Yes, a torn hot tub cover will waste energy because the water will be heated, yet the heat will be continuously escaping through the tear in the hot tub cover. This method therefore requires more energy use to maintain the heat. In order to stop wasting energy, the hot tub cover will have to be replaced. However, if you want to save energy, temporarily repairing the tear with duct tape will reduce the heat loss and consequently less energy will be wasted. In short, using a torn hot tub cover is not a great idea.