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.
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Leaving a space heater in an unattended vehicle can be a fire hazard. While some residential space heaters can be used in vehicles, they are not designed for that purpose, so use them 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 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.
I'm sick of frosted windows and 2 inches of ice on the car each morning, and I don't have an auto starter so I have to go outside ahead of time if I want to start the car, which normally does not happen as I don't really want to be going outside in -30 winds straight out of bed, I'm already cold enough and just want to get into the scalding hot shower. Also starting the car ahead is just a big waste of gas and creates lot of pollution, so this is also a "green" project if you will.So I've been toying with the idea of finding a way to run electric heat to the car and have it on a timer so it starts automaticly a few hours before I leave.I'd have to do a heat loss calculation but I'm guessing I'll probably want at least a 20 amp 240v receptacle and something like this: http://www.canadiantire.ca/AST/brow...RD~0522604P/Mastercraft%2BGarage%2BHeater.jsp Another option would be a 120v / 1500w oil filled heater which would be safer, but don't know if that would quite cut it.They do sell heaters made for cars, so how are those normally installed? Guessing since they are such low wattage they can be safely set on the dash... but they don't really put out enough heat to melt ice.Also any suggestions on how to run the power from outside to inside the car in a way that is easy to plug/unplug from outside? Is there a standard way to do this or does it really depend on the car model/how it's built? Car is a 98 Buick Lesabre. Idealy it would be nice to have the block heater on the same power cord but it will probably be easier to make this a separate cord especially if I get into the 240v range. I know my stuff when it comes to the actual electrical work, I just don't know my way around the internals of a car. Really I'm hoping I can get away with something in the 1800w range so I can use a basic, cheap 120v timer but somehow I doubt it.I'm sure I'm not the first person to do this, but I can't seem to find anything online about someone who has done this safely.