Using a Space Heater as an Electric Car Heater

car electric space heater
The main problem with using an electric space heater in your car is power, but you also can't discount the chance of fire. Sharon Meredith / E+ / Getty

There are two main reasons that you might consider using a space heater as an electric car heater: as a replacement for a malfunctioning HVAC system, or as an alternative to “garaging” your vehicle. Since each of these has its own slightly different goals, there are a number of different issues to consider before you purchase or use an electric car heater.

Some of the most important issues to think about before you buy an electric car heater are whether to use a 120 volt or 12-volt heater, whether it’s safe to use a portable car heater in your vehicle at all, and how much wattage you need to warm up your car.

The major pitfalls you may encounter include power supply bottlenecks, fire hazards, and heat loss.

Residential Space Heaters vs. 12 Volt Electric Car Heaters

Residential space heaters are designed to run on AC power. In North America, that means they run on 120 V AC. In most cases, the electrical system in your car provides 12 V DC, which can fluctuate up or down depending on factors like the battery charge level and the overall load on the system. In order to use a residential space heater as an electric car heater, it has to be plugged into an inverter, which is a device that effectively converts DC power from the vehicle’s electrical system into the AC power that the heater requires.

Some space heaters are specifically designed to be used as electric car heaters. These units run on DC instead of AC, which means that you don’t need an inverter. Some 12 V car heaters can be plugged into a cigarette lighter receptacle or a dedicated accessory socket, but they are only capable of providing a limited amount of heat.

The most powerful 12 V car heaters require a direct connection to the battery due to the amount of amperage that they need to draw.

In cases where a space heater is being used to substitute for a malfunctioning HVAC system, it’s typically best to use a 12 V heater. Although it is possible to use any residential space heater in a car, it’s more efficient to use a 12 V heater than to plug a 120 V heater into an inverter.

In cases where the heater is used as a garaging alternative (e.g. to warm the vehicle up prior to a cold morning commute), a 120 V space heater is sometimes the better option. Running a 12 V heater when the vehicle is off may drain the battery to the point where the vehicle won’t start, whereas a 120 V residential space heater can be plugged into a convenient outlet with a suitable extension cord that’s designed for outdoor use.

The Combustion Question

Regardless of why you’re using an electric car heater, the most vital issue to consider is whether or not you’re inadvertently creating a fire hazard. Most residential space heaters carry warnings that all combustible materials have to be kept a minimum distance away from all sides of the heater. The specific distance can vary, but it’s typically at least a few feet, which can make it difficult to find a safe location to place a residential space heater inside a car or truck. It isn’t impossible, but you should always use common sense and avoid placing one of these heaters near any combustible objects.

Since 12 V car heaters are specifically designed for automotive applications, they are typically safer to use in those applications than residential space heaters.

It’s still important to use common sense when installing one of these heaters, and wiring in a 12 V heater can also introduce additional fire hazards if it isn’t done properly.

Cubic Footage and Heat Loss

When selecting a space heater to use as an electric car heater, it’s important to consider the volume of the air that needs to be warmed up in addition to heat loss. While a residential space heater that’s designed to heat a 10’ x 10’ room shouldn’t have any trouble heating up the interior volume of a small passenger car or truck cab, heat loss can become an issue.