Your body is your primary heat source when your car’s heater isn’t working. The goal is to trap as much of that warmth as possible while minimizing the ways heat escapes. A parked car in freezing temperatures will eventually reach the outside temperature, but with the right approach you can maintain a survivable pocket of warmth for hours.
Layer Your Clothing Correctly
The three-layer system used by winter hikers works just as well inside a cold car. Your base layer sits against your skin and wicks moisture away. Wool, polyester, or nylon fabrics work best here. Cotton is the worst choice because it absorbs sweat and holds it against your skin, which accelerates heat loss. If you’re wearing a cotton t-shirt and jeans, you’re already at a disadvantage.
Your middle layer is your insulation. Fleece jackets and wool sweaters trap warm air close to your body. A heavy fleece is ideal because it stays warm even when damp and dries quickly. Your outer layer blocks wind and any moisture from getting in. Even inside a car, wind can seep through door seals and windows, so a windproof jacket makes a real difference. If you don’t have a proper outer shell, a trash bag with a hole cut for your head will block drafts in a pinch.
Don’t forget your extremities. You lose heat fastest from your head, hands, and feet. A warm hat, thick socks (again, not cotton), and gloves or mittens are essential. If you have no hat, wrap a scarf or any fabric around your head.
Use Blankets and Emergency Blankets Strategically
A thick wool or fleece blanket is the single most useful item in a cold car. Wrap it around your torso and legs, tucking it underneath you so warm air doesn’t escape from below. Sitting on a blanket or cushion also insulates you from the seat, which conducts heat away from your body surprisingly fast.
Mylar emergency blankets (space blankets) are often marketed as reflecting up to 90% of body heat, but they only work if you use them correctly. The key rule: there must be an air gap between the blanket and your skin. If the reflective material touches your body directly, no heat reflection occurs, and you just lose warmth through conduction. Place the shiny silver side facing outward, toward the cold environment, not toward your skin. And never layer another blanket on top of a space blanket, as that eliminates most of its reflective benefit. Use it as your outermost layer, draped over a regular blanket or sleeping bag that’s already providing insulation.
Shrink Your Heating Space
Trying to keep the entire car warm is a losing battle. Move to the back seat if possible and use blankets, jackets, coats, or even floor mats to create a smaller enclosed space. Hang a blanket between the front and back seats to reduce the volume of air your body needs to heat. The smaller the space, the warmer it stays.
If you have passengers, sit close together. Two or three people sharing body heat under a blanket can stay significantly warmer than each person alone. This isn’t just survival advice from movies. It’s basic physics: more heat sources in a smaller space.
Use Portable Heat Sources
Disposable chemical hand warmers are inexpensive, safe to use in an enclosed space, and surprisingly effective. Standard packs provide heat for 5 to 10 hours, with larger or premium versions lasting up to 12 hours. Place them inside your gloves, in your pockets, or inside your blanket layers near your core. Putting them against your chest, inner thighs, or armpits warms blood flowing to your extremities.
A few candles in a metal container can also raise the temperature of a small, enclosed car interior by several degrees. Tea light candles work well. Keep them in a sturdy holder and crack a window slightly to prevent oxygen depletion. Never leave candles burning while you sleep.
Eat, Drink, and Keep Your Metabolism Working
Your body generates heat through digestion, a process called thermogenesis. Foods high in fats, proteins, and complex carbohydrates take longer to digest and produce more internal warmth. Nuts, peanut butter, beef jerky, cheese, and energy bars are all good options to keep in your car. Root vegetables and ginger also stimulate heat production, though those are less practical as car snacks.
Drinking water is just as important as eating. Dehydration causes your core temperature to drop, which can accelerate the slide toward hypothermia. People tend to drink less when they’re cold because they don’t feel thirsty, so make a deliberate effort. Warm water or a hot drink from a thermos is ideal, but even cold water helps your body regulate its internal temperature. Caffeine increases your metabolism and can temporarily raise your body temperature, so coffee or tea is a reasonable choice if you have it.
Crack a Window for Ventilation
This sounds counterintuitive, but cracking one or two windows just slightly, a quarter inch or so, prevents a real problem: condensation. Your breath releases moisture into the air, and in a sealed cold car, that moisture condenses on every surface and eventually freezes on the inside of your windows. When you finally start the car or temperatures rise, all that frost melts and everything gets wet, which makes you colder.
Worse, in a fully sealed car, moisture buildup can encourage mold growth over time. Cracking a window to the bottom of the rubber gasket creates a small draft that circulates air without dramatically dropping the interior temperature. Some people in extremely cold conditions (below minus 15°F) choose to keep windows fully closed, accepting the condensation tradeoff, but in most winter situations a small gap is worth it.
Carbon Monoxide: The Invisible Danger
If your engine still runs but only the heater is broken, you might be tempted to idle the car for warmth from the engine block. If the tailpipe is blocked by snow, this can kill you. Carbon monoxide from the exhaust builds up inside the cabin with no smell or visible warning. A CDC report on a 1996 Philadelphia snowstorm documented multiple cases: a 4-year-old girl was found unconscious after just 30 minutes in an idling car surrounded by deep snow. A 63-year-old man was found unconscious after roughly an hour in the same conditions.
If you must run the engine, clear the tailpipe completely of snow, ice, and debris first. Check it periodically. Keep a downwind window cracked. Run the engine for 10 to 15 minutes at a time, then shut it off. Even without snow blocking the exhaust, a running engine in a still environment can allow fumes to accumulate.
Recognize Hypothermia Early
Hypothermia begins when your core body temperature drops below 95°F. The early signs are shivering, clumsiness, and difficulty thinking clearly. As it progresses, you may notice slurred speech, slow or shallow breathing, confusion, memory loss, and extreme drowsiness. The drowsiness is particularly dangerous because falling asleep in severe cold can be fatal.
If you or someone with you starts showing these signs, it’s a medical emergency. Call 911. While waiting, remove any wet clothing, wrap the person in dry blankets, and avoid sudden or jarring movements, which can trigger dangerous heart rhythms. Warm the core first (chest, neck, head, groin), not the hands and feet.
Build a Winter Car Kit Before You Need It
FEMA recommends keeping an emergency supply kit in your car that includes blankets, warm clothes, bottled water, non-perishable snacks, a flashlight, and jumper cables. Beyond those basics, a winter-specific kit should also include:
- Chemical hand and body warmers (a dozen packs take up almost no space)
- An emergency mylar blanket (compact and cheap)
- A wool or fleece blanket (more effective than mylar alone)
- Extra wool socks and a hat
- A candle and matches in a metal tin
- High-calorie food like nuts, energy bars, or peanut butter crackers
Check your kit every six months and replace anything that’s expired or damaged. A kit that’s been sitting for two years with crushed granola bars and empty water bottles won’t help you when temperatures drop to single digits.