Heat pump sizing margin

Heat pump sizing margin is the deliberate allowance between the calculated design heat load and the selected heat pump's usable heating output, read with emitter output, flow temperature and manufacturer performance data. In MCS heat pump design, the heat pump still has to cover at least 100% of the calculated heat load without supplementary electric heating at the design point. A margin can help with heat-up after setback or intermittent heating, but excessive margin can contribute to cycling where the home needs less heat than the unit can modulate down to. It is not a fixed percentage, a comfort guarantee, proof of correct sizing, permission to rely on backup heat or evidence that the nearest model size is acceptable.