the good things for a stone keep castles are: hard to set fire on the stone strong high (motte+bailey castle has weak wood so a srong bull could knock it down!) the keep was taller than the walls so the defenders could see enemies!) thats all.
GOOD-They were good because the were highly protective and strong.BAD-People could dig under the castle,make a fire-Therefore the stones would heat up and crack, making it easier for the enemy to...
Heating techniques probably varied by region and epoch. The Short answer is: 1. Heated 'masses'. and 2. building fire was a science to people. A common house design going back a couple hundred years...