Tracking runtime of a furnace/AC unit

I used to have a ZWave Trane thermostat that tracked the runtime of the furnace/AC unit. I switched to a non-ZWave WiFi thermostat that doesn’t track the runtime. Is anyone tracking their furnace/AC unit runtime without a ZWave thermostat, and if so, how are you doing it? Thanks.

You can do it with PLEG and an Input counter.

I bought PLEG and have used it for some very simple logic problems. I just scanned through the PLEG Basics manual but didn’t see anything that might steer me in the right direction. Unfortunately, mios.com is down right now so I can’t even try to figure it out by playing with PLEG. Would you have any boilerplate example for tackling something like this? Thank you.

UPDATE: Just wondering. Since the thermostat is not ZWave, can I even use PLEG? How would PLEG know that the thermostat is going on and off?