Do I need a cooling fan in my ReplayTv 2000, 3000 or Showstopper?


As a rule of thumb you do not need a cooling fan if all four conditions are true.
1- When unit is stored in a cabinet and while the unit is in use, internal cabinet temperature remains close to room temperature. 
2- As a habit, unit power button is turned off when the unit isn't being watched. This allows the hard disk to spin down and cool off (scheduled recordings will still record even with the power button off).
3- Nothing is placed on top or sides of the recorder to obstruct air free flow through recorder.
4- Used in ambient temperatures below 95 deg F
You do need a cooling fan in any of the following situations.
1- You have enable disable disk spindown option (Keep Disk Spinning). This is a secret option that keeps the hard drive spinning at all times. The advantages are; unit's instantly on when the power button is pressed, i.e. you never see the "Please Wait.." screen after the initial boot up and the recorder continues to store in buffer any channel tuned whether the unit is on or off. Comes in handy when you want to back up to see portions of news or TV show currently tuned.  
2- Room temperature gets above 95 deg F.
3- An electronic box is stacked on top of the recorder.