A freeze plug type block heater left plugged in all the time will add up to about $10-15/month extra on your electric bill, a large tank type will add up to $20-25 if left plugged in all the time. I use 1000 or 1500 watt tank type heaters, and 675 watt freeze plug heaters in these engines. They heat the engine the same if installed properly. Tank type heaters are by far easier to install than freeze plug heaters if the engine is in the vehicle, which is the only reason I use em at all. The 1100 watt freeze plug heater in my dad's bucket truck heats the Navistar 7.3L N/A commercial diesel to 60*F in about 24 hours @ 10*F outside temp, and when plugged in on average 150 hours a week, adds about $20/month to the electric bill. Thats a small price to pay to be able to answer emergency "half a tree fell on my house" calls after an ice storm.