The answer depends on the hardware version of your NVR.

Applies to: Reolink PoE NVRs.

RLN8-410 and RLN16-410 NVRs with an old UI come with a fan inside. RLN36 NVR with new material also comes with a fan inside. And you can replace the fan of your NVRs.

RLN8-410 with a new UI is built in with a heat sink, so there is no fan inside. The newly released RLN16-410 has both a fan and a heat sink inside, and you can take out the fan to only use the heat sink.