Bjorn:
Hello! I have both kinds of heater shown in the pics from Ebay. The little control box shown with the yellow light on it is what we use. You need one for each heater. The water heater is for heating the engine for cold weather starting. I put one on my 5 ton wrecker, and it works great. The larger heater I use in my expandable shop van trailer. It will keep it very warm, run you out in fact on high. There is no thermostatic control for either heater I know of. The control box has high and low settings on the toggle switch. For the engine heater, the fan speed and output is varied by the high/low. On the large heater, the fuel input is varied by the high/low, the fan speed stays the same. I bought a 24 volt converter to run the one in the shop van. We use the shop van for our clean room for final engine and transmission builds.
I think these came out of armored vehicles of some sort, maybe Bradleys. There is a through the hull fitting for the exhaust. The large pad is for crew heating. My engine heater also had a circulating pump and a pad that goes under the batteries to heat them with water flow while the motor is heating.
I timed it one winter day, and in 15 minutes the engine heater had the snow melting off the hood.
Parts and manuals are still available for both from Soouthwind. They are very sensitive to clean fuel. If some particles get into the fuel block, the small holes there get obstructed and mess it up. You have to carefully clean the fuel block. My son and I have rather extensive experience with both types if you need help, we can try. Sam Winer Motors said they take the engine heaters off trucks and throw them away! I told them to put them in a barrel and call me!
Regards Marti