I have two gas fireplaces, neither use power (nor have any available). Valves and safety is handled via millivolt thermopiles in the pilot light and main flame

I have two gas fireplaces, neither use power (nor have any available). Valves and safety is handled via millivolt thermopiles in the pilot light and main flame. Heating happens via convection through ducts that run from below to around/behind the fireplace itself, then out over the top. It passively moves a fair amount of air and can make the room uncomfortably warm if left on too long. I have no idea if this is common or not, but I know of at least two counterexamples to your statement here in Michigan.