I have a house built in 1929. Much of the electrical has been upgraded to 200amp service, but there remains a fuse box that feeds some of the old outlets. The wiring in know & tube for these outlets.
There are some 15amp fuses and some 20amp fuses. I don't know if previous owners have installed the correct size fuses or not.

How do I determine the proper size of fuse to use? My wife plugged a space heater into a 15amp supported outlet and blew a fuse, so I think that one should be 15amp (!).