A natural source of heat is flame, and there are several tools that can create flame to provide quick heat. However, you shouldn't use anything that creates a flame, such as a torch or a heat gun, to unthaw your pipes. \
Too much heat can do damage to pipes, the same way that too much cold can damage pipes. You may want to find the quickest method to unthaw frozen pipes but quicker is not better. \
Use less harsh methods to heat up pipes and they will unthaw, not immediately but safely. \