New to this? Start with our complete guide: Tank vs. Tankless: Which Is Worth It?.
Already own one and it has gone lukewarm? That is almost always scale — see how to descale a tankless water heater.
Quick answer — the best tankless water heater for most homes
For most homes on natural gas, buy the Rinnai RU160iN: an ENERGY STAR condensing unit with a Uniform Energy Factor of 0.97 and up to 9 GPM — enough for a typical 2–3 bathroom home — backed by a 15-year heat-exchanger warranty, and it is the most widely installed tankless brand, so any plumber can service it. Want a second gas option? The Rheem RTGH-90DVLN-3 (180,000 BTU/hr maximum input, up to 9.0 GPM at a 35°F rise, condensing, 15-year heat-exchanger warranty on Rheem’s RTGH series spec sheet) is the value pick. All-electric or no gas line? The EcoSmart ECOS 27 (240V, 27 kW, 112.5 amps, self-modulating, no venting) covers a warm-climate home — but it needs serious electrical capacity (realistically three 40A breakers on a 200A panel) and its flow falls to roughly 2.7 GPM once the incoming water is cold.
Before you buy: go with whatever fuel your home already uses (switching fuel types is expensive), size the GPM to your climate and simultaneous-use needs (cold climates favor 9–11 GPM gas units), and have gas units professionally installed — improper venting or gas sizing is dangerous and voids warranties. Budgeting the job? See our cost to install a tankless water heater.
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Tankless water heaters give you endless hot water and cut standby energy losses, but the wrong unit means lukewarm showers or a huge install bill. The two things that matter: gas vs. electric (based on your home’s existing service) and flow rate (GPM) sized to your climate and number of bathrooms.
Here are the three I’d install, covering most homes. A quick note: tankless installs often need gas-line or electrical upgrades and proper venting — budget for a pro install on gas units.
| Pick | Model | Fuel | Max output | Max flow | Efficiency | Warranty |
|---|---|---|---|---|---|---|
| Best Gas (Overall) | Rinnai RU160iN | Natural gas | Condensing, indoor | up to 9 GPM | 0.97 UEF (ENERGY STAR) | 15-yr HX / 5-yr parts |
| Best Value Gas | Rheem RTGH-90DVLN-3 | Natural gas | 180,000 BTU/hr | 0.4–9.0 GPM | Condensing | 15-yr HX / 5-yr parts |
| Best Electric | EcoSmart ECOS 27 | Electric, 240V | 27 kW / 112.5 A | 2.7–6.6 GPM | 96% thermal (mfr.) | 5-yr leaks / 1-yr parts |
Before you buy, see what it costs to put one in — our tankless installation cost breakdown covers the unit, gas, and venting.
Rinnai RU160iN — An ENERGY STAR condensing unit (0.97 UEF) with up to 9 GPM — enough for a typical 2–3 bathroom home, and the most widely installed tankless brand any plumber can service.
Check the Rinnai RU160iN on Amazon →Rinnai RU160iN Condensing Tankless
Natural gas · indoor · up to 9 GPM · 0.97 UEF, ENERGY STAR qualified (condensing) · 15-yr heat exchanger / 5-yr parts / 1-yr labor
For most homes on natural gas, the RU160iN is the one I’d hang on the wall. It is a condensing unit with a Uniform Energy Factor of 0.97 — the highest verified efficiency of the three — and up to 9 GPM, which Rinnai rates as enough to feed up to six fixtures. That covers a typical 2–3 bathroom home. It also ships Circ-Logic ready, so you can pair an external recirculation pump and stop waiting at the far tap. And Rinnai is the most widely installed tankless brand in the country, which matters more than any spec on the day it needs a part.
Straight talk on sizing: if you have four bathrooms and cold northern inlet water, 9 GPM is not enough and you want Rinnai’s 199-series instead. That model has been in and out of stock on Amazon for months, so check a plumbing supplier for it rather than waiting on a listing to come back.
- 0.97 UEF, ENERGY STAR qualified — the highest verified efficiency of the three
- Up to 9 GPM, rated to supply up to six fixtures at once
- Circ-Logic recirculation support for faster hot water at the tap
- Most widely installed tankless brand — any plumber can service it
- 9 GPM tops out around a 2–3 bathroom home; big cold-climate houses need the 199-series
- Condensing design makes acidic condensate that needs a drain
- Parts and labor coverage runs out well before the 15-year heat-exchanger term
Who it’s for: A gas home that wants the highest efficiency and the unit any plumber can service — and is sized at three bathrooms or fewer.
Rheem RTGH-90DVLN-3 Condensing
Natural gas · indoor · 180,000 BTU/hr maximum input · up to 9.0 GPM at a 35°F rise · condensing · 15-yr heat exchanger / 5-yr parts / 1-yr labor
The RTGH-90 is the value play, and it lands right beside the Rinnai on flow. Rheem’s RTGH series specification sheet (form TK-RTGH SERIES REV. 1) rates it at 180,000 BTU/hr maximum gas input and 9.0 GPM at a 35°F temperature rise, and sizes that at three to four bathrooms. Turndown is the underrated part: the same sheet lists a 0.4 GPM minimum activation flow and a 0.26 GPM minimum continuous flow, which is what keeps a slow bathroom tap from going cold on you. Temperature adjusts from 100 to 140°F, the heat exchanger is copper on the primary and stainless steel on the secondary, and Rheem lists half-inch gas line compatibility up to 24 feet, subject to local code — on a retrofit that is often the difference between repiping and not.
- 180,000 BTU/hr maximum input and 9.0 GPM at a 35°F rise — Rheem sizes it for three to four bathrooms
- Activates at 0.4 GPM and holds a 0.26 GPM continuous flow, so low-flow taps still hold temperature
- Half-inch gas line compatibility up to 24 ft, subject to local code — often saves a repipe on a retrofit
- Condensing condensate still needs a drain; Rheem lists the condensate neutralizer as an optional accessory
- Cold inlet water cuts the flow hard — Rheem’s own ground-water zone table puts this model at 4.2 GPM where incoming water is 37°F
- Parts and labor coverage — 5 years and 1 year — runs out well before the 15-year heat-exchanger term
Who it’s for: Most gas homes — it matches the Rinnai’s flow ceiling, Rheem sizes it for three to four bathrooms, and it is the easier of the two to find in stock.
EcoSmart ECOS 27 Electric Tankless
Electric (240V) · 27 kW · 112.5 amps · 2.7–6.6 GPM depending on inlet temperature · 96% thermal efficiency (manufacturer) · 5-yr limited on leaks / 1-yr parts · no venting or gas
For all-electric homes, the ECOS 27 is the one to look at. The 27 kW element bank self-modulates — it only draws the power the current demand calls for — and EcoSmart holds output within a degree of the set temperature. It is 19 by 9¼ by 4¼ inches, so it mounts almost anywhere a tank never would, with no flue and no gas line to run.
The honest caveat is the electrical service. 112.5 amps at 240V is a genuinely large load — in practice three 40-amp circuits and a 200-amp panel. If your panel is older or already full, the upgrade can cost more than the heater, and that is the line most people find out about after the unit arrives. Get an electrician to look at the panel before you buy.
- No combustion, no venting, no gas line — simplest install footprint
- Self-modulating; draws only the power demanded and holds within a degree of setpoint
- 19 x 9.25 x 4.25 inches — mounts on a wall or at the point of use
- 112.5 amps at 240V means roughly three 40A breakers and a 200A panel — older services often need an upgrade first
- Flow falls to about 2.7 GPM once the incoming water is cold, versus 6.6 GPM warm
- Warranty is 5 years on leaks and only 1 year on parts — far shorter than the gas picks’ heat-exchanger terms
Who it’s for: All-electric or no-gas homes with a 200A panel in a warmer climate — check your panel and inlet temperature first.
What the Efficiency Numbers Actually Say
Tankless gets sold on the promise of endless hot water, but the case that holds up under scrutiny is the efficiency one, and it comes with a condition attached.
The U.S. Department of Energy puts tankless units at 24–34% more energy efficient than a storage tank — but specifically for homes using 41 gallons or less of hot water a day. Above that, the advantage narrows sharply. The DOE also puts typical tankless service life at more than 20 years, against 10–15 years for a storage tank. (DOE Energy Saver, archived June 2026)
Read those two together and the real argument emerges. A tankless unit costs more up front and more to install, and it pays that back over a run that is roughly twice as long — provided your household actually sits in the low-usage band the efficiency figure depends on. A family of five running back-to-back showers and laundry is not that household.
So the question to settle before shopping is not which unit is best. It is how much hot water you actually use. The side-by-side is in tank vs tankless, and it is worth ten minutes before spending four figures.
How to Choose the Right Tankless Water Heater
- Decide gas vs. electric based on your existing service — switching fuel types is expensive.
- Add up your peak simultaneous hot-water flow (e.g., two showers plus a sink is roughly 5–6 GPM).
- Factor your climate: colder incoming water needs a higher-GPM unit to hit the same output temperature. Cold climates favor 9–11 GPM gas units.
- For gas, confirm your gas line and venting can support the unit (condensing units use cheaper PVC venting); for electric, confirm panel capacity.
- Have gas units professionally installed — improper venting or gas sizing is dangerous and voids warranties.
FAQ
Gas or electric tankless water heater?
Go with whatever fuel your home already uses — converting is costly. Gas units deliver higher flow rates for whole-home use in any climate but need proper venting and gas sizing. Electric units are simpler to install and great for warm climates or smaller homes, but high-output models demand significant electrical panel capacity.
What size tankless water heater do I need?
Add up the GPM of fixtures you’d run at once (a shower is about 2–2.5 GPM, a sink about 1 GPM) and match a unit that exceeds that at your climate’s temperature rise. Cold climates need higher GPM because incoming water is colder. Most 2–3 bath homes want a 9–11 GPM gas unit.
Are tankless water heaters worth it?
For most homes, yes — endless hot water, lower standby energy loss, a smaller footprint, and a longer lifespan (often 20 years vs. 10–12 for a tank). The trade-off is a higher upfront cost and sometimes gas or electric upgrades at install. Over the unit’s life, the energy savings and longevity usually pay off.
Bottom Line
For gas homes, the Rinnai RU160iN is the do-it-right choice, with the Rheem RTGH-90DVLN-3 as the value pick for most families. All-electric in a warm climate? The EcoSmart ECOS 27, once an electrician has signed off on your panel. Size to your peak flow and climate, match your existing fuel, and have gas units installed by a pro. If you need more than about 9 GPM, none of these three is your unit — that is a 199,000 BTU-class gas heater, and you will have better luck at a plumbing supplier than on Amazon.
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