The amount of energy releases is the determining factor if you feel heat. For example, moss decomposing a rock has an exothermic reaction occurring, just not very fast and not releasing a lot of energy all at once. Fire burning a piece of would is an extremely fast reaction that releases a lot of energy all at once. That energy is what you feel as heat. The problem with hydrogen peroxide is that it more than likely doesn’t release a lot of energy very quickly. Therefore it may not seem hot to you. It is a common misconception that it is a good antiseptic. Most people believe that the foaming is a big reaction cleaning out a cut. It is actually the hydrogen peroxide reacting with the catalase in your blood cells and just breaking down into oxygen and bubbling up through the liquid.