To a child, my Grandmother's basement was an enchanted place, filled with marvels.
One that I remember very well was the furnace. It started life as a coal furnace. It was big and had no fan. A gravity furnace, utterly silent in operation.
It was so large that you could crawl into the combustion chamber through the coal door that was easily big enough for a child. But we never did this, we had too much respect for this monster.
It had two giant cold air return pipes, each one itself larger than a modern furnace. The connected to giant air boxes at the bottom. From the top of the furnace came a tangle of smaller pipes, small only in comparison, still much larger than modern ductwork.
Some time in the thirties, it was converted to a gas furnace, one of the first in the neighborhood. A huge burner ring, perhaps three or more feet in diameter was installed where the grate for coal used to be. It was awesome, and a bit scary, to have the door open when it lit.
The first thing the new owners did when my parents sold the house in the '80s was to rip out this beautiful old piece of equipment and replace it with a modern forced air furnace.