I've been working on dehydrated heat. Add your own boiling water and this stuff gets hot enough to burn your skin. You can even heat houses with it. Best thing is the low cost. I am now selling 1# concentrate bags for $100. If you add 10,000 gallons of your own boiling water to this, your cost for the dehydrated heat is only a penny a gallon. (The cost of the boiling water varies by region.)
But you know some people will try to stretch a bag to last 20,000 gallons in order to save money.