The Cold-Day Delivery Ratio

Every manufacturer publishes a limit temperature. Almost none publishes the output at that temperature. This works the other way round: pick the measured point closest to your design day and see what actually reaches the loop.

Each ratio belongs to the model and leaving-water temperature shown, not to the whole range. Ask for the correction table for your own design point rather than reading across. Adding margin on top of a derated figure is not free — the Consortium for Energy Efficiency reports that oversizing affects heat pump efficiency more than other HVAC types.