No heat in car makes for miniscule savings

Dear Tom and Ray: My neighbors have decided that they shouldn't use the heaters in their cars this winter so that they can save gas. (Really, I'm not making this up!) Since the heater is basically using waste heat that the engine is producing anyway, it doesn't seem to me that there could be any gas savings, other than the minimal amount of power needed to run the fan. Are they really eccentric, or am I missing something? (Actually, I already know that they're eccentric, but they could at least be warm and eccentric!) This reminds me of the stories about people in Russia who drive with their lights off to save their batteries.

Alan

Tom: Yeah, they're nuts, Alan. But technically, they do have a point. Under normal conditions, the heat is essentially "waste heat" and would be lost to the atmosphere anyway.

Ray: Once the engine is warmed up, coolant circulates through it to absorb excess heat. Then the coolant goes to the radiator, where the heat is released into the air.

Tom: When you turn on the heat in the passenger compartment, you open up another "radiator" inside the cabin. When the hot coolant passes through that radiator (known as the heater core), heat is also released onto your tootsies. So, generally speaking, when you use the heater you're not "stealing" anything that is needed elsewhere.

Ray: But if you want to be picky about it -- and clearly, your eccentric neighbors want to be picky -- there are situations where you would give up a little bit of gas mileage for your heat. One is if you use the heater during the first few minutes of driving, when the engine is still warming up. Until the engine reaches operating temperature, it's not operating at its peak efficiency. That means it's using more gasoline.

Tom: So, if you're calling for heat that could otherwise be recycled into the engine during those few minutes, that's a few minutes of sub-par mileage. But the difference is miniscule.

Ray: The effect is somewhat greater when you're driving in bitterly cold weather. When it's well below freezing, the engine may be working hard just to maintain an ideal operating temperature. And again, if you're drawing off heat and the engine is running below its ideal temperature, your mileage will suffer a bit.

Tom: But which would you rather give up? A few tenths of a mile per gallon, or your core body temperature?

Ray: Duh! Most people accept slightly lower mileage in the winter in exchange for not turning blue. That's what we recommend.

Tom: But to each his own, Alan. If that's a trade-off your eccentric neighbors are willing to make, good for them. Just be sure you offer to drive if you guys go anywhere together before the spring thaw.