Rinnai Vs Navien: Which Tankless Water Heaters Is Better?

Whenever I walk into a home with natural gas or propane, I recommend installing a tankless water heater. They’re quickly becoming the most sought-after water heaters next to hybrid-electric units, and can provide “endless hot water.”

Two brands – Rinnai and Navien – are now the most common choices among plumbers (myself included). While Rinnai has a slight edge over Navien with regard to reliability, Naviens aren’t bad units. Both will last a long time with regular maintenance.

In this article, we’ll provide an overview of two models we install: Rinnai’s RUR199iN and Navien’s NPE-240A2. Both possess ¾” natural gas connections, condensing technology, and require direct air intake and exhaust connections.

One point to clarify: tankless systems are almost always wall-mounted. In fact, I’ve never seen a tankless that isn’t. An installer sets a couple of two-by-fours to your basement wall, drills a sheet of plywood to the two-by-fours, and then mounts the water heater. Keep this in mind when you’re picking one out.

Delivering 11 gallons per minute of flow, the RUR199iN is capable of serving a home with three to six fixtures running simultaneously. It weighs 73 lbs, and is about 2’7” high. Big Frog Supply listed the RUR199iN at $2,178.75 as of June 2021.

As outlined in our article comparing A.O. Smith and Bradford White’s water heaters, the Department of Energy (DoE) developed the UEF to assess water heater efficiency. The higher the UEF, the lower the energy costs.

A .93 UEF is one of the best ratings you’ll get from a gas-fired water heater, whether we’re talking tankless or tank-type models. The RUR199iN’s Energy Guide sticker estimates a yearly energy cost of about $201 – making it more efficient than similar tankless water heaters.

The RUR199iN’s reliability lies in the warranties themselves. Many manufacturers won’t warranty their heat exchangers for more than 12 years, while Rinnai has a 15-year warranty.

At my company, we typically offer the Rinnai as the “best” option out of the three we install (Rinnai, Bosch, and Navien). We’ve had fewer service calls on these models, particularly on the heat exchanger’s flame sensor.

One thing to note: the water tappings located at the bottom of the system don’t wobble when cranking on brass fittings. It’s a little detail that attests to the Japanese brand’s quality manufacturing and engineering. I don’t have to worry about breaking an internal connection and ordering a part right off the bat.

Homeowners appear happy with Rinnai’s water heaters as well. Avid Ratings, which offers customer experience solutions, aggregated feedback from 5,000 Rinnai customers who had submitted warranty registrations. The manufacturer earned 4.4 out of 5 stars for satisfaction.

With regard to performance, the Rinnai is on par with the Navien. Both models will produce the “cold water sandwich” many customers complain about from time-to-time. This is an important detail to remember.

Think about it: the water heater isn’t running until you turn on the hot side of a fixture. The sensors in the water heater will register water flowing from its hot outlet, and then commence the combustion process. If you keep the fixtures running, then you’ll get the “endless hot water” these systems are famed for delivering.

This is where the little details matter. One thing I like about the Rinnai is the location of its condensate drain. It’s located to the left of the cold inlet, hot outlet, and gas inlet connections. It’s a small design feature that makes installation go a lot smoother.

Another nice convenience is that the temperature and pressure (T+P) relief valve has its own port. Many tankless models place the T+P on a female adapter located on the hot inlet’s isolation valve. Rinnai’s approach makes servicing a tad more secure, as you don’t have to worry about moving the hot inlet’s tapping.

The only real issue I’ve seen with the Navien is that the flame sensors on the heat exchanger fail prematurely. I’ve replaced several in the six months I’ve been working as a service plumber.

Other than that, the NPE-240A2 isn’t poorly built by any means. The water tappings move slightly when threading on isolation valves, but that’s the only real concern. One thing’s for sure: the stainless steel heat exchanger increases the unit’s durability against hard water.

My only gripe with the NPE-240A2 is that the condensate drain is located behind the gas inlet. It reduces the amount of space I have to work with, especially if I need to put an acid neutralizer on the system.

Other than that, the NPE-240A2 is on par with the Rinnai. I’d say the Rinnai is marginally faster to install. The big deciding factor is the house in which I’m working. Is the gas connection 20 feet away? Do I need to drill through a 100-year-old 8-inch by 8-inch beam for the vents? These are things most plumbers think about.

Overall, you’re looking at two fine systems. The NPE-240A2 is generally more affordable, but the Rinnai’s quality is a tad higher. Your go-to plumber may have a different opinion, though. Listen to them!

From there, a control board (essentially, a small computer) monitors the flame rods, fan motor frequency, hot water temperature, water flow rate, and set temperature. It will open more solenoid valves as water demand increases, and close solenoid valves as demand decreases.

One thing to note: Most condensing boilers have a secondary heat exchanger to pre-heat the water before it enters the primary heat exchanger. The secondary heat exchanger facilitates this heat transfer by using the warm condensate from the water heater’s flue gas vent.

The control board shuts down the tankless system whenever you turn off the hot side of your fixtures. If you don’t need hot water at the moment, there’s no need for the water heater to run.

This is what makes tankless water heaters much more efficient than tank-type alternatives. The flame on a tank needs to heat up at least 50 gallons of water, so the combustion process lasts much longer.