An easy way to clean your oven, without resorting to those harsh, environmentally dangerous sprays is to use ammonia and water. Simply set your oven on warm for about 20 minutes, then turn it off. Place a small dish of full strength ammonia on the top shelf. Put a large pan of boiling water on bottom shelf and let it sit overnight. In the morning open the oven and let it air a while before washing the inside surfaces with soap and water. Even the hard, baked-on grease will wash off easily.