Using a Space Heater As an Electric Car Heater

When and when not to use a space heater in your car

There are two reasons why 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.

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

car electric space heater
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Leaving a space heater in a vehicle unattended can be a fire hazard. While some residential space heaters can be used in vehicles, they are not designed for that purpose, so do so at your own risk.

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 120V AC. In most cases, the electrical system in your car provides 12V 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 car heater system, it’s typically best to use a 12V heater. Although it's technically possible to use almost any residential space heater in a car, it’s both more efficient and less dangerous to use a 12V heater than to plug a 120V heater into an inverter.

In cases where the heater is used as a garaging alternative—to warm the vehicle up prior to a cold morning commute—a 120V space heater may be the better option.

Running a 12V heater when the vehicle is off will quickly drain the battery to the point where the vehicle won’t start, whereas a 120V residential space heater can be plugged into a convenient outlet with a suitable extension cord designed for outdoor use.

The Combustion Question

Regardless of why you would want to use an electric heater in your car, the most important question to consider is whether or not you’d be creating a fire hazard in the process.

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.

Using an electric heater in a car safely isn’t impossible, but you should always use common sense and avoid placing one of these heaters near any combustible objects.

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

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

The issue here is that cars and trucks are very poorly insulated compared to homes. That's why your car gets so excruciatingly hot when you leave it parked in the sun, and also why it loses heat so quickly after you shut the engine off in the winter.

While a residential space heater that’s designed to heat a 10-foot-by-10-foot room is capable of heating up the interior volume of a small passenger car or truck cab without any trouble, heat loss can start to add up.

If you plan on leaving your heater running all night, keep in mind that it may literally run all night, which could lead to an unpleasant surprise on your power bill. A better option would be to use a timer, or even a thermostat, to limit power consumption.