Add Fresh Manure
The key ingredient to making the hot frame work is fresh manure. As it decomposes, it gives off heat. A good manure to use is from cows or horses and can be obtained for free or at nominal cost from a local farm or stable. You can also use poultry manures or bat guano, which can be more expensive and hard to find. Avoid using dog, cat or human manure, particularly when growing vegetables, as they can transmit disease. Wear old clothes and fill the pit with a six-inch layer of manure. Break up any clumps with a hard rake and tamp it down lightly with a shovel. Moisten the manure with water to help build up heat inside the frame.