PIDs, furnace valves, and duty cycles.

[rickyspeak]

I've dug a bit through the forums and I haven't seen anybody address this question. What is the ideal range duty cycle for using PIDs to run typical gas furnace valves like the Honeywell VR8200? How long is too long causing oscillating temperatures and what is too fast causing damage to you're gas valve from running too many cycles?

I'm guessing the upper end of most PIDs at 100sec it probably about right. I just thought it would be good to summon the power of the HBT before buying a PID. Thanks for your help.