Yes, Power venter is ON all the time. I have been running my Keystoker 90K stove (in the winter) for 6 years now with a direct vent.
Once the power goes out, your fire will go out since the Stoker type stoves or boilers need a "combustion "blower to keep the fire going. The stove is pretty sealed, so the fumes will just migrate out the pipe even though the power vent is not on.
2 Terms for them.Power vents
typically mount on the outside wall and suck the fumes out of the stove, typically a 6" pipe.Direct Vents
are typically mounted to the stove and push the fumes out, advantage, smaller pipe (4") but pipes must be sealed.
If you do a search on here.....Direct vent vs Power vent...Direct vs power vents.Direct Vent Question