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I have asked a few people whose cars are idling if they mind switching them off to reduce pollution. One response I get from quite a lot of people is that they need to keep the car running to enable the heating to work, otherwise they will get cold.

Considering taxi drivers, those sitting in their car during lunch hours, those waiting and all other people; what ways can you keep warm inside a car without idling and without using the internal heater?

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  • Please edit your question to give a maximum time and minimum outside temperature (define 'cold'). Half an hour or two hours makes quite a difference. So does 0C or -10 C
    – user2451
    Nov 15, 2019 at 19:32

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It's possible to fit a dedicated heater run off the fuel system. This is a much more efficient way of turning fuel into cabin heat. They're common in motorhomes in a form that directly heats the cabin air by burning diesel, but in smaller vehicles they work with the existing fans and heater block. Either way they have their own exhaust system.

Yes, they burn fossil fuels, but they do this in an optimised way, which uses a lot less fuel compared to running an engine to produce heat.

(I've linked to a leading brand, as their website is more informative than anything else I could find)

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  • For petrol engines it is a much more efficient way. For diesel engines it is a "hmmmaybe".
    – Stian
    Nov 15, 2019 at 21:37
  • @Stian, why's that? Diesel heaters for motorhomes and some work vehicles were where this started, because they use so much less fuel than heating via the engine
    – Chris H
    Nov 16, 2019 at 7:22
  • Because of the compression ratio and the rotating flywheel mass diesel engines use very little fuel when idling, and it is common enough to just let the engine run over night when it gets cold enough. But yeah, a heater is a good answer - for petrol engines it is clearly the better choice, and for some diesel engines it is.
    – Stian
    Nov 16, 2019 at 12:16
  • @Stian figures from 2015 say otherwise for cars, and even if there's been a revolution in fuel economy since then, most cars on the road are older than that. For that much fuel you'd get 4kW from a diesel heater which is several times what you'd need to warm a car cabin.
    – Chris H
    Nov 16, 2019 at 14:30
  • ... Delivery trucks use so much more at idle than cars that keeping a cab warm would use 30x as much fuel using the engine at idle compared to a dedicated heater. (900W should be enough). Figures from links in my previous comment. I'll probably expand this worked example into my answer, when I'm at a pc
    – Chris H
    Nov 16, 2019 at 14:33
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  1. Wear a woolen underlayer (woolen socks + woolen long sleeve t-shirt + woolen long pants)
  2. Wear warm clothes (hat, snood, scarf, warm jumpers, warm trousers)
  3. Wear winter driving gloves (or any warm gloves)
  4. Drink hot drinks
  5. Keep a flask of hot water in the car
  6. Buy an in-car kettle (charged from cigarette lighter)
  7. Heated car seat cover
  8. Warm blankets (wool is usually best)
  9. Heated car blanket (charged from cigarette lighter)
  10. Keep the heater on
  11. Fit a dedicated heater to run off the fuel system
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    I wonder about the efficiency of using the cigarette lighter. Its power comes from the car's battery which is recharged when driving, so basically you are still using fossil fuels to get warm. Doesn't that defeat your purpose?
    – THelper
    Nov 15, 2019 at 11:53
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    @THelper battery charging efficiency will be much greater when driving than when idling.
    – LShaver ♦
    Nov 15, 2019 at 12:52
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    @THelper also you're heating the person who needs to be heated, rather than heating the entire engine, cooling system etc. just to collect some small amount of that heat and use it to warm a poorly insulated cabin with lots of windows. You can draw up to about 150W from the lighter socket (don't do that for too long or you'll flatten the battery) while even idling an engine burns a few kW of fuel.
    – Chris H
    Nov 15, 2019 at 16:49
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    The engine block will stay warm for some time after turning off the engine. If you leave the fans running on low it should help keep you warm. I haven't tried this myself but I imagine it would be sufficient for 30 minutes or so, depending on how cold it is outside.
    – LShaver ♦
    Nov 15, 2019 at 17:08
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    @LShaver Running the heater with the engine off will provide warm air for a couple of minutes at most. The engine block will retain heat for quite some time, but that heat isn't available unless coolant is being circulated.
    – Carey Gregory
    Nov 15, 2019 at 20:46

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