Starting the car with the heater on

I remember being told that you should turn off the air conditioning in the car when you shut the engine, since the AC can be ruined if it’s on when you start the engine.

Is the same valid for the heater? This past week, I’ve been leaving the heater on as I kill the engine, so I don’t have to remember to re-start it when I start the car back up again.

Is this a good idea or not?

(I have a 1997 VW Golf, automatic transmission.)

It does not matter. The only energy drain is the heater blower(fan), which is relatively weak. Besides, I believe, a “killer” circuit is installed in all modern cars, i.e. all electrical circuits are automatically shut off when the key is turned to “Start” position, including air conditioner. You can check it by leaving your radio on. It is suppossed to go silent during start.

Also, you won’t damage the heater by starting the car with it on, which seems to be at least part of your question.

The heater is a relatively simple device – it’s just a small radiator filled with water from the engine and a fan to blow air across it. If your engine is cold the engine thermostat closes and no water runs through your heater. When the engine warms up the thermostat opens and allows water to pass through the heater, the fan blows air across the heater’s radiator, heating it up, and into the passenger compartment (through some ductwork).

Even when your heater is “off” hot water is passing through it – but the heated air isn’t ducted into the car. So, as peace said, unless you’re worried about the small electrical drain from the fan you don’t need to turn the heater off when you turn the car off.

That is, unless it’s a newer car that has an electric (or electric assisted) heater so that it’s hot instantly (Camrys come to mind). But then, THAT won’t be damaged, either.


I believe that is true with most cars. But some cars have a “heater control valve” that cuts off coolant flow to the heater core.

Homer, you are right. I doubt that the electrical heater (steering wheel’s or butt warmer) will work off the batery, but, in any case, all circuits are shut off during “Start”, including air conditioner and heater. Modern cars are made pretty much “idiot proof”. I.e. if you fotgot to turn the air conditioner off before you shut off the engine yesterday, today you won’t be able turn the AC off, before the engine is running, anyway. So, you HAVE TO start the car with the AC on. The AC will not function during the “Start”.