Best Tankless Water Heaters (2026)
A tankless heater that is sized wrong is worse than the tank it replaced. This guide starts with sizing by temperature rise, which is the step most buyers skip, then compares the units that are widely installed and supported in North America.
Navien NPE-240A2
- Built-in buffer tank and recirculation pump (ComfortFlow) — not an accessory
- 15-year heat exchanger warranty, the longest widely available
- 0.95 UEF
The ranked top 4
Navien NPE-240A2
Best for homes with a long run to the far bathroom
The unit that addresses the cold-water sandwich in the box rather than as an add-on, with the longest heat exchanger warranty in the category.
Rinnai RU199iN
Best for a typical family of four
The unit most installers reach for when the brief is simply 'reliable, well supported, correctly sized'.
Rheem Prestige condensing series
Best for buyers weighing efficiency against price
Condensing performance and solid warranty terms without the top-of-market price.
Rheem RTEX-18 (electric)
Best where there is no gas supply and the climate is mild
A sensible electric answer in warm-inlet regions — and the wrong answer almost everywhere cold.
Compared
| Pick | Best for | Flow | Efficiency | Warranty |
|---|---|---|---|---|
| Navien NPE-240A2 | Best for homes with a long run to the far bathroom | 5.6 GPM at 67°F rise | 0.95 UEF | 15 yr heat exchanger / 5 yr parts / 1 yr labour |
| Rinnai RU199iN | Best for a typical family of four | About 11 GPM (moderate climate) | 0.96 UEF | See manufacturer |
| Rheem Prestige condensing series | Best for buyers weighing efficiency against price | 9.5 GPM at 35°F rise | 0.94 UEF | See manufacturer |
| Rheem RTEX-18 (electric) | Best where there is no gas supply and the climate is mild | About 3.5 GPM at 35°F rise | 0.99 UEF | See manufacturer |
How we reviewed this
Size it by temperature rise, not by GPM
Every flow figure in this category is quoted at a stated temperature rise, and the quoted rise is usually a generous one. A unit advertised at 9.5 GPM at a 35°F rise will deliver far less in a northern winter, where incoming water can arrive near 40°F and you are asking for a 70°F rise or more. Work out your own inlet temperature and your target, and read every spec at your rise.
What this guide is based on
Published manufacturer specifications, warranty documents and parts availability, plus general trade experience of how this equipment behaves once installed. We have not bench-tested these units and we publish no numeric score, because a score implies a measurement we did not take.
What we weigh
- - Delivered flow at a realistic rise, not the headline number.
- - Warranty on the heat exchanger, which is the expensive part. Length varies widely.
- - Cold-water sandwich behaviour — whether recirculation is built in or an extra.
- - Install reality — venting, condensate, gas line sizing, or electrical capacity. These often cost more than the difference between two units.
- - Who services it locally. A well-supported unit beats a marginally better one nobody nearby will touch.
Links
Manufacturer reference links, not affiliate links — we are not currently in these programmes. If that changes the link will be labelled and the disclosure at the top of this page still applies. Specifications are as published at the date shown.
Why Trust Our Recommendations
FAQ
What is the cold-water sandwich?
A short slug of cold water arriving mid-shower, usually when hot water is turned off and back on quickly. The heater takes a moment to fire and the water already in the pipe passes through unheated. Units with a built-in buffer tank and recirculation pump largely remove it; on others it can be reduced with an external recirculation loop, which adds cost.
Will a tankless heater save me money?
Usually on energy, and rarely enough to pay back the installation quickly on its own. The stronger reasons are endless hot water, a much smaller footprint, and a longer service life than a tank. If payback is the only reason you are considering it, check the numbers for your own household before committing.
Electric or gas?
Gas for most whole-house applications, because electric units struggle to deliver enough flow once the required temperature rise is large. Electric makes sense where there is no gas supply, the inlet water is warm, and the electrical service can carry it — and the panel upgrade should be priced before you decide.
Have you tested these yourself?
No, and we will not imply otherwise. This is a specification, warranty and installability comparison informed by trade experience with this class of equipment. Any page where we have hands-on time will say precisely what that involved.
About the reviewer
Nelo Tested Trade-informed — see who publishes Nelo Tested and how we review.