Using a Space Heater as an Electric Car Heater

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 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, and how much wattage you need to warm up your vehicle. The major pitfalls may 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 120V AC. In most cases, the electrical system in a 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.

When you use a residential space heater as an electric car heater, plug it into an inverter. An inverter 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. However, these heaters provide 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 they draw.

In cases where a space heater is 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 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 up the vehicle 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. 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 use an electric heater in your car, the most important question to consider is whether or not you'll create a fire hazard in the process.

Most residential space heaters carry warnings that all combustible materials must be kept at a minimum distance from all sides of the heater. The specific distance can vary, but it's typically at least a few feet, making 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. Still, you should 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 important to use common sense when installing one of these heaters. Wiring in a 12V heater can 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, 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 poorly insulated compared to homes. That's why your car gets hot when you park it in the sun, and also why it loses heat 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 the interior volume of a small passenger car or truck cab without any trouble, heat loss can start to add up.

If you plan to leave the heater running all night, it may literally run all night, which could lead to an unpleasant surprise on your power bill. A better option is to use a timer, or a thermostat, to limit power consumption.