at the top of Rinnai’s condensing flagship line, and its 199k BTU output means it rarely runs short even when the laundry and a shower are both going. Rinnai rebranded this platform from RU199iN to Sensei RX199iN — the same 199,000 BTU condensing unit, rated at a 0.98 UEF, with a street price of $1,530–$1,725 that runs $100–$300 below the comparable Navien, per a 2026 master-plumber review by Mother. Either SKU is the right buy; the RX is the current stock, and remaining RU199iN listings are the same heater under the old name. Match natural gas vs. propane and indoor vs. outdoor to your setup — we rank the whole lineup, including the pump-equipped RXP, in our best Rinnai tankless water heater guide. For the full gas shortlist, see our best gas tankless water heater guide — and if a closeout price on a Takagi tempts you, read that guide first: the brand was discontinued by the manufacturer on December 31, 2025.
2. Navien NPE-240A2 — Best With Recirculation
Navien NPE-240A2 Condensing Gas Tankless
- ComfortFlow built-in recirculation pump and buffer tank cut the wait for hot water at the tap.
- Up to ~11.2 GPM at a 35°F rise and a 0.95 UEF, per Navien's own NPE-240A2 spec sheet.
- Class-leading 15-year heat-exchanger warranty.
If the annoyance you most want to solve is standing at the shower waiting for hot water, the Navien NPE-240A2 is the answer. Its built-in recirculation pump and small buffer tank tame the “cold-water sandwich” that plagues some tankless units, and the 15-year warranty is the longest here. You pay a little more than the Rinnai for those features. Navien sells three more sizes with the same built-in pump, plus a cheaper no-pump S2 series — see our full Navien lineup guide for the size-by-size breakdown.
3. Rheem Performance Platinum 9.5 GPM — Best Value
Rheem Performance Platinum 9.5 GPM (ECOH200) Gas Tankless
- Condensing 199,000 BTU unit rated 9.5 GPM — plenty for most 2–3 bath homes.
- ENERGY STAR certified with EcoNet WiFi; convertible for indoor or outdoor install.
- Sold at major retailers, so it's the easiest premium unit to buy and service yourself.
Rheem’s retail Performance Platinum line (the smart “ECOH” SKUs — not to be confused with Rheem’s pro RTGH series) is the value sweet spot in gas tankless. You get condensing efficiency, WiFi, and 9.5 GPM for a few hundred dollars less than the Rinnai or Navien. It’s our pick for a budget-conscious whole-home gas upgrade.
4. Stiebel Eltron Tempra 36 Plus — Best Whole-Home Electric
Stiebel Eltron Tempra 36 Plus Electric Tankless
- 36 kW of power delivers up to ~7 GPM in warm and moderate climates.
- Advanced Flow Control automatically throttles flow slightly to hold your set temperature instead of running cold.
- ~99% thermal efficiency and no venting — but needs serious 240V service (roughly 150A across multiple breakers).
When there’s no gas line, the Tempra 36 Plus is the best whole-home electric unit we’d buy. Its Advanced Flow Control is the standout: instead of letting output go tepid when demand spikes, it gently reduces flow to keep your water at temperature. Just budget for the electrical work — 36 kW is a big load. See our full electric tankless roundup, the whole Stiebel Eltron Tempra lineup, and the electric vs gas breakdown before committing.
5. EcoSmart ECO 27 — Best Budget Electric
EcoSmart ECO 27 Electric Tankless
- 27 kW self-modulating unit rated up to ~6.6 GPM in warm climates, with a low 0.3 GPM activation flow.
- Compact wall unit with digital temperature control and a lifetime limited warranty (conditions apply).
- Great value for a warm-climate 2-bath home or a sunbelt build.
The EcoSmart ECO 27 gives you real whole-home electric performance for well under $600. Note that its “lifetime” warranty asks for annual maintenance, professional installation, and a water softener on hard water to stay valid — reasonable conditions, but worth knowing. In cold-inlet regions, step up to the 36 kW ECO 36 or a Rheem RTEX-36 — our EcoSmart tankless lineup guide ranks every ECO model by kilowatts, breakers, and climate.
How to choose a tankless water heater
- Fuel: Have a gas line and a big household? Go gas for the higher flow. No gas, warm climate, or a smaller home? Electric is cheaper to buy and install.
- Flow rate (GPM): Size to your peak simultaneous demand — roughly 5.5–7.5 GPM for most homes. Remember every rating is a warm-climate maximum; cold incoming water can cut it in half. Our tankless water heater sizing guide walks through the exact BTU/GPM formula with worked examples.
- Efficiency (UEF): Condensing gas units hit ~0.93–0.97 UEF; non-condensing run ~0.81–0.82 but cost less and need stainless venting. Electric is ~98–99% at the unit.
- Install reality: Gas may need a bigger gas line and venting; high-power electric may need a 150–200A panel and new circuits. Get a quote before you buy the unit. Our tankless water heater venting guide breaks down which units need PVC vs. stainless and the length/clearance limits that decide install cost.
- Recirculation: If you hate waiting for hot water, choose a unit with built-in or add-on recirculation (like the Navien).
- On a well? Untreated well water routinely exceeds every major brand’s published iron and hardness limits, which voids the warranty faster than city water ever would. Our tankless water heater for well water guide covers the sediment/iron/softener stack to install first.
- Torn between the two biggest names? Our Rinnai vs Rheem comparison breaks down the flagship RX199iN vs IKONIC matchup — and the deciding factor if you need electric.
- Want built-in recirculation without buying a second SKU? Our Rinnai vs Navien comparison covers why the NPE-240A2 bundles a pump standard while Rinnai keeps it as a step-up model.
- Buying a Rinnai and want to add recirculation yourself? Most pumps sold at Home Depot are built for tank heaters and say so on the box — see our best recirculating pump for a tankless water heater guide for the on-demand models that actually work.
- Not sure tankless is even the right technology? A heat pump water heater is a different animal — still a tank, but far more efficient. See our heat pump vs tankless water heater comparison before you decide.
- Mounting on an exterior wall instead of a closet or garage? An outdoor-rated unit skips indoor venting entirely. See our best outdoor tankless water heater guide for wall-mount and off-grid picks.
- Outfitting a business instead of a home? Restaurants, salons, and multifamily buildings need cascade-ready, Commercial ENERGY STAR-certified units built for a duty cycle no residential model is warrantied for — see our best commercial tankless water heater guide.
- Thinking about heating a pool or spa with one of these? None of the units on this list are warranty-rated for chemically treated water — see our guide on whether a tankless water heater can heat a pool for the purpose-built alternative that actually works.
The bottom line
For most homes with natural gas, the Rinnai Sensei RX199iN is the tankless water heater to buy: 11.1 GPM, 0.98 UEF condensing efficiency, WiFi, a 15-year heat-exchanger warranty, and a $1,530–$1,725 street price that runs $100–$300 below the comparable Navien. Want instant hot water? The Navien NPE-240A2 adds built-in recirculation. Shopping at retail on a budget? The Rheem Performance Platinum 9.5 GPM delivers. And with no gas line, the Stiebel Eltron Tempra 36 Plus (or the value EcoSmart ECO 27) is the electric pick. Want a brand that just refreshed its whole lineup instead of an established big-three name? Our best Noritz tankless water heater guide covers the new 2026 EZ Series and its 25-year warranty. Considering Bosch? Read our best Bosch tankless water heater guide first — its gas Greentherm line is filed as discontinued on Bosch’s own site, while its electric Tronic 3000 line is current but point-of-use only. Talking to a plumber who recommends Bradford White? Our best Bradford White tankless water heater guide covers the K, L, GR, and GS Series — a trade-channel brand you won’t find at Home Depot, sold through the same wholesalers your contractor already orders from. Want a big-name tank brand’s tankless side instead? Our best A.O. Smith tankless water heater guide covers the Adapt+ flagship’s X3 Scale Prevention Technology and the Signature electric line, both of which — unlike Bradford White — are on Lowe’s and Amazon shelves. Want that same hardware through A.O. Smith’s wholesale-only sibling instead? Our best State tankless water heater guide covers the badge-shared GTS platform sold through plumbing wholesalers, not big-box retail. No natural-gas line? Our best propane tankless water heater roundup covers whole-home and off-grid LP units, and our best RV tankless water heater guide covers drop-in units for campers and vans. Building a tiny house instead? See our best tankless water heater for a tiny house guide for picks sorted by what your electrical panel can actually support. Living in a manufactured or mobile home? Our best tankless water heater for a mobile home guide covers the HUD-approval rule most buyers miss before comparing GPM. Still deciding whether tankless is worth it at all? Read our tankless vs tank guide or our full tankless water heater pros and cons breakdown, and budget the whole job — not just the box — with our tankless water heater cost breakdown. Whichever unit you land on, plan the one recurring job that keeps it alive — our tankless water heater descaling guide covers the flush kits worth buying and the brand rules that differ sharply (Rinnai bans chemical descalers outright), and our full maintenance checklist covers the other three recurring tasks manufacturers require beyond descaling. If your unit ever throws a blinking code, our tankless water heater error codes guide decodes what Rinnai, Navien, and Rheem’s codes actually mean before you call a tech. Before you compare heat-exchanger years across brands, our tankless water heater warranty guide breaks down what Rinnai, Rheem, Navien, and EcoSmart actually cover — and the recirculating-pump condition that quietly cuts most of those warranties in half. And before you order the unit and install parts online, see whether Amazon Prime is worth it for a tankless install. Timing the purchase itself? Our tankless water heater deals guide covers when prices actually drop and which rebates stack on top of a sale price. And don’t forget the vent kit — it’s sold separately from the heater and isn’t interchangeable across brands; our best tankless water heater vent kit guide sorts the OEM PVC options by brand and flags the stainless kit non-condensing units need.