I don’t drive much (5000 miles per year). How often should I flush? What is appropriate range? Owners manual does not say much.
I wouldn’t do a coolant flush if you’re not having problems.
What car do you have?
I recommend replacing the coolant (drain and refill the radiator and the block) at the scheduled time intervals listed in your maintenance schedule.
At the miles you drive, every 5 years or so, drain and refill; no need to flush unless the system is full of crud to start with.