I've gone back and forth on this several times, but at the moment I keep the HR20 in standby when not used. It runs cooler when left in standby.After 10 minutes it stops buffering live TV and that's probably the reason for the heat dissipation.
Heat is important to me because my HR20 is in a closed cabinet with only one 3" diameter hole for airflow. With a USB-powered fan placed right over the processor's heat sink, I run 115 when left in standby, and 119 when left on. I know the unit is ok operating up to 128 but I'm trying to find a good place for the fan where it will still do enough cooling when it's 80 in the house in the summer.