Understanding Insulation in Your Van
(On January 22nd I’m moving back to my Ehrenberg camp with probably a fairly large group of people from the RTR. Everyone is welcome to join us! At the bottom of the post are maps to that camp!)
I should have written about insulation earlier in the winter, but better late than never! I constantly encounter misunderstandings about insulation so I want to spend some time on the science of it as well as the practical application. But before we do I want to make it clear that even more important than insulation is sealing your car, van or RV against air-infiltration. Nothing will make you colder than moving air and even if you insulate but air seeps in and blows around you will still be cold. Before you insulate take time to work on all the seals around the doors and windows. Do whatever it takes to keep them tight. But that’s a subject for another day.
The above graphics illustrates the three main kinds of heat that impact us as vandwellers:
Radiation: heat radiates from the heat source and when it strikes an object transfers the heat to the object. The classic example of this is the sun. Heat leaves the sun, travels through space and hits our atmosphere, travels through it and when it hits the your skin, or the metal skin of the van it dumps the heat into. Or, it hits the glass windows, travels easily through it and dumps its heat directly into the van. Radiation only occurs through air or a vacuum.
Conduction: Occurs when heat is transferred from a warm body to a cool body through some solid material between them. This is what happens in the winter when you have a heater on inside the van. The air inside the van is warm so it wants to get through the walls to the cool air outside. It travels through the walls as conduction. To stop that, you need an insulation with a high Resistance to heat transfer, commonly called an R-value.
Convection: occurs when heat moves through a gas or liquid body. So studying temperatures in the ocean is studying convection. In your van, the warm air rises to the top and pools on the ceiling and the cool air falls and pools on the floor because of convection.
Radiant Barrier: A radiant barrier reflects radiant heat away from an object thus keeping it cooler. A perfect example of this is putting Reflectix in your windows. When the radiant heat from the sun hits it, it bounces away keeping your van much cooler. Or, on the inside of the van, when the radiant heat from your Mr. Buddy hits it, it bounces back into the van. However, if there is anything on top of the Reflectix, it losses all its radiant value and is worthless. If it’s directly against the metal skin of the van or paneling on the inside, the metal and paneling absorb the heat and the Reflectix can’t reflect it. Radiation only occurs through a vacuum or through a gas, not through metal or wood. Heat moving through a solid object is done by conduction and a radiant barrier is worthless against conduction.
R-Values: All materials Resist the conduction of heat through them. Some do it extremely well and some do it very poorly. We assign a number value to them of their Resistance to the conduction of heat. The higher the number, the greater the Resistance. In this table I give the R-value of some common insulations. For the money, nothing beats styrofoam, although if you can afford to spend just a little more, Polyiso is far better.
WHERE TO INSULATE
It’s a physical law that whenever bodies of air meet each other that the heat in one body wants to migrate to the cold in the other body and the greater the difference in temperatures the greater the force is to drive the heat into the cold. So the greater the difference in temperature, the more force to push the heat through the insulation therefore the more Resistance you need to stop the conduction of heat. Put simply, you need more insulation in hot areas than in cool areas.
Let’s imagine a scenario; it’s 20 degrees outside so you turn your Mr. Buddy Portable Heater on to warm up. Because of Convection the warm air rises, in an hour the inch of air at your ceiling will be 110 degrees, where you’re sitting in the middle of the van will be 80 and the floor will still be 30. The difference between the inside hot air and the outside cold air at the ceiling is 90 degrees so there is a lot of force to move the heat across. The difference in the middle of the van is 60 degrees so there is a fair amount of force to move the heat across and there is only 10 degrees difference at the floor so there is very little force to move the heat across. Based on that:
1) Insulating the ceiling is very, very important.
2) Insulating the walls is important
3) The floor is unimportant. Insulate it only if you have the extra money.
Based on the science, what I did was put 2 ½ inches of insulation on my ceiling, one inch on my walls and none on the floor. The only time insulating the floor pays off is if you devise a fan system to pull the heat off the roof to the floor. That wouldn’t be hard with some PVC pipe and a computer fan. But because I don’t do that so I didn’t insulate my floor. I follow a four part strategy for the floor:
- I put down throw rugs in the traffic areas so my feet don’t touch a cold surface.
- I keep my feet elevated out of the cold.
- I wear dry, synthetic socks and add a second heavy pair of wool or synthetic boot socks over them.
- When it’s very cold, I wear down booties.
WHAT TO INSULATE WITH
Don’t Miss-Use Reflectix. This is where I see the most confusion, particularly with people totally miss-using Reflectix. Reflectix is a Radiant barrier and works extremely well against radiant heat because it not only shades, it reflects the heat away. So if you want to keep the suns heat out, it’s a perfect choice. However, it has an extremely low R-Value so it does almost no good against conducted heat.
The problem is there must be an air space of at least ¾ inch or more for it to work. Remember, radiant heat only occurs through air or a vacuum and not through solids, so if your Reflectix is directly against the side of the van or plywood or paneling, it has no value as a radiant barrier and has a very low R-value of 1 per inch. Some people refuse to believe that so here is a quote confirming what I’ve said
If an air space is not present or is too small, heat may be able to conduct through the radiant barrier. Since the metal in the radiant barrier is highly conductive, the heat transfer would all be through conduction and the heat would not be blocked. According to the US Department of Energy,“Reflective insulation and radiant barrier products must have an air space adjacent to the reflective material to be effective.”
If you put Reflectix in a window, the radiant heat from the sun easily passes through the glass, hits the shiny metal and is easily passed back outside through the glass. Reflectix is the perfect thing to put in a window! With an air gap, it works well in the wall next to the van sheet metal. Without the air gap it’s money thrown away.
I recommend you NOT put Reflectix on the walls of your van and buy an extra 1/2 inch of styrofoam or Polyiso instead.
Use a High R-Value product to Stay Warm in the Winter. In the winter, heat loss is almost all through conduction and the way to stop it is with high R-value insulation. Because we live in such a small space, we need the highest number we can get so we lose the least amount of space to insulation. By far your best option is Polyisocyanurate commonly referred to as Polyiso. It has an R-value of 6 per inch and if you get the foil-faced kind it’s 7 per inch. If you can’t find it, or it’s too expensive, your next best choice is plain old white, pink or blue Styrofoam. It has a good R-value, is relatively cheap and is very easy to work with. In every way the Polyiso is a little better, but Styrofoam will work just fine on a budget. The Pink or Blue Styrofoam are better than white but not as good as Polyiso. Whatever you get, try to get it with a reflective foil and it will be your vapor barrier and radiant barrier together.
I don’t recommend fiberglass insulation for vans. Fiberglass is great in houses but poor in vans for these reasons:
- If you compress it at all it loses its insulation value. Because it has a low R-Value, you will be tempted to get more and compress it.
- It takes too much space inside the van. The most commonly available size is R13 which uses 3 1/2 inches of space. Put that on both walls and you lose 7 inches of precious space in the van! Consequently, you’ll probably compress it and lose much of its R-Value. I strongly recommend Polyiso instead which is a type of styrofoam. It is R6 per inch so 2 inches on each wall gives you R12. Much better!! I just used 1 inch and think that is enough unless you are in extreme cold. I only lost 2 inches of interior space.
- It can sag because of the vibration of the van.
- The shaking can make it give off fiberglass particles that make you itchy and get in your lungs.
WHEN YOU MAY NOT WANT TO INSULATE
If you live in cold country and cold is more of a problem than heat then you should insulate, you’ll be glad you did. On the other hand, if you live in a very hot area and cold is a minor issue, you may not want to put in insulation. While it’s true that the insulation will slow down the heat getting into the van, eventually it will get in. If it’s a 100 degree day, and you aren’t running AC of some kind, by the end of the day it will be 100 degrees inside. Once that heat is inside, the insulation won’t let it out and by bed time it will still be uncomfortably hot, probably too hot to sleep. In that case the insulation is hurting you more than helping you because without the insulation the van would have cooled off much better. In that case, it you’re in Florida where heat is a big problem and cold is a minor problem, don’t insulate.