What the system does
A gas tankless heater heats water as it passes through the appliance. The flow it can deliver depends on the heat it must add. A maximum-flow label without incoming-water and outlet conditions is incomplete sizing information.
Bring the right information
Record the project address, present model and fuel, hot-water use, the location of affected fixtures and accessible photographs. Explain whether the goal is replacement, greater capacity, reduced waiting time, a fuel change or a wider renovation. Those goals can lead to different designs.
What the proposal should resolve
Ask for the actual performance curve, simultaneous-use assumptions, fuel-supply assessment, vent route, service access and model-specific maintenance plan. A compact appliance can still require substantial installation work.
Compare the complete commitment
Keep the equipment model and performance evidence with the installed price. Include associated trade work, removal, permits where required, commissioning and warranty responsibilities. Treat future operating costs as a separate calculation with explicit consumption, rates and currency.
A product category is a useful starting point. Final suitability and availability require the actual model, property assessment and a written proposal.