Reply to "Heater core - keeping it cozy"

My car has the shut off valves, so normally there is no hot water to the heater core at all. Last January, I had to drive the car on a 28 degree day in light snow. I drove for about 40 minutes and the cabin was comfortably warm. I didn't have to defrost, though, so I might have needed the heater for that, but for simple driving, I see a functioning heater as a pretty low priority.