Hi, I have a rig for my contraption all drawn up and what not, Guess you could call this a red neck heater if you wanted to. My theory is to super heat rocks in a wood stove and use them in a long metal tube along with a squirrel cage style fan in the back of my car for heating.
What I need to know is, what rock would best do the job. I need a rock that would retain heat for a long period and purduce a lot of heat while doing it... Any suggestions?

Your biggest problem when choosing a rock type is stability. Some rocks can crack, and even explode with some force, when heated. Granite is fairly stable. Insulation will also be a problem, you do not want the metal tub to touch anything and cause a fire. What happens if your in a head on collision? Hot rocks flying every where that's what.

Yeah we thought about that and thankfully decided not to emplore the use of that heater for very long. I tried it once or twice but rocks just do not hold heat well in michigan's winters. Thank you though, exploding rocks would have been good to know about had I actually put this system into practicle use.

Ever had a rock in a bonfire? Same thing - no warning and rocks everywhere. What does the landlord say about your homemade heating system?

My landlord is my father and he helped me build it lol. We were using his wood stove to heat the rocks so if they were to explode it probably would have been in there but the stove wasn't getting hot enough I think. It only reaches a max temp of about 170 degrees F. While it was warm enough to get them hot, it was not warm enough to get them red hot. It was a very dangerous contraption and we ended up scrapping the idea early in its use