Not everybody needs block heater but in Alberta dealers install them in every Prius (and charge us). I was just experimenting with the block heater and I think it is worth it. Outside temp -12C (10F) Inside garage: 0C (32F) I have hooked up UltraGauge to ODBII port and was reading coolant temp. Coolant temp. same as inside garage 0C (32F) Prius V plugged in for: 30min. (coolant temp.) 23C (73.4F) 1hr. 10min. (coolant temp.) 30C (86F) After starting Prius the coolant temp. dropped down by 3C (5.4F) as coolant start circulating. So plugging the Prius only 30min will definitely help to start the engine better and in break-in period. The RPM of Prius is relatively low but I'll post the result in few days (still collecting data).