Fellow stove-top brewer here. To get my boil going, I have the kettle on the burner cranked up on high once I have started lautering. My mash tun sits above the kettle on a little step up stand with some books and a towel on top. Then I put some aluminum foil covering to cover about 80% of the kettle since I don't have a lid. Crank up the burner to max and hope it doesn't take too long. I'm planning on getting a handheld heating element for liquids to speed this up, which I saw on amazon.com.