How Much Does It Cost to Warm up a Car, and Does Heat Really Use Gas?

warm up car
How much does it really cost to warm up a car?. Marlon Rucker / EyeEm / Getty

For decades, the prevailing wisdom has been that you should always allow your car to idle and warm up before hitting the road. While modern fuel injection systems and emission controls have rendered the imperative to warm up your engine a thing of the past, this issue is still a contentious one.

On the one side, you have groups like the Idling Gets You Nowhere campaign and the Hinkle Charitable Foundation arguing against ever idling from an environmental standpoint, and on the other side you have folks who have to deal with sub-zero temperatures all winter.

While a car that is idled will undeniably produce more emissions than one that is simply driven, the fact is that it's both undeniably unsafe and downright uncomfortable to drive a car without idling it first once the mercury has dropped far enough.

Does Running a Car Heater Really Use Gas?

Before really digging into the numbers of how much it costs to idle a car, it's important to answer the question of whether or not running a car heater actually uses gas.

While there's no mistaking the fact that running air conditioning uses gas, and will reduce fuel economy, the fact is that cranking up your heat absolutely will not reduce your fuel economy. When you consider the costs of warming up your car in the morning, the important consideration is the fact that the car is idling, not that the heater is running.

In fact, if you start up your car and let it idle, it will use the exact same amount of gas whether the heat is on or not.

But it absolutely will use gas as long as the engine is running, even if it is just idling.

Although idling a car definitely uses gas, it's important to note that there's a difference between using a car heater when a car is idling and using it when the car is being driven. Running a car heater while the car is idling will effectively warm up the interior of the car at the same time the engine warms up, but there is no extra cost associated with turning the heater on versus simply running the engine.

This is due to the fact that car heaters, in virtually all cases aside from electric vehicles, utilize waste heat from the engine that can either be dissipated into the atmosphere or used to warm up the interior of the car.

Is It Necessary to Idle a Car Before Driving It?

In most cases, and with most vehicles, idling to warm the engine up isn't strictly necessary. Older vehicles that lack fuel injection and modern emissions controls are the main exception to this rule, so you're typically going to be just fine to jump in any modern car, crank it over, wait ten or twenty seconds, and go.

Other exceptions include situations where you're dealing with especially cold temperatures, in which case a block heater is a much better way to prevent engine damage than simply idling an engine that's been sitting in sub-zero temperatures all night.

Of course, all the block heaters and environmental hand-wringing in the world can't change the fact that it's both unsafe and uncomfortable to jump in a freezing car and just hit the road.

Although a block heater will heat up the engine to a certain degree, it won't do anything to warm up the interior of the car or defrost the windows. To deal with those issues, you either need to idle your car or rig up some kind of portable heater (ideally on a timer or with a thermostat).

How Much Does Idling a Car Cost?

If you're going to take some of the chill off by idling your car (either via a remote car starter or by actually trudging out into the freezing cold), you might be curious about how much it's actually going to cost.

While it's impossible to give a single figure that will work for everyone, due to all of the different factors that will affect how much gas you actually burn, the Argonne National Laboratory performed a study on three different engines, including a 1.8L Honda Civic, a 2.5L Ford Fusion, and a 3.6L Chevrolet Malibu.

For each of these engines, idling for 10 minutes will consume roughly:

  • 1.8L Honda Civic: .026 gal
  • 2.5L Ford Fusion: .082 gal
  • 3.6L Chevrolet Malibu: .14 gal

According to AAA's Fuel Gauge Report at the time of this writing, the current national average for regular gasoline is about $2.49/gal, which means that idling your car for ten minutes is going to cost you somewhere in the neighborhood of $0.06 - 0.34.

Since fuel usage during idling tracks linearly with time (according to the ANL report), you can use those numbers to guestimate your costs if you idle for a longer or shorter period of time. If you have a larger engine, then you have to figure that it will cost more.

While a quarter here or there is unlikely to break the bank, it's easy to see how the costs of idling could add up over time, especially when gas prices trend higher.

Of course, it's also important to remember that it's actually illegal to leave an idling car unattended in some states.

Is It Cheaper to Use a Space Heater to Warm up a Car?

According to the latest figures, from the US Energy Information Administration, the national average price of electricity per KWh is about $0.132 at this time. That figure fluctuates up and down from time to time, but it's close enough to get an estimate, and you can check out the current figures for an exact number if you prefer.

Let's say you find a 1000W plug-in car heater, and you run an extension cord out to it (either ganged to your block heater, or through other means), and you want to use it to heat up your car and defrost the windshields. Even if you leave it running for a whole hour, it's still only going to cost you about 13 cents (give or take, depending on where you live.)

What that means is that unless you're driving a car that has an engine in the 1 liter range, it's actually cheaper to run a space heater for an hour than it is to idle for ten minutes.