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?
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.
Driving a cold car in the dead of winter isn't fun, and it can be dangerous if your windows are not adequately defrosted. One of the cheapest and easiest solutions is to plug a heater into you car's cigarette lighter socket. But do these niche contraptions actually work?
Do Portable Cigarette Lighter Heaters Work?
Cigarette lighter heaters are designed to convert energy from your car's electrical system into heated air. The problem is they can only draw so much power, so the resulting heat is paltry. That also means they cannot stand in for a standard vehicle heating system.
Car cigarette lighters are 12-volt outlets and most cigarette lighter heaters can deliver only around 150 watts of energy, which isn't much when compared to a common blow dryer, which usually blasts up to 2000 watts of heat.
In short, cigarette lighter heaters can produce heat, but not much and never in lieu of a traditional car heater. That makes them better suited for very simple things like defrosting the windshield or warming up hands.
Cigarette lighter heaters are too weak to stand in for a standard heating system.
Alternatives to Factory-Installed Heaters
If you’re looking for an alternative to your factory-installed heater, you should consider a 12-volt heater wired directly to the battery with an inline fuse. Another option is a residential space heater plugged into an inverter. Both of those options are limited by the amount of power that your car’s electrical system can put out.
If you’re just looking to warm your car up in the morning before a commute, then a basic space heater might do the trick. A battery-operated heater can also be effective if you merely want to defrost your windshield.
The only true replacement for a factory car heater is a universal heater that relies on coolant rather than an electric heating element, but they are far more expensive and difficult to install than any of these alternatives.
The Problem With Car Heaters and Cigarette Lighters
Cigarette lighter plugs are low in wattage. Most of these circuits are wired with 10- or 15-amp fuses. At 12 volts, even a 200-watt heater will draw over 16 amps, which is enough to pop most cigarette lighter circuits.
Any heater that includes a blower has to dedicate part of its wattage to the fan, too, which is why a lot of car heaters that plug into cigarette lighter sockets don’t have that feature.
Alternatives to Cigarette Lighter Heaters
Here are some workarounds if you don't want to rely on a cigarette light to heat your car.
None of these solutions can serve as a replacement for a factory-installed heater. Always follow installation and use instructions specific to the heater you choose.
Wire a 12 Volt Heater into Its Own Circuit
This option requires you to connect a 12 volt heater to your car's electrical system.
What We Like
Use the right wire gauge for a high current power draw, and install an in-line fuse to properly protect the new circuit.
A 12 volt heater wired into its own circuit can put out far more heat than a cigarette lighter heater.
What We Don't Like
12 volt car heaters, even those wired in this manner, still tend to be pretty weak.
Install an Inverter and Use a Residential Space Heater
This option requires you to wire an inverter directly to the battery, and then plug in a small space heater that's designed for use in your home. Even the smallest residential heater is capable of putting out more than enough heat for a car.
What We Like
Allows for use of more powerful heaters.
Residential space heaters can put out more heat than 12 volt heaters.
Can effectively replace a non-functioning car heater.
What We Don't Like
Residential space heaters consume a lot of power.
Your charging system may not be able to handle even a small space heater.
Most residential space heaters are dangerous to use in confined spaces due to fire hazards.
Either of these options can work if installed properly. Wiring a 12 volt heater into its own circuit is more efficient than using an inverter, but the wiring in an inverter is a more versatile solution since you’ll be able to use it for more than just an electric car heater.