At any time, only some part of the world are loaded. Normally, that is within 128 blocks of a player in the x and z direction - height does not matter.
So if you go more than 128 blocks away from a furnace, then it is no longer loaded into memory, and is frozen in time until you get close again.
The only exception (in vanilla Minecraft) is the "spawn chunks", which are always loaded. It's where the player originally spawned in the world (not their spawn point that they can set by sleeping in in a bed). A compass will point to the world spawn point.
(There's some more complications, such as on multiplayer servers running certain software or configurations)