Dehumidifier - Exhaust Air Temperature Warm

Warm or hot air coming from under or behind the dehumidifier is normal and part of the dehumidification process as long as the unit is drawing moisture from the air.
When the unit is dehumidifying, the compressor is generating heat as it operates. In order to avoid having the compressor overheat, air is drawn by the compressor at a rapid rate and exhausted from the unit. The warm air will stop shortly after the unit has reached the desired humidity.
Note: When running in defrost or fan mode, the compressor shuts off, the fan will continue to run and the room air will accelerate the defrosting process. When the unit is in defrost mode, it will actually blow cold air into the room. There is a thermostat that triggers the defrost. which goes off based on time and temperature.