Smart & Connected Life Connected Car Tech 67 67 people found this article helpful Choosing a 12 Volt Car Heater Stay toasty warm in your car this winter By Jeremy Laukkonen Writer Jeremy Laukkonen is tech writer and the creator of a popular blog and video game startup. He also ghostwrites articles for numerous major trade publications. our editorial process Facebook Twitter LinkedIn Jeremy Laukkonen Updated September 21, 2019 Robert Millman / Aurora / Getty Connected Car Tech Android Auto Apple Carplay Navigation Tweet Share Email Cars come with powerful heaters that are designed to keep you warm in even the coldest of conditions, but what do you do when your car heater fails? Repairing a car heater can be prohibitively expensive, and 12-volt car heaters are relatively affordable, so it's only natural to wonder if you can get by with the less expensive option. While 12-volt heaters aren't designed to replace factory car heaters, and they aren't capable of putting out the same level of heat, they can come in handy in a lot of situations. It's just important to understand what you're getting into so you can make an informed decision. In order to select the right 12-volt car heater, there are a handful of easy questions that you can ask yourself. These questions will address how you plan to use the heater, which will allow you to effectively choose whether to buy a 12-volt plug-in car heater a larger, hard-wired unit, or whether a regular 120v space heater might do the trick. Considering these important questions will also help you decide what type of heater to select, how much wattage that you’ll need to get the job done, and whether a real universal car heater replacement that taps into the cooling system is what you actually need. When Will You Use the 12-volt Heater? The most important question that you need to answer is concerned with how, and when, you plan on using a 12-volt heater. There are three primary situations where you might use a 12-volt car heater, and each one calls for a slightly different solution. For instance, a 12-volt car heater can be used to replace a malfunctioning factory heating system when the engine is running. However, a 12-volt heater isn’t the right choice for heating up a car when the engine isn’t running. How will the heater be used? To heat the car when the engine is running: You need a 12-volt heater or a battery powered heater for this, although you may be able to use a standard space heater with an inverter if your alternator has enough power to spare.To heat up the interior of the car before driving it: If you can safely get an all weather extension cord out to your car, a standard 120-volt space heater that's designed for use in recreational vehicles might be a good choice. Make sure to get one that's save to use in small spaces.To defrost the windshield before starting the car: This is another situation where a standard space heater could help. Window defrosting can also be accomplished with low powered 12-volt heaters, or even by running your air conditioning depending on the local humidity. Replacing a Malfunctioning Factory Heating System If you only plan on using a 12-volt car heater when the engine in your vehicle is running, then you’re on the right track. Since the engine is running, you can safely run the heater without draining the battery. This is the only feasible way to use a 12-volt heater in a car, and it is also the only way to use an electric car heater as a direct replacement for a malfunctioning factory heater system. Unlike factory systems, which rely on hot coolant from the engine, a 12-volt heater will provide heat the moment you turn it on. However, it will also draw a great deal more power from the vehicle’s electrical system than a factory system that only requires electricity to run the blower motor. It's also important to remember that no 12-volt heater will provide the same amount of heat as your factory heater. If you're looking for a replacement car heater that will provide the same level of heat as the factory heater, then you'll be more happy with a universal car heater replacement that taps the cooling system and replaces the factory heater. These systems provide far more heat than electric 12-volt heaters. Running 12 Volt Car Heaters with the Engine Off If you plan on using your heater to defrost the windshield or warm the car up with the engine off, then a 12-volt car heater probably isn’t going to be a very good idea. Unless you start the engine while the heater is running, the battery may be drained to the point where the engine won’t start. In that case, a battery operated heater may do the trick for defrosting, and a plug-in car heater that runs on 120v will suit your purposes for warming up the vehicle. For more information, check out our full guide to the best portable car heaters. Are There Any Fire Hazards? The next question to ask yourself has to do with the issue of fire hazards, which typically come in the form of combustible materials inside your car. Anything from loose papers to upholstery that isn’t flame retardant can constitute a fire hazard, so it’s important to consider the space that you’re working with before you select a 12-volt car heater. Most 12-volt car heaters are designed to be used in tight quarters, unlike residential space heaters, but every car is different. Use common sense, and consult an expert if necessary. If there aren’t any combustion hazards inside your car, or you can mount a heater a safe distance from any potential hazards, then you have more or less free reign over your choices. You may be better off with an oil-filled heater if there are any lingering questions about combustion hazards. These heaters take longer to warm up, but the trade off is that they don’t create the same type of combustion hazards that you see with other types of heaters. Radiative vs. Convective 12 Volt Car Heaters The two main types of 12-volt car heaters are radiative and convective, and they each have their own strengths and drawbacks. Oil-filled heaters fall into the convective category, and they are the safest to use in cars, trucks, recreational vehicles, and other tightly confined spaces. Convective heaters like oil-filled units transfer heat into the surrounding air, which then rises due to the fact that hot air is less dense than cold air. That causes cold air to rush in to fill the void, which in turn rises up and pulls in more cold air. This cycle is referred to as convection, which is where the name of this type of heater comes from. Since convection relies on a closed volume of air, these heaters work well in vehicles that are sealed up. Although oil-filled convective heaters are relatively safe to use in confined spaces, some convective heaters use heating elements that can pose combustion risks. Radiative heaters also use heating elements, but they don’t warm up the air around themselves. Instead, these heating elements emit infrared radiation. When this infrared radiation hits a surface of an object, it causes that object to warm up. That makes radiative heaters great at providing heat in poorly-insulated environments like cars, but it also means that they won’t actually warm up the air inside your car. Some radiative heaters are also dangerous to use in tightly confined spaces due to the combustion risks posed by their heating elements.