Charred cheese from a pizza or the overflow from a pumpkin pie may remind you every time you use your oven that they're still there, becoming baked-on grime. Cleaning an oven is a nasty job that many people put off. Using ammonia as an oven cleaner is one option that may prove to be a simple fix for handling tough built-up grease and fat in a dirty oven.
Choose a fine day so you can open all the windows in your home to provide proper ventilation during and after the cleaning. Ammonia is a caustic cleaning agent, and its fumes can be overwhelming in a closed-up room. Preheat the oven to 150 degrees F. While the oven is heating, put on a pot of water to boil. Once the oven has reached 150 F, turn it off. Pour a half-cup to a cup of ammonia in a heat-safe bowl and place it on the top rack in the oven. Place the pot of boiling water on the bottom rack. Close the oven door, allowing both the bowl of ammonia and the pot of water to remain in the oven overnight.
The next morning, open the oven and remove both the bowl of ammonia and the pot of water. Don't dispose of the ammonia; you'll want to use it later. Remove the racks and leave the oven door open to air out for 15 minutes. Add a few drops of liquid dish detergent to the ammonia, along with a quart of warm water. Wear some kitchen gloves, since ammonia can be caustic to skin. Spread some newspapers on the floor. Using a nylon scrubbing pad dipped in the ammonia mixture, begin to wipe away the softened grease and grime along the sides and bottom of the oven. It should be a fairly easy job at this point. For stubborn patches of grime that haven't softened completely, try applying full-strength ammonia to them and waiting about 30 minutes, then wiping away with the rinsed nylon scrubber. Rinse the oven walls frequently to reduce the odor of ammonia. An oven door gasket should not be cleaned with an ammonia or other detergent solution; wipe the gasket with a soft, dry cloth to avoid leaving a chemical residue behind that could degrade the gasket material.
Wash lightly-soiled oven racks in the sink with warm water and the ammonia/detergent solution. Sometimes oven racks can be particularly hard to clean. If they're still stubbornly soiled even after the overnight-ammonia treatment, try putting them inside a large, dark garbage bag. Pour a half-cup of ammonia over the racks inside the bag, tie the neck of the bag and place the bag outside for a few hours. Bring the racks inside, wash in the sink and wipe clean.
Don't use ammonia to clean a gas oven. Never mix ammonia with other strong cleaning agents, such as bleach or commercial oven cleaners.