Heat pump defrost: what happens to fan coils and underfloor heating

During heating operation, the outdoor unit may freeze and the heat pump may require a defrost cycle.

What is defrost?

The pump temporarily reverses the refrigeration cycle to heat the external exchanger and melt the ice.

During defrost, the supply temperature to the terminals may temporarily drop.

The automation system may limit or stop the fan to prevent cold air from blowing into the room.

High thermal inertia usually makes the temperature drop less noticeable.