Heat the oven to 150 degrees Fahrenheit and turn it off. If you have a gas oven, turn off the gas and the pilot light. Place a pot of boiling water on the bottom rack. On the top rack, put a heat-safe bowl or baking dish containing 1 cup of ammonia. Shut the oven door and leave it 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 1-2 teaspoons of liquid dish soap to the ammonia, along with a quart of warm water, and using a heavy-duty 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.
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Pull out your owners manual or look up on line. I have a gas oven and just make a paste with vinegar and water.
Here is how to clean an oven with vinegar and baking soda: https://www.thekitchn.com/how-to-clean-an-oven-cleaning-lessons-from-the-kitchn-201191
Hi Caril; What I use is a paste of vinegar and cream of tartar (the dry stuff). Make a paste and put it on the gunk. Let it sit for about 15 or 20 seconds and then scrape off with a plastic putty knife or one of those plastic scrubbies. You may have to do it a couple of times if the gunk is thick, but usually not. A lot of people don't know, but on most stoves, the door comes off and the bottom of the oven also comes off. You don't have to take the door off to get the oven floor out. Sometimes it's hard to get the door back on:) There is no smell and it is environmentally safe. Good luck.