I think you mean convection? The snow will stop the wind from carrying away from heat (i.e. convection).

Piled snow will actually cause more heat to be lost by conduction (assuming the snow is actually touching the vehicle and that the interior of the vehicle is warmer than 32F/0C).

HJ

Absolutely! I'd say you're better off even if it's warmer than that. Wind sweeping underneath a vehicle can quickly rob a lot of heat.

Of course, using a snow shovel and working up a sweat would be a bad mistake to my view. But if you can get snow protection without otherwise compromising your situation, then snow wind breaks or insulation is the way to go.

HJ

As long as there is snow blowing on the car and/or piled up against it, 32 F / 0 C will be a magical upper threshold for the metal outside of the car. It can get colder, but it can't get warmer - melting snow is a tremendously effective cooling agent.


So - I certainly wouldn't bother with piling up snow around the car if the temperature was not too far below 0C / 32 F.


If it was, say, 0F / -17C, packing the car into a big snow pile could raise the metal outside temperature up to the melting point. Which in this case is a huge improvement. And it would get your car out of the wind. But you can't really pack the whole car - you'd want to leave at least a door or window free. Still, keeping 80% of the outer metal surface at 32F/0C will substantially reduce the heat loss.


The drawback is that it would involve moving large amounts of snow. And it would create problems when you want to move the car again. You will have a crust of ice hard snow around your car. Removing that isn't fun.


Sleeping bags rated for the outside temperature seems like much less hassle. Just sleep through the whole ordeal. And food and (hot) water - you need calories and (preferably hot) liquid or you'll freeze.

IMO long-burning multi-wick candles are a good option. When selecting them it helps to understand that the listed time is only valid with a single, and quite well trimmer, wick. I figure about half the listed time and then divide again for more wicks. For example a 120 hour candle can be reliably estimated at 60 hours for a single wick burning and 30 hours with two going. Yes, you will almost certainly get more run time that this very conservative estimate tells you but that extra is your reserve and safety margin.

I don't know about a 'stack' but two or three would be a reasonable investment. Reasonably priced at less than $9 at Best Glide (no affiliation):

http://www.bestglide.com/Nuwick_120_Info.html

These long burning tinned candles are quite handy. They store pretty well. As long as you keep the right-side-up, so the wax doesn't slump in summer heat, they seem to remain usable for many years. It is also a good idea to take the spare wicks and other accessories out of the tin and tape them to the bottom of the tin inside a plastic bag. Exposed to extreme summer heat I've seen the spare wicks with their tin discs start to sink into the wax. IMHO it is better to leave only the wax in the tin so the accessories are always at hand.

There are a few items that make using these candles easier:
A folding sheet-metal stove that is intended for use with Sterno. Sure beats having to hold a pot.

One or more 12" ceramic tiles or pieces of plywood wrapped in aluminum foil give you a heat resistant place to set up the stove, or place a hot pot. A hot pot can seriously damage upholstery and the plastic of many vehicles.

A piece of plywood. 16" by 24" seems to work well but adjust for your needs. This has to be padded with wood blocks or other material to fit the seats in your vehicle so it rests in a level and stable manner on the topography of the seat contours. It helps if you maintain some rocker in the design, and/or spare blocking, so you can level the surface if the vehicle itself is not level. A non-slip surface and fiddles, raised lips, around the edges help keep things from sliding off. This is your general work surface. A place to set up cooking. A surface to work or play cards on.

These tinned candles give you heat (without having to run the engine) light, a method of melting snow for water, the ability to brew up hot drinks, and do some light cooking.

While you're at it a painter's canvas drop cloth is useful for keeping the food, wax splatters, and other crud associated with survival in a vehicle, off the upholstery.

I've got a beeswax survival candle from Pheylonian products. If I'm stuck in a confined space I'd rather have a clean burning candle (with windows cracked of course). I've got an Altoids alcohol stove too but the candle is specifically for warming up the car. Also have a +40 sleeping bag w/fleece liner, extra clothing, tarp, food, etc.

Sterno.

Art -- Thanks for tips on long burning candles. Those sound good. Tim

Just remember that any open flame is a potential source of carbon monoxide, so be sure to ventilate. Now I will get off my soapbox.....

I'm suprised no one mentioned chemical heat packs (12hr.) and blanket sacks. In our cars we keep the plastic and foam rescue blankets, chemical heat packs and the Nu-Wick 120hr. tinned candles.

Re: Sterno.

Sterno, jellied alcohol, can be used and can be a major benefit. But there are weaknesses that have to be worked around. Effective storage depends on the containers remaining sealed. Any leak will allow the alcohol to evaporate. The old style paint-can seals were pretty good for being resealable. The newer pull top cans with a cheap plastic lid to reseal are only effective for a few days at most. Once opened the can has to be used or it will degrade.

The jellied alcohol only remains jelled when cool. Once you light it a major portion of the fuel, sometimes all of it, turns liquid and can spill. If spilled the alcohol can continue to burn. If you spill liquid candle wax the fire doesn't usually spread because the wax won't burn without a wick. Alcohol fires can be almost invisible.

Trying to melt snow or heat drinks in a vehicle is going to be messy. If you use Sterno you need to be extra careful not to spill it and to make sure it is really out when you think it is. I'm sure it can be done but you might want to invest some effort into manufacturing a stable work surface and a stove or stand to make heating a pot easier. With Sterno you don't want to be trying to balance things.