Identify the actual defrost energy path

Request the selected heat pump's mode description and hydraulic configuration. Determine whether defrost uses water-circuit energy, a storage tank, another heat source or a different documented arrangement. Caleffi describes reverse-cycle defrost and heat withdrawal from water-side thermal mass. Those examples do not establish the same behavior for every heat pump, and their control settings are not instructions for an unrelated installation.

Record heat flow with an explicit sign

Define positive thermal delivery toward the served load and distinguish that from positive electrical consumption. During the reviewed defrost state, the thermal quantity can decrease or reverse at a particular boundary even though electrical input continues. If backup heat maintains room service, keep its input and heat delivery on separate lines. Do not count both withdrawal from storage and continued normal heat output without a balanced energy description.

Name the thermal meter's location when interpreting a defrost event. A tank outlet, heat-pump connection and room circuit can show different simultaneous flows because they enclose different parts of the system.

Assess service and recovery together

Ask the heating designer how the approved circuit maintains required flow and temperature during defrost, and how any used thermal reserve is restored. Compare wind with the actual electrical sequence, but evaluate heating service using thermal evidence. This is a heat-direction question, not a claim that all defrost energy is an additional electrical load. Include the signed thermal boundary, configuration and accepted recovery case in the RFQ. No defrost capability, heating guarantee or heat-pump control feature is established for MARSTON equipment.