ndiy, you neatly outlined the reason why I have not tried it on the fridge, the fridge looks as though it may be about to die without my help anyway.
The heater is just men't to keep a cup of coffee warm but I use a tea pot with about a litre of water.
The little gen set cost very little, I'v got 3 or 4 alternators, the motor came from a garage sale $NZ10, the wheels on the sack barrow $NZ13 each, every thing else out of the junk box. Automotive alternators are inefficient, and a better genny could be built with little difficulty, with that I would expect to get about 1.5k Watt with the 3 hp motor.
Ian S C