The dealer threw one in for no charge when I bought my JD 4120 about 5 years ago so they cant be too expensive. As far as keeping it plugged in, like others stated, that is a big waste of electricity but more importantly, it will result in premature failure of the heater (they are good for only so many hours so it dont make sence to use them up sooner than necessary). I know this because we have a Cat diesel gen-set at work that the block-heater is left on continuously all winter and we rarely get more than a couple winters out of a heater. For my tractor, 45 minutes is enough, 30 will do in a pinch, but I usually go for an hour or so. The block heater is probably the smartest thing you can add to a diesel used in cold climates, because it reduces engine wear, and lets you work the machine hard immediately after cranking it over. Also, depending on your situation, you may not need to waste any cash on timers, remote switches, etc.. I take a 4wd truck to work each morning, which will make it thru up to 24" or so of snow, so I dont bother plowing until I get home from work (that also lets me sleep in a little longer each morning). When I get home from work and pull the truck in the barn, I plug in the tractor. Next, I go in the house and eat a nice relaxing dinner with the family. After dinner, I go out and plow the driveways, the tractor now perfectly "warmed up". I do keep a gas tractor with a plow on it as a backup. That also gives me an option, with no need of a block heater, for getting rid of more than 24" of snow in the morning.
