The real answer to this question is about 10% of the stored energy of one level becomes stored energy at the next level higher.
Think about it, when a consumer eats the producer it also consumes the energy the producer stored and as the food chain grows the energy is passed through all. The only time the energy is released into heat is when a consumer dies and decomposes, and even then all of the energy isn't released.
The choice that is true of the energy that is passed from one trophic level to the next in a food chain is about 10% of the energy passed from one level to the next is released as heat.
