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What size tankless water heater?
Winter is the test: how many fixtures run at once, and can the unit still deliver at a ~40 °C rise? Choose the fixtures and see the published models that keep up.
Winter demand: about 9 L/min (2.4 GPM) at a ~40 °C rise
Compare that against each unit's published flow at a similar rise. This site publishes flow with its rise for every tankless model, because comparing brochure maximums quoted at different rises is meaningless. The catalogue figures closest to the winter condition are the 67 °F (37 °C) rise ratings below.Loading the published tankless models…
Want the winter number confirmed? CANRO measures the actual simultaneous flow and checks the gas supply and vent route before quoting a tankless installation.