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As much of the United States struggles through the end of the nasty cold spell, a thought came to mind: Is it generally energy efficient to run the heat in my car?

Let me be a little more specific. I own a Chevrolet HHR, and as far as my understanding goes, heat is provided to the cabin by means of circulating part of the coolant loop near the blower when it is demanded (this much I think I know when I had to replace the heater core due to a mysterious coolant drainage).

Now, excluding the need for electricity being provided to the blower, am I essentially being energy efficient by using the engine's heat to stay warm instead of wearing my coat in the car, or is there a separate heating element that is using more energy?

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You are correct that the only extra energy consumed is the electricity used by the blower fan to move the warmed air. In the grand scheme of things the extra fuel required to generate that electricity is miniscule. The coolant is circulated regardless of the heater setting. Moving the selector to cool or warm merely directs all the air over the heater core or blends outside air.

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    I agree - it will make a difference but it will be so small that it will be lost in the noise of everyday driving. It's an entirely different situation than using the air conditioner.
    – Bob Cross ♦
    Jan 8, 2014 at 2:50
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    Yup. You've got to reject the engine's operating heat somewhere. With the heater on, some of the engines operating heat warms up the car's cabin. With the heater off, all that heat is rejected outside the car. The cabin air blower is not a large power draw, especially at lower speeds. Enjoy the heat. NOW, if you drive an electric car, the story is different. In that case, bundle up! The heat is an electric resistance element, so you're directly trading heat for range. Hybrids can provide heat like a conventional vehicle, or they might have some extra equipment including electric heaters, etc.
    – mac
    Jan 8, 2014 at 14:31
  • mikes: Thanks for clearing that up! @Bob I hope that the amount of energy I waste in the summer using my A/C, I can make up for by using the heat in the winter!
    – gcode
    Jan 8, 2014 at 18:40
  • @mac Interesting addition about the hybrids/electric cars there. I probably should have broadened my question to include cars that are not solely combustion engine driven.
    – gcode
    Jan 8, 2014 at 18:43
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Here's a nice tip: if you turn up the heat in your car, it helps lower the operating temperature of your engine. Sometimes by as much as 10%. Not a problem when you're driving around in icy cold weather, but if your car is overheating, turning on the heat, opening the windows and putting the blower on full could save your engine from popping a gasket.

If you turn up the heat and it lowers your engine temp to within optimal temperature range, I would argue that it actually improves economy. But that's just theory. But as others have said, the theoretical difference in fuel consumption is too small to measure.

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  • A very good thing to know. I was fortunate enough to know that beforehand, when my car's coolant tank was on empty on a summer day (this is related to the heater core replacement).
    – gcode
    Jan 8, 2014 at 18:44
  • Same here. My coolant pipe burst in our parking lot at work a month ago and I had to drive home 20 miles. It's summer where I live. It's a turbo, so it gets quite hot even when the cooling system works properly. It was quite nerve-wrecking.
    – Captain Kenpachi
    Jan 9, 2014 at 8:22

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