APUS tankless water heater review: 190,000 BTU at half the price of a Rinnai

Before anything else: this is a gas appliance. APUS sells its tankless heaters in propane and natural gas trims, indoor and outdoor. A significant share of people searching for "APUS tankless" are shopping electric units and are in the wrong aisle — if that is you, the electrical requirements for electric tankless units explains why the electric equivalent of this capacity needs 112 amps and three double-pole breakers.

With that settled: for around $700, this is more burner than anything else at the price.

The flow rate is real, and it is conditional#

Every tankless water heater is sold on a single flow number, and that number is measured at the smallest temperature rise the manufacturer can justify. It is not dishonest — a heater genuinely does deliver 8.1 GPM when it only has to warm the water a little. It is just useless for sizing unless you know your own conditions.

Here is the same unit's output across the temperature rises people actually have.

The mechanism is simple arithmetic. A BTU raises one pound of water one degree Fahrenheit. Water weighs 8.34 lb per gallon. So:

GPM = BTU output ÷ (temperature rise × 8.34 × 60)

At 190,000 BTU input and roughly 82% thermal efficiency, that is about 155,800 BTU of usable output. Divide by a 70 °F rise and you get 4.4 to 4.9 GPM depending on how you account for standby losses. Divide by a 40 °F rise and you are at 7.6.

Groundwater temperature is what sets your rise, and it varies from about 75 °F in south Florida to 42 °F across the northern tier. That is why a heater sized correctly in Georgia is undersized in Michigan, and why household size is the wrong first question. Our our tankless sizing calculator does this arithmetic with a regional groundwater dataset built in, and how to size a tankless water heater explains the method.

What the outdoor mount saves, and what it costs#

Mounting outdoors is the single biggest reason this unit lands where it does on price.

Indoor gas tankless heaters need venting. Category III stainless flue for a non-condensing unit runs $40 to $70 a foot in materials, and a typical run with a wall penetration and a termination lands somewhere between $600 and $1,500 installed. Concentric direct-vent kits are not cheaper. Skip all of that and you have removed a large, unavoidable line item.

The saving is real. The cost is that you have put a water-filled appliance outside.

Freeze protection on this unit is electric. There is a heating element and a control board that keeps the heat exchanger above freezing, and it works well — while the unit has power. The failure scenario is specific and worth stating plainly: a winter storm knocks out power for eighteen hours, the temperature sits at 20 °F, the freeze protection is off, and the water inside the exchanger freezes and expands. Copper does not survive that, and a heat exchanger burst by freezing is excluded from essentially every manufacturer's warranty including this one.

Two mitigations, and you should pick one before installing:

• A small UPS. The unit draws 120 V and the freeze protection element is modest. A consumer UPS will hold it for several hours, which covers most outages.
• A documented drain-down. Isolation valves on the hot and cold sides plus a drain port, and a written procedure taped inside the cover. It takes ten minutes and it has to be done in the dark, in the cold, during the storm.

In zone 6 and warmer this is a manageable risk. In zone 4 and colder we would install this indoors with the venting cost, or buy a different product.

Propane consumption is the running cost nobody quotes#

190,000 BTU is a lot of burner, and propane carries about 91,500 BTU per gallon. At full fire the unit consumes roughly 2.1 gallons per hour.

That number only matters in the context of your tank.

Real households do not run a water heater at full fire continuously — actual duty cycle for a family of four is perhaps 45 to 90 minutes a day of equivalent full-fire time. But the tank sizing conversation is one buyers routinely have after the heater arrives, and a tank installation is a separate project with its own permit, setback rules and lead time.

If you are on natural gas rather than propane, none of this applies and the running-cost comparison against a tank heater is much more favourable — that arithmetic is in the ten-year cost comparison against a tank.

Where it sits against Rinnai and Rheem#

The two units people cross-shop are the Rinnai RU199iN and the Rheem RTGH-95DVLN.

Two things stand out. The APUS is not condensing, which costs it efficiency — condensing units recover heat from the flue gas and run in the low 90s for efficiency against the low 80s here. Over a decade of propane that gap is real money, and it partly offsets the purchase saving.

And the warranty gap is wide. Five years against twelve on the heat exchanger is the clearest statement either manufacturer makes about expected service life.

What APUS wins on is price per GPM and the absence of a venting bill. If the install is straightforward and you have a plumber willing to work on an unfamiliar brand, that is a strong position. The gas-versus-electric version of this comparison is in APUS against EcoSmart.

Who should not buy this#

• Anyone shopping for an electric tankless heater. Different product, different install, different failure modes. Start with breaker and wire sizing for tankless heaters instead.
• Anyone in zone 4 or colder installing outdoors. The freeze-protection dependency on mains power is a real exposure in a region where winter outages happen.
• Apartments and condos. Outdoor mounting is rarely permitted, and 8.1 GPM is enormous over-capacity for a one-bathroom dwelling.
• Anyone whose propane supply is cylinders. Whole-home service on 100 lb bottles means changing them constantly. Sort the tank before the heater.
• Buyers who need same-week parts. There is no plumbing-supply channel for APUS components. A failed control board is a shipment, not a trip to the counter.

The verdict#

7.8. The hardware is genuinely competitive and the price is not a trick — you are getting a large burner, real safety interlocks, and connectivity that costs extra elsewhere. What you are not getting is condensing efficiency, a twelve-year exchanger warranty, or a service network, and those are the things that separate a $700 heater from a $1,400 one.

For a mild-climate propane installation where the venting saving is real and a competent local plumber is available, it is a strong buy. For a northern outdoor install, or for a household that cannot tolerate downtime, the extra $700 for a Rinnai buys things you will eventually want.

Size it before you buy it — that is the step that decides whether any of this matters. the GPM calculator takes about a minute.