Are 12V Defrosters a Better Option for the Winter?

What's the best way to defrost a car's icy, fogged up window?

Driving in the winter with a broken defroster can be a nightmare, especially if the cause is a broken or bypassed heater core. The last thing anyone wants before a long commute is to stand in sub-zero weather, scraping diligently at a thick layer of windshield ice, only to climb inside and find the window all fogged up.

In such cases, the only solution is to fix the defroster, whether that means replacing a leaky heater core, a rear defroster heater grid, or an entire window. Repairs like these can be pricey, and suffering through a long, cold winter can look less and less onerous as those dollar signs stack up.

The Problem With 12V Defrosters

There are two main issues with 12V heaters and defrosters, and both issues are related to the way that these devices work. The first has to do with the power supply, which is usually going to be the cigarette lighter socket.

Since cigarette lighter sockets and 12V accessory outlets are usually fused at 15A or less, you can't run a very powerful heater from these. And since 12V defrosters rely on heat to work, you won't see the same results that you used to get from your HVAC system before the heater core broke.

The other issue is related to relative humidity and the fact that dry air absorbs more moisture than wet air. This is why you can defog a windshield with a car that has a broken heater core as long as the A/C works. The air conditioning dehumidifies the air that passes through it, which allows it to absorb moisture from the windshield.

Since 12V defrosters don't have that ability, the air that these defrosters blow on the windshield has the same humidity as the rest of the air in your car. The only difference is that it's lukewarm instead of freezing.

Less Effective Than a Hair Dryer?

To visualize why 12V defrosters aren't great at defogging, it's useful to compare one to a device most people are familiar with: a hair dryer.

While there are many 12V defrosters out there, a typical model that's designed to plug into a cigarette lighter only puts out about 200 watts or so. By comparison, a hair dryer is rated at around 800 to 1,000 watts.

Does that mean that you're better off running an extension cord and defrosting the windshield with a hair dryer? Technically, sure, but if you're running a cord anyway, you also have the option of using a regular space heater to warm up your car.