That's exactly right: typical fireplaces sucks the air out of the room, or house, to feed the fire.
But, I am not sure if I'd say all fireplaces are bad. There are direct-vent fireplaces that pipe outside air, aka "combustible air", into the fireplace to feed the fire so it doesn't use the room's air. It is code in some places because it helps to percent back drafts into the house with negative pressure, like a kitchen hood fan activated.
https://www.google.com/search?q=fire...ion+air+intake
^- an example I was thinking of.
They work on the same principal as direct-vent wood-stove heaters (hearths). The difference I believe is that a wood stove would radiate almost all their heat in the surrounding air, whereas a fireplace radiates heat out in front, but also into the walls.
I'd be willing to place a small bet that with enough river rock, slate, and large logs, the amount of thermal mass in a log home could soak up that heat into the logs and river rock where it would be released long after the fire dies out.
I've been on the fence about thus myself since my green building research where they go over the pros and cons of wood stoves and fireplaces like this. In short, a direct-vent wood stove is almost always more efficient, because you are radiating all heat into the room.
Then, I found out about circulating fireplaces. Think of a wood stove in a wall, with a fan that draws in cool air from the bottom and forces out warm, radiate-heated out the top of the fireplace like a forced-air system does. Something like this:
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