Best Outdoor Tankless Water Heaters (2026)

The RX180iN is a condensing unit with 180,000 BTU of input and a rated 10 GPM, and the same model installs indoors or outdoors thanks to Rinnai's Versa Vent system. It runs on natural gas or propane, which simplifies buying if you are not sure which you will have.

Condensing means the exhaust is cool and the unit is more efficient, but it also produces acidic condensate. Outdoors that is less of a problem, because the drain can run to a safe spot, though in freezing weather the condensate line itself can ice up. Against the Rheem RTG 8.4 GPM it has more flow and higher efficiency, and against the Westinghouse it is much larger.

Ownership includes a yearly descale, a check of the freeze protection and a look at the vent cap. Rinnai's service network is the deepest here, which matters in year eight. If you choose the outdoor option, route the condensate line with a steady downward slope to a drain and consider a heat-traced line or a short run in a cold region, since a frozen condensate line can shut the unit down. Keep the manual and the installer notes together, because the settings for altitude and fuel type are easy to forget in year five.

The RTG 8.4 is a non-condensing outdoor natural gas unit with 180,000 BTU of input, a stated UEF of 0.82 and a rated 8.4 GPM. Because it vents straight out the cabinet, there is no stainless pipe to run, and non-condensing means no condensate drain.

By the standard formula, 180,000 BTU at 0.82 gives about 148,000 BTU of useful heat, so roughly 4.2 GPM at a 70F rise and 7.4 GPM at a 40F rise. That makes the 8.4 headline a best case at a rise near 35F. Compared with the RTG 7.0 it adds about 12 percent more input, and compared with the Rinnai it is simpler but less efficient.

Ownership is routine: a yearly descale, an inlet screen check and a look at the weather shield. Keep the clearances the manual lists around the cabinet. Because the cabinet sits in the weather, inspect the gasket and the vent cap each autumn for cracks, and wire the electrical supply through a weatherproof, GFCI-protected outlet rather than a cord looped across the ground.

The RTG 7.0 outdoor model is the smaller sibling at 160,000 BTU and 7.0 GPM, with the same 0.82 UEF and no vent run. The listing says it saves up to 34 percent compared with a standard tank, which is a manufacturer comparison.

Its useful heat is about 131,000 BTU, so roughly 3.7 GPM at a 70F rise and 6.5 GPM at a 40F rise. That suits a two to three bathroom home in a mild climate. Compared with the 8.4 GPM model it has about 11 percent less input and a lower price, and compared with the Westinghouse it adds about a third more capacity.

Ownership centers on the same descaling and screen care. Mount it with the manual's clearances, keep snow and leaves away from the cabinet and make sure the gas line is sized for 160,000 BTU. It also suits a home that already has a half-inch gas line near the planned wall, since the lower input is easier to supply than the 180,000 BTU models.

Westinghouse's outdoor unit lists 120,000 BTU and 5.1 GPM, with self-modulating technology that adjusts gas and water flow to hold the setpoint within one degree. It is designed for outdoor wall mounting and whole-house use.

The useful heat at roughly 0.8 efficiency is about 96,000 BTU, so about 2.7 GPM at a 70F rise and 4.8 GPM at a 40F rise. That suits two to three fixtures in a mild climate. Against the Rheem RTG 7.0 it has about 75 percent of the input, and against the Orbek it has a similar rating and a widely known brand name.

Ownership is the usual descale and inlet screen care, plus keeping the cabinet clear of debris. Confirm the freeze-protection behavior in the manual. In snow country, mount it above the expected snow line and keep a clear path to the cabinet, because a drifted cabinet is both a freezing risk and a service headache.

Orbek's unit lists 120,000 BTU and 5.1 GPM, CSA certification, plus or minus 1F stability and WiFi control through its app and voice assistants. It is designed for both indoor and outdoor installation.

The flexibility is the point: you can choose outdoor mounting now and move indoors later, or use the same model across properties. The tradeoff is a newer brand with less service depth. Compared with the Westinghouse it adds CSA certification and an app, and compared with the Rheem units it has less input and no stated UEF.

Ownership is the usual descale, screen and clearance care. Treat the app as a convenience, and make sure the unit works without it. If you pick it, verify in the manual which of its settings assume an indoor install, because outdoor use may change the venting and the freeze protection requirements.

Ranein's outdoor unit lists 190,000 BTU, 8.5 GPM for four to six water points and an under-mounted fan that the listing says prevents smoke backflow. It is a natural gas model built for outdoor mounting.

By the formula, 190,000 BTU at about 0.8 efficiency gives roughly 4.3 GPM at a 70F rise and 7.6 GPM at a 40F rise, so the 8.5 GPM headline needs a rise near 36F. Compared with the Rheem 8.4 it has more input and no stated UEF, and compared with the Rinnai it is non-condensing and less costly.

Ownership is the usual care, with an extra check of the power supply to the fan. Confirm the warranty and parts availability, since the brand is newer. Walk the planned location with the installer before you order, because a 190,000 BTU unit needs a sturdy wall, a larger gas line and open space around the cabinet.