My brother had an old farmhouse and found out the hard way that there was a run of lower rated wire inside one of the walls. He had a space heater plugged in against the outside wall but someone had added an outlet to an inside wall on the same circuit and used cheaper wire just in that section, so a fire started inside the wall. Luckily he noticed the smoke coming from the outlet as he was heading to bed for the night. If he hadn't noticed it he may not have woken up. He had so many similar crappy DIY problems with that house he probably replaced 60% of the house before he sold it