Quick Answer: The best outdoor tankless water heater for most whole-home installs is the Rinnai V65eN — a 150,000 BTU natural gas unit rated up to 6.5 GPM (warm inlet), 0.79 UEF, and a 12-year heat exchanger warranty, mounted entirely on an exterior wall with no indoor venting required. Smaller homes can save money with the compact Rinnai V53DeN (5.3 GPM). Homeowners who want Wi-Fi monitoring should look at the Rheem ECO200XELN-3 (9.5 GPM). For sheds, cabins, or camp showers with no electrical hookup, the Eccotemp L10 runs on batteries alone. Every GPM figure below assumes a warm winter-mild inlet — cold groundwater lowers real flow, same as any tankless unit.
An outdoor tankless water heater mounts on an exterior wall instead of inside a closet, garage, or utility room. Because the whole unit — burner, heat exchanger, and exhaust — sits outside, combustion gases vent directly to open air, so you skip the PVC or stainless venting kit an indoor unit needs. According to Rinnai’s own outdoor V-series spec sheet, the V65eN delivers the same 150,000 BTU output and 6.5 GPM warm-inlet flow as its indoor V65iN sibling, with the only real difference being the weatherproof cabinet and the venting you don’t have to install. We compared the leading outdoor-rated models on flow rate, BTU, efficiency, and price so you can pick the right one for your home, cabin, or outdoor kitchen.
Our top picks at a glance
| Model | Best for | BTU | Max Flow (warm inlet) | UEF | Power | Price |
|---|---|---|---|---|---|---|
| Rinnai V65eN | Best overall | 150,000 | 6.5 GPM | 0.79 | 120V, 4A | ~$757 |
| Rinnai V53DeN | Best compact / budget | 120,000 | 5.3 GPM | 0.81 | 120V | ~$617 |
| Rheem ECO200XELN-3 | Best Wi-Fi / high-flow | 199,900 | 9.5 GPM | 0.82 | 120V | ~$1,103 |
| Eccotemp L10 | Best off-grid / portable | 75,000 | 3.0 GPM | — | 2 D-cell batteries | ~$289–360 |
By the numbers
- 150,000 BTU max input, 0.26–6.5 GPM flow range, 0.79 UEF on the Rinnai V65eN — ENERGY STAR qualified, per Rinnai’s own product spec sheet. — Rinnai
- 9.5 GPM at a 35°F temperature rise, 199,900 BTU, 0.82 UEF on the Rheem ECO200XELN-3, enough for up to three bathrooms running at once per Rheem’s spec. — Rheem
- 75,000 BTU, 3.0 GPM, 20–80 PSI operating range on the Eccotemp L10, which lights on 2 D-cell batteries with no electrical hookup at all. — Eccotemp
- 12-year heat exchanger warranty on the Rinnai V65eN and V53DeN, well above the 1-year label warranty typical of portable propane units. — Rinnai
1. Rinnai V65eN — Best Overall
Rinnai V65eN Outdoor Tankless Water Heater
- 150,000 BTU non-condensing burner rated up to 6.5 GPM warm-inlet flow — enough for a 2–3 bathroom home.
- Weatherproof outdoor cabinet mounts directly on an exterior wall; no indoor venting kit needed.
- Digital Electronic Water Control lets you set outlet temperature precisely; 12-yr heat exchanger, 5-yr parts, 1-yr labor warranty.
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The V65eN is the outdoor sibling of Rinnai’s popular V65iN, and it’s the pick we’d make for most whole-home outdoor installs. Its 150,000 BTU burner and 6.5 GPM warm-inlet flow cover a typical 2–3 bathroom household, and because the entire unit lives outside, you avoid the PVC/CPVC or stainless venting kit an indoor non-condensing unit requires — a real savings in materials and labor. The trade-off versus Rinnai’s premium condensing indoor models is efficiency: at 0.79 UEF it runs several points below a 0.95+ UEF condensing unit, so expect slightly higher gas bills in exchange for the simpler, cheaper install. Rinnai’s outdoor V-series includes freeze protection to roughly -30°F as long as the unit stays powered.
2. Rinnai V53DeN — Best Compact / Budget
Rinnai V53DeN Outdoor Tankless Water Heater
- 120,000 BTU rated up to 5.3 GPM warm-inlet flow — sized right for a smaller 1–2 bathroom home or a guest house.
- Digital temperature control adjustable from 115–140°F; same 12-yr heat exchanger warranty as the larger V65eN.
- Requires a 120V electrical connection, like every wall-mounted model on this list — it isn't a battery unit.
If a full 150,000 BTU unit is overkill for your home, the V53DeN gives you the same outdoor-mount, no-venting convenience at a smaller size and a lower price. 5.3 GPM comfortably covers one shower running alongside a sink or dishwasher, which is plenty for a 1–2 bathroom house, small rental, or accessory dwelling unit. It carries the same 12-year heat exchanger warranty as its bigger sibling, so you aren’t giving up long-term coverage to save money upfront. Note that despite the compact size, it still needs a 120V outlet nearby for ignition and controls.
3. Rheem ECO200XELN-3 — Best Wi-Fi / High-Flow
Rheem Performance Plus ECO200XELN-3 Outdoor Tankless Water Heater
- 199,900 BTU, the largest burner in this roundup, rated 9.5 GPM at a 35°F temperature rise per Rheem's spec — enough for up to 3 bathrooms at once.
- Built-in Wi-Fi lets you monitor and adjust from the Rheem EcoNet app, a feature the Rinnai V-series outdoor models don't offer.
- Sleek weatherproof outdoor cabinet; no interior venting required, same as the Rinnai models above.
For larger homes or anyone who wants app-based control, the Rheem ECO200XELN-3 is the strongest outdoor pick on flow alone — its 9.5 GPM rating at a 35°F rise beats both Rinnai outdoor units here, and Rheem’s EcoNet Wi-Fi module (absent from Rinnai’s outdoor V-series) lets you check status and adjust temperature remotely. It costs noticeably more than the Rinnai V65eN, so it’s the right call mainly for bigger households running multiple fixtures simultaneously, or for anyone who specifically wants smart-home integration on an outdoor unit.
4. Eccotemp L10 — Best Off-Grid / Portable
Eccotemp L10 Portable Outdoor Tankless Water Heater
- 75,000 BTU on a standard 20-lb propane tank, delivering up to 3.0 GPM with no 120V hookup at all.
- Battery electronic ignition (2 D-cells) makes it the only unit here suited to sheds, cabins, or camp showers without wired power.
- Automatic safety shut-off if run longer than 20 minutes or tilted past 45°; includes a hose, regulator, and shower head.
Every other unit on this list still needs a 120V outlet outdoors, which isn’t always available at a detached shed, off-grid cabin, or outdoor kitchen. The Eccotemp L10 solves that: it runs entirely on propane and 2 D-cell batteries, so it goes anywhere a garden hose and a propane tank can reach. At 3.0 GPM and 75,000 BTU it’s not sized for a whole house, but it’s plenty for a single outdoor shower, a wash-down station, or a bunkhouse sink. It has no built-in freeze protection, so drain it and bring it indoors once temperatures drop toward freezing.
How to choose an outdoor tankless water heater
- Size by BTU and household need, not just GPM: A 1–2 bathroom home is well served by the 120,000 BTU V53DeN; a 2–3 bathroom home should look at the 150,000 BTU V65eN or larger Rheem ECO200XELN-3.
- Don’t assume “outdoor” means “no electricity”: Every wall-mounted unit in this roundup (Rinnai and Rheem) needs a 120V outlet for ignition and controls. Only the battery-powered Eccotemp L10 skips electricity entirely.
- Weigh the venting savings against efficiency: Outdoor non-condensing units (0.79–0.82 UEF here) skip the venting kit an indoor condensing unit needs, but run a few efficiency points below premium indoor models — a fair trade for many installs, not a free upgrade.
- Plan for freeze protection: Rinnai’s outdoor V-series is rated to roughly -30°F while powered; a power outage during a hard freeze can still cause damage, so cold climates may still want pipe insulation or an enclosure.
- Match the use case: Whole-home outdoor installs want the Rinnai or Rheem wall-mounted models; sheds, cabins, and outdoor kitchens without power are better served by a portable unit like the Eccotemp L10.
The bottom line
For most homeowners installing a whole-home outdoor unit, the Rinnai V65eN is the best outdoor tankless water heater: 150,000 BTU, up to 6.5 GPM, a 12-year heat exchanger warranty, and no indoor venting required. Smaller homes can save money with the compact Rinnai V53DeN, and households that want Wi-Fi monitoring and the highest flow should look at the Rheem ECO200XELN-3. For sheds, cabins, or camp showers with no power hookup, the Eccotemp L10 is the only real option here. Comparing an outdoor unit against RV-specific models? See our best RV tankless water heater guide, or start with our best tankless water heater roundup to compare every fuel type and installation style.