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Most folks probably already know this, but I think it bears repeating that fiberglass is a very poor insulator that supports mold and that loses a significant portion of it's 'R' value when subjected to extreme heat or cold. It's called thermal drift, and it happens when you need it most. This also effects a lot of the foam products, but not to the extent that FG suffers.

Reflectix and the "bubble wrap" core products have an 'R' value of basically 1, and that's just for the air layer that it creates. The Mylar like surface reflects most long wave radiation (those are the frequencies that we feel as heat), but there are other products out there that do the same thing, in the same thickness, but that add a lot more 'R' value.

Something else that needs  some clarification is that Styrofom is a name brand Extruded Polystyrene (XPS) product made by DOW Chemical, usually blue, but they make other colors too. It has never been used to make food service cups. The stuff we know as "styrofoam cups" is actually Expanded Polystyrene (EPS), and the two products have very different properties.

XPS and Polyiso foams are very similar and  both get an initial 'R' boost over EPS thanks to the gas that is used to create the tiny bubbles that form the foam. Problem is, they de-gas throughout the life of the product, causing more of that "drift" mentioned with FG. EPS starts out at a lower relative 'R' rating but its rating remains stable throughout its lifetime. EPS can absorb more moisture more rapidly than XPS, but it can also lose that moisture more quickly too, so if both are kept wet for an extended period of time, the XPS, as well as the Polysio, will take much longer to dry out, so double edged sword.

I've seen a lot of comments about insulated vs. non-insulated floors and where to put what. Looking at a heated van or any vehicle, in the real world, where air is circulating all around it, and most importantly, wind is stripping heat from all sides, above and below. The heat will move like water or electricity. What I mean by that is that it will take the path of least resistance to its flow or movement, so your greatest heat loss will occur at your envelope's weakest point, or in this case, lowest 'R' value surfaces of your envelope.  So if you insulate the heck out of your roof, and maybe not so much the walls, and do nothing with those big expanses of glass in your windshield and windows, the greatest heat loss will be through the glass, and in a van with an un-insulated metal floor, through the floor as well. As a matter of fact, your heat loss will be so huge that the vehicle will very quickly take on the temperature of the ambient outside air. The only thing your vehicle provides then is a way to keep the wind off of you. It's just a matter of too many Btu's leaving faster than your body can replace them.

So if you resort to adding Btu's artificially, you're always going to be spending money to keep warm, and wouldn't we all rather not have to do that? The answer is all math, ya just need to slow that heat loss down to a point where you reach an equilibrium with your ability to keep up. If you reduce it far enough you'll soon find yourself comfortable in shirt sleeves, even with it freezing outside, but that takes a lot of attention to detail.

With insulation covering the glass, most RV and mobile home type single pane windows also provide direct heat loss conduits (that also work like radiators in the summer) because they have no thermal "break" in their frames between the outdoor and indoor environments, so in the summer, something that keeps the window frame from catching direct sun is a big help, and in the winter, something on the inside that gets in the way of the frames wicking heat to the outdoors will help.

The issue of the un-insulated floor is I think best understood if you just look at the effect of wind chill. It works the same on your van as it does on your face, so wind whipping under your vehicle's belly is going to strip heat the same as it does blowing across your glass, walls, or roof. The point being that a uniform layer of insulation throughout is the best solution when pure heating and heat retention is the goal.

In a high heat environment of course that changes a bit, as long as you're not trying to air condition the space, and as long as you don't arrive in the heat of the day and park over an already super-heated substrate. If you're short on dough and just need help hiding from the long wave radiation, the Mylar type covering of the bubble wrap will be a huge help, but so will a couple cheapo "Space Blankets". Better yet the roof rack idea with a space blanket laminated onto a piece of plywood would work even better, since any heat that gets absorbed by the plywood will have air on both sides cooling it, so the sun never touches the roof, and nothing from the plywood can conduct heat since there is no path. In that instance you could probably succeed in eliminating nearly all of the long wave radiation completely, so then your awnings become the next most likely suspect for limiting heat gain from your walls, other than the ambient air temperature itself.

Heating, cooling, and controlling moisture in a big aluminum or steel beer can on wheels absolutely has some unique challenges, but the basics of thermal dynamics are constant, we just have to be observant in addressing what applies where. If I were trying to prepare for both extreme heat and cold possibilities, my goal would be to create an igloo cooler on wheels, with a uniform layer of insulation on every square inch of my living space. With that accomplished you could literally heat your space with a candle (but don't do that 'cuz it'll eat up all of your air!). If you're in a van you might also look at trying to reduce the size of the space that you're trying to keep warm, so maybe a removable bulkhead or plug made of foam board turned into a composite panel (cover with FG screen and paint both sides with latex paint) that could be used to close off the front from the cargo area? Just spit-ballin'...

Reading recommendations for operation of combustibles in enclosed spaces to try and keep up with large heat loss deficits completely creeps me out and makes me worry for peoples' safety - I don't care how many times you've gotten away with doing it. Whether it be alcohol, propane, butane, or any other fuel. Better insulation all around will keep you comfy with none of that, so cheaper, safer, and more comfortable in the long run, plus you save space by not having to lug around a heating solution.

And for the record, 100% complete combustion rarely occurs with any of the stoves being used, so remember, the first product of that problem is carbon monoxide, which you can tolerate in low doses for a long time, but the effects can become cumulative and extremely debilitating short of death. Also, the "alcohol" fuels often contain all sorts of other compounds, none of which are good for living things. Here's a quick list of Crown Fuel constituents (REI sells them):

Methanol 65% - 75%
Ethanol 20% - 30%
Isopropanol 0 – 5%
Methyl Isobutyl Ketone 0 – 1%

By-products of incomplete combustion of most of these is also not healthy in any way.
well said
Polyiso has the highest rated R value of commonly available foam panels, but that value goes down with temperature. If you are protecting yourself from cold weather, XPS is actually better:

When boondocking in hot weather, keeping the sun off your van and especially off the windows makes a huge difference. Burning Man attendees swear by Aluminet, which is a woven tarp similar to what some truckers use but with a reflective surface. It lets some wind through but keeps the sun off. You can extend it over your van by using poles, or simply drape it over your rig and tie it down if you don't care about your paint job too much.
A typical human body heat is about 300 BTU. About the same as a candle.

Not enough to do anything useful in a volume of air the size of a van.

Ditto for those "flowerpot-candle heaters" one finds all over YouTube.

Insulation works by trapping heat. It won't do anything useful without a heater.
Great post Y to clarify the basics and important aspects of insulation. Reduce heat loss/ gain, improves the indoor environment and comfort.
Reflectix works to minimize heat buildup for windows in the sun, but as real insulation, costly and ineffective. Anyone putting up rolls of the stuff is wasting their money imho.

And if super insulated, you can reduce the amount of heat or cool required to maintain comfort, by allot. Maybe 50-75%?
Many years ago, This old house did a program on super insulated homes in Minnesota. They used a water to air heat exchanger fed by the hot water tank to heat the whole house. That was it.
While a tea candle might not do it in a rig at -30, will certainly take smaller and, for shorter periods of time, to heat or cool to maintain comfort levels.
The importance of insulation and reasonable cost can not be said enough as Y said.
And a super insulated approach requires a ventilation system in conjunction. Cheap 12v computer fans could be used.
In my van which I insulated throughout, I feel cold in the lower section. I never gave the floor much thought, I have at most 1/2 inch rtech in some areas. After reading your article I'm adding another couple of layers of rtech. I suspect in the summer, thats also where I'm getting some of the heat from.

I agree on your igloo cooler description its what I'm trying to achieve. Even my cabinet doors are made out of foam insulation. The results have been great where I don't need a mr.heater anymore. This morning it was 42 outside, inside my van it was 60 degrees. It still felt cold to me but I didn't need a heater. I add more layers of foam every year, its a never ending job, but everytime I get a few degrees of improvement which is well worth it.

Last year back of van interior

This year added more foam layers and finally added wallpaper. 
Keep it up and there won’t be any room for you!

Sent from my iPhone using Tapatalk
(02-05-2019, 01:06 AM)Yosarian Wrote: [ -> ]Most folks probably already know this, but I think it bears repeating that fiberglass is a very poor insulator that supports mold and that loses a significant portion of it's 'R' value when subjected to extreme heat or cold. It's called thermal drift, and it happens when you need it most. This also effects a lot of the foam products, but not to the extent that FG suffers.

I didn't know that at all and I bet few people do.  Fiberglass was ubiquitous as insulation when I was growing up anyway, and there's still plenty of people using it today.  Thanks for the knowledge!  

That and the rest of your post was super-helpful.  Don't be shy to share, because it's likely most of the forum readers will always be less experienced and technical ones (like me!), and threads remain searchable for good info for years and years to come.
I was told maybe ten years ago that if you had an ice chest/cooler that had 6 walls, each one foot thick, and put in it a gallon jar filled with boiling water, sealed it and put it outdoors in a Wisconsin winter, at some point, you could open it and find the water frozen solid.

This illustrated to me (a SoCal girl) that no matter how much insulation you have, without a CONSTANT source of heat of a certain amount, the temperature inside any insulated container would eventually become equal to the outside of the container.

I think this is one of those Laws of Physics that some people keep mentioning.

The human body produces between 250 and 400 BTUs, the least amount when sleeping. That's about the amount of heat of a 100watt light bulb every hour.

Realistically, I can't see a vehicle being completely,100% insulated. Unless you completely seal off the living area from the cab, there are going to be heat leaks at the glass, in the knee and pedal areas, and around the engine.

Inside the van, there is the wall and the ribs. The ribs stand out about 1" from the wall. If you install 1" polyiso (for example) on the wall between the ribs, you will still have cold temps flowing past the polyiso through the metal ribs, into the van. Many people lay another 1/2" thick layer of polyiso over both the ribs and the first layer of foam for a total of 1.5" of foam, perhaps ignoring that the cold is only 1/2" away at the ribs. Others may use 1" polyiso, providing 2" of insulation at the wall, and 1" at the ribs.

But let's assume the best, and say that you have applied 2" of insulation to the entire cargo space of a 1999 Ford E150 van, which measures 110 L x 71" w x 51" h = 398,310 cu in = 231 cubic feet.

12.39 cu ft of air weighs 1 lb (presumably at sea level, less at higher elevations).

It requires 0.24 BTUs of heat to raise the temp of 1 lb of air by 1 degree. By my calculations, that van contains 18.64 lbs of air. That seems to indicate that it would take 4.47 BTUs of heat to raise the inside temp of the van by 1 degree F.

A human body produces between 250 and 400 BTUs per hour, the least will sleeping. This is said to be about the same amount of heat as a 100-watt light bulb.

So far, I have not been able to find a calculator which can tell me how to incorporate the various encroaching OUTSIDE temperatures to figure the tolerance of an average human body to cold.

If the outside temp is 32F, how long can a sleeping (or awake) person's own body temperature compensate for the dropping inside temperature without additional heat from another source, like a stove?

Inquiring minds want to know!
Excellent post Yosarian! I would like to add:

Have you ever noticed that windshield sun screens look just like Reflectix? Well that's because Reflectix is made out of the same stuff that most windshield sun screens are made out of. Ergo Refectix is only good for one thing, covering windows on hot days. If you already have a sun screen then don't bother with Refectix and use that instead.

The only other way you could use Reflectix is if you had black or dark colored van you could wrap you van entirely in Reflectix. It would look really bizarre in the blazing sun, but in that specific situation Reflectix would actually work as advertised!

However, if you have a white van that would do almost as good a job with the added advantage that your van won't look like a silver space ship. Seriously though, a white van really will do a far better job then Reflectix.

Everyone understand why this is so? Think about this for a second. If you were to take two vans, one painted white and the other black and put both of them in the hot sun what would happen? The black van would get way way hot, much hotter than the white van. That extra heat that you would feel on the black, that is almost entirely radiant heat. The reason the white van is so much cooler is because the white paint reflects radiant energy while the black paint adsorbs radiant energy.

The upshot of all this is a white van will work better than Reflectix ever could and a cheapo sun screen from autozone will be less cash and simpler because you won't have to cut it to the shape of your window like you would Reflectix.

A note on insulating floors: Heat rises, so it will take the path of least resistance upward. This is important to note. In a cold climate, especially at night, it is very important to cover your windows with something with serious R value! If you don't the heat will go straight out the windows, not the floor. Yes, you are technically correct you would theoretically be correct about losing heat through a metal floor. In reality you would have to have done such a good job with the walls and roof that a Yeti cooler would feel week. Short of that the heat will always find a much quicker way out of the van by going upwards. One idea would be to obtain some Thinsulate clothing grade and cut and sew it into a window cover of some sort. There are many possibilities. Reflectix or a window sun screen will not help at all because they have really bad R-values.

Insulating the van floor is very very important if you want to keep cool in hot weather. The reason is simple, cold does the opposite of heat, it sinks. Thus for example, if you were to turn on the AC in the hot weather, all the cool air will go straight out of the van through the floor. Insulating the floor will be a major improvement(assuming that you did a good job on insulating the van walls and roof).

And finally you made a good point about XPS and polyiso that is also relevant to the insulated floor issue. I've seen a number of people use XPS and polyiso when they insulate the van floors. This is probably a very bad idea because on the floor of the van XPS and polysio have shifting weight on them and that will greatly accelerate the de-gassing and breakdown of the air pockets in the cells. XPS and polyiso if manufactured correctly will last a very long time without any significant de-gassing if they are set in place and you don't touch them. They were never meant to be stepped on! Think about it for a second. I'm pretty sure that using XPS and polyiso for insulating the floor is a bad idea because it they will lose all R value very quickly because of the weight put on them.

Hope this helps...
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