1. I agree – most cars do use engine coolant, however it is possible to run the heater fan without starting the engine, although of course, it doesn’t mean the heater will blow hot air. For example, if you turn the vehicle on, but don’t turn the engine over, the heater can be turned on but you’re not going to get any warm air from the heater, no matter how long you keep the heater on. The engine would have to be turned completely over for the heater to generate warm air.

2. Carbon Monoxide: If you had the engine running, turned it off but left the heater fan on OR had the heater fan on for some time while the engine was running, turned the engine and heater off and later turned the heater fan back on without starting the engine, you run the risk of carbon monoxide poisoning, should you be uaware that you have a leak in your exhaust system or you are unaware that the tail pipe is covered or blocked with snow, which doesn’t allow for proper air flow.

Naturally, you also run the risk of carbon monoxide poisoning if you have a leak in your exhaust system and your heater fan is on while your engine is running, as well.

I had a friend pass away due to carbon monoxide poisoning in her vehicle. She went to her car on her work break one winter evening, started the vehicle up and kept it running for some time just to make certain it would start later, turned the engine off and because she had time left on her break, decided to stay in her car and read a book, but left the heater running – which was still blowing warm air. Unforunately, she died later that evening due to carbon monoxide poisoning from a leak in the exhaust, which found its way in through the vents.