Cold inlet water and the winter rise
Metro Vancouver's water comes from mountain reservoirs, and in winter the incoming supply can be below 8 °C. To deliver 49 °C at a shower, the unit must raise the water by roughly 40 °C (72 °F). Tankless capacity is a flow rate at a temperature rise, so the colder the inlet, the lower the flow the unit can hold at a given outlet temperature.
This is not a fault and not a loss of efficiency; the unit is still condensing and still rated UEF 0.95. It is simply that a fixed heat input spread over a larger temperature rise produces less hot water. The honest number for a winter sizing conversation is the flow at the rise the home actually sees.
Reading flow at rise
Navien publishes the NPE-240A2's flow at three rises: 11.2 GPM (42.4 L/min) at a 35 °F rise, 8.7 GPM (32.9 L/min) at 45 °F, and 5.6 GPM (21.2 L/min) at 67 °F. A Metro Vancouver winter rise sits in the upper part of that range, so the 5.6 GPM figure is the one to plan against, not the 11.2 GPM headline.
Rinnai publishes the RU199iN as a rated flow range of 0.26 to 9.8 GPM with an 11 GPM maximum after a parameter change, but it does not state the temperature rise behind those numbers and its flow curves apply only to inlet water at or below 21 °C. That makes the published curve, not the headline, the figure a sizing assessment uses.
Simultaneous demand in winter
A shower-class fixture draws about 7.5 to 9.5 L/min (2 to 2.5 GPM). Two showers at once need roughly 17 L/min (4.5 GPM) at a 40 °C rise, which is close to the winter-class output of a single 199,000 BTU/h unit. Three simultaneous fixtures in January can exceed one unit.
FortisBC notes that some tankless units may support only one demand for hot water at a time and that a buffer tank can be added to reduce delays. The honest options for a busy household are to accept that the third fixture waits, to add a buffer tank, or to consider a second unit; the choice is made from measured demand rather than bedroom count.
Freeze protection and power
A condensing tankless unit sits on an exterior wall with a vent to the outdoors, so it has freeze protection for its internal water. The RU199iN draws 148 W when freeze protection is active, against 84 W in normal operation, and it needs 120 V power to run its fan, controls and protection. If the power fails, the unit stops and has no hot water, unlike an atmospheric tank.
The freeze protection protects the unit, not the building's pipes. A vent that terminates where snow or ice can block it, or a condensate line that can freeze, are winter issues the installation has to account for.
Condensate in winter
A condensing tankless unit produces acidic condensate whenever it runs, and in winter a hard-working unit produces it continuously. The condensate trap holds a water seal that stops flue gas escaping through the drain; if the trap dries out, blocks, or the drain freezes, the unit can report a blockage code and shut down. Rinnai documents a full condensate trap as one of the named causes of code 10.
The drain path therefore has to stay open through freezing weather. Where it runs through an unheated space, that is a design consideration at installation and a check at the annual service.
Before winter
The practical winter checks are the ones already in the maintenance schedule: confirm the inlet filter is clean, the condensate trap and drain flow, and the vent termination is clear of snow and ice. Annual descaling also matters more on a hard-working unit, and it is a warranty condition on the RU199iN, whose lime damage is excluded from coverage.
CANRO Heating & Cooling services tankless units across its verified Metro Vancouver coverage and assesses demand, sizing and recirculation as separate services. A winter sizing question is answered from the flow-at-rise figures and the home's measured demand, not from the unit's maximum.