how my $20 space heater has hot air after 5 seconds while my car takes 3/4 minutes



Edit: meant to put 3-4 minutes not 3/4

In: Engineering

Your car’s heater is getting free heat from the engine, but that only works once the engine gets hot, which takes a few minutes. The space heater is taking energy from the power mains, which is faster to heat up, but you have to pay for it.

The heater in your car relies on the engine for heat. If you start the engine and let it run for a few minutes before turning on the heat, you’ll find it’s warm very quickly.

The car heater works on the heat of the engine – it “has to” heat the entire radiator to a decent temperature first (if you try to suck the air from it too quickly, you will literally cool the engine even more which you don’t want on a cold-start). The engine runs, heats the water, the water heats the air in your car.

You can *get* electric heaters, etc. for the car, they are usually stupidly pathetic (12V, often limited to only 10A on a cigarette lighter socket, is 120W) or aren’t something you can have running for more than a few minutes, when the engine has just started, or in cold conditions.

Basically, you sacrifice your heat for the first minute or two of operation to keep the engine running smoothly in cold conditions, then when it has an excess of heat it’s designed to give you that.

And anything that sucked the power from the engine in those first few minutes will hinder a cold-start and will, also, take a huge drain and leave you with a flat battery if you use it for more than a couple of minutes.

I used to have a Ford Mondeo (Fusion in the US, I believe). It used to have a coil-heater in the airvents. It could blow hot air immediately, but it was a draw on the battery, and even then it wouldn’t kick in immediately.

It was also notorious for failing and even starting fires.

I have a newer Ford Mondeo. It does not have that.

Manufacturers will tell you – the best way to warm up the car in cold conditions is to drive it normally, and not too much strain on it. Suffer that minute-or-two when you’ve just got in from the cold outside, and are now in a cold, but not windy, car. Because anything else will leave you with a flat battery, an engine that can’t crank, or a fire hazard.

As others have said, the heater in your car pulls free heat away from the engine. It works like this:

When you first start your car, the engine is cold. Inside your engine are pathways where engine coolant (water mixed with chemicals that are resistant to freezing) flow to keep your engine from getting too hot (overheating). The way it keeps your engine’s temperature down is by cycling the engine coolant from your engine through the radiator and blowing air (by using a fan as well as forced air as you travel down the road) over the fins of the radiator.

Actually, there is a device in your engine that delays this cycling of coolant in order to speed up the engine warming to normal operating temperature (about 165 – 180 F). This device is called a thermostat and it remains closed and blocks the flow of coolant into the engine until it reaches a certain temperature (or it would take even longer for the heat in your car to start working).

To heat the air in your car, it has something called a heater core which is mounted somewhere under/behind your car’s dash. This heater core is basically a smaller radiator. A fan in your car’s ventilation system blows air over this heater core and into the passenger cabin. Until hot coolant flows into this heater core, you will not have any warm air coming from your car’s vents.

As a side note, it’s easy to tell if your car’s thermostat has broken in the open position. Your engine will take a very long time to reach normal operating temperature and your vehicle’s heater will similarly take a very long time to start producing warm air.

Additional side note, the heater core on my 1968 Plymouth Valiant popped one morning on the way to work and instantly dumped hot coolant into the passenger floorboard of my car while simultaneously seriously fogging every window in my car. I had to stick my head out the window to make it safely to the side of the road.

Car heater uses waste heat from the engine coolant. The engine is large and there’s a large volume of coolant in the water jackets of the engine.

The engine has to heat it’s self, which heats the coolant, which is moved by the water pump to the heater core, a small radiator in the climate control duct.

Once the engine is at operating temperature the thermostat (physical variable valve, opens up with increasing temp) will open and begin moving the hot coolant to the radiator where the coolant is cooled by airflow, the cooled coolant then flows back into the engine and the circuit continues.

This question makes me wonder if I’m supposed have the AC on when I have the knob turned to hot.

Does the AC power the heater too or should I just leave it off as heat only comes from motor?

I assume it needs to be off because I haven’t been able to find a difference.

Car heaters work by redirecting some of the engine coolant/antifreeze liquid away from the front radiator.

This doesn’t work however until the engine block itself warms up, which usually takes several minutes depending on the ambient temperature outside. Until that time, the circulating coolant will be no warmer than the engine block is.

Ypu can remedy this in two ways, the first is to throw away and organize the stuff in your garage and actually park your car in there if you own one. The second way is to buy an electric block heater for your car which plugs into one of your exterior outlets. This keeps the engine block generally above 0°C and reduces the amount of time needed to warm up in the morning.

Ocassionally some car makers have used electric heating elements to provide rapid heating. But this would actually consume a lot of electricity, which might drain the battery and would require a larger alternator to run which would soak power from the engine in a noticable way. Many modern cars have heated seats available as a purchase option. Unlike attempting to to heat all the air flowing continuously through the AC system, running a seat heater doesn’t consume that much electricity so this generally doesn’t necessitate major changes to the car electrical system.

In some of the newest cars the AC is designed so it can run in a *Heat Pump* mode. Essentially the AC configures itself to run in reverse using a pair of pressure regulating valves and a crossover valve to reverse the flow direction. Instead of pumping heat out of the air in the car’s cabin and then radiating it out from the condensor behind the front grille, it draws heat from the outside air, cooling down the condensor pack, then pumps the acquired heat into the AC core, heating the evaporator pack. This requites adjusting the pressure of the refrigerant on each side which is done by a computerized control system.

It turns out that this scheme is much more efficient than using an electrically heated coil. (Although it is much more complex from an engineering standpoint.) AC units have a Coefficient of Performance (C.p.) of about 3x-5x, meaning that for every kilowatt of electricity they consume or mechanical power from the car’s serpentine belt, they can move 4kw-5kw of heat.

Just like an electric soace heater in your house, this would only take a few tens of seconds to start noticeably warming the air.

The heating of cabin air is secondary to the heating of the engine and it’s relevant fluids.

Heating a space (car, room, office etc) relies on air flowing past something hot.

In cars, it is the water that cools the engine that the air must flow past to heat the cabin space. Think how long it takes to boil a kettle. With a fan behind the kettle, the air flowing past the kettle will be cold to start off with, getting warmer as the water heats up.

With a space heater, an area inside the heater is heated up instantly, think like a toaster element. So a fan placed behind a toaster will blow heated air straight away.