Modern designs use direct vent systems, where instead of using inside air for combustion, they bring in outside air (and then exhaust externally as usual):
* https://www.efireplacestore.com/five-things-about-direct-ven...
The warming of the house occurs via radiant heat and through any conduction of heat via the actual material of fireplace or stove.
Also they built homes much smaller (the average home was less than 1000 sq feet 100 years ago, today it's 2400) and they tended to have smaller, compartmentalized rooms. This allowed for the inefficient home to use less energy anyways.
Where I live there are quite a few ~120 year old homes that are about 2400 sq feet. These would have been built by fairly wealthy people of that time as evidenced by old directories which indicate a live-in servant at most addresses, rift sawn moldings and floors, and stained glass windows on landings/in dining rooms. And although inefficient, they are smaller so they use similar amounts of energy to much larger modern homes.
Was it purposefully desgined to do this, or did it just happen because of construction methods of the time?