Leaderboard

I would suggest you go with a heater that uses a heatercore for the heat, the only electrical draw-is from the fan. plenty of heat and You cant see any effect when the fan is running such as dim lights etc. Kits are fairly pricey ($399) for the Ice Crusher I bought, but if you are really handy, you could do an install from generic units on ebay and the like.

I've never seen a spec published anywhere, maybe someone will chime in. I doubt theres enough overhead to run an electric heater that puts out enough to be worthwhile. My experience with these types of things is there might be 10-15 extra amps of overhead MAX at idle, quite possibly less. A 100 watt light bar will eat half of that. A 100 watt electric heater would eat the other half and isn't going to heat the cab. If you feel like experimenting you could keep adding load until the battery voltage is <14V at idle, that will give a good idea of the max limit. Dont forget to turn on the factory lights (35W ea), brake lights (10W ea), turn signals (10W ea), etc as all that has signifigant draw.