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DIY Van Insulation For Hot Weather

Surviving in hot weather and cold weather are two completely different processes. The bottom line is that vans have a lot of space and material constraints that make them less able to handle the temperature extremes that houses can. Insulating your van for handling cold weather in many ways makes it less comfortable in the heat.

When it comes to preventing heat inside a vehicle, it is helpful to understand the three types of heat transfer and how they relate.

Areas of Focus

Protecting windows from radiant heat transfer • Methods to use when insulating the walls • Van flooring insulation • Vent fans and airflow • Awnings and roof attachments • Additional tips for staying cool

Protecting Windows From Radiant Heat Transfer

In a van, direct sunlight radiation through windows will warm up the car more quickly than any other process. Reducing this will drastically reduce how quickly your van heats up.

Infrared rays from the sun (radiant heat) pass through the windows, and can be reflected right back out. Shiny materials like aluminum, Reflectix, or Infrastop, like a mirror,  will reflect the heat.

To prevent heat from the sun:

  • Cover the windshield with a reflective sunshade
  • Cover passenger, side, or back windows with a reflective material
  • Install dark tint to reduce the sunlight passing through

Reflective windshield covers can be bought online and will make a big difference in the amount of heat that enters the vehicle. For smaller side windows, a roll of Reflectix, or Infrastop can be cut to size and placed over the window when parked.

Three types of heat transfer and how to prevent it in a campervan

Homemade window covers

Custom window covers can be created by using Reflectix on one side, carpeting or cloth on the other, and a little bit of insulation batting in-between. This design allows for the shiny side to be facing out in the summer, and the reverse effect during the winter (reflecting interior heat back in).

Window covers can be held up using Velcro, snaps, buttons, ties or simple press-fit.

Insulating Van Walls For Hot Weather

This is disappointingly easy. For hot weather, in most cases you don’t want to have an insulated van. There is a bit of misinformation perpetuated around the ‘net here. And lots of unnecessarily complex air gaps and layers of multiple materials trying to fight basic rules of thermodynamics.

hot weather van insulation for a campervan conversion

Heat issues with standard insulation

Insulation is like wrapping a sleeping bag around your van. If it’s hot out, the last thing you want is a sleeping bag that you can’t get out of.

There are some compounding issues that can be broken down to understand this:

  • The function of standard insulation is to slow the transfer of heat. With insulation, the van takes longer reach the ambient temperature. If it’s 90° outside, and your van is 70°, it might take an hour two to reach the outside temperature. So while your van might be more comfortable at 10am, it’s still going to get hot by early afternoon. There’s no way around this other than adding significantly more insulation (6-12″ thick like in a house). Adding insulation in a van is just fighting for an hour or two of mid-day comfort. If it’s hot outside, then eventually it will be hot inside the van.
  • The downside to this is that when it is more critical to have a cool van- for sleeping- it takes longer to cool down. If your van is 90° inside, then as the outside temp reaches 70°, it will take longer to cool down.
  • This isn’t counting all of the heat sources in the van. Your body puts out heat. Your fridge, computer and power brick put out heat as well. If you’re cooking: heat. So you now have more heat in the van than outside, and it’s being trapped in by insulation. There’s also heat stored in the thermal mass of all the stuff in the van. If you have a jug of water that has heated up during the day, it’s going to be releasing that heat over the course of the night.
  • These problems are all exasperated if you’re using solar power on the roof. Rooftop solar means that to charge your batteries you will need to park the van in the sun. This will make the van hotter than the ambient temperature, like a solar oven. If it’s 85° outside, it will be 95° inside the van parked in the sun. The insulation will reduce this effect a little, but not enough to make a difference. You might hear the argument that “the panels will shade the van”. Not true. They shade part of the van. Even if you have 1000W of solar panels covering the whole roof, other side/s will be soaking up all that glorious sun heat. Another thing to note is that solar panels  trap a little of the heat that is radiating off the roof of your van if it’s hotter than the ambient temperature. So the “roof is shaded” helps a bit, but definitely not more than parking the whole van under the shade with no panels. It’s similar to the difference between you wearing a wide brimmed hat in the sun and you standing in the shade.

Keep in mind that  this doesn’t mean you shouldn’t insulate your van. With good ventilation, you can mitigate most of the effects of the heat buildup. It just means that insulation isn’t helping your van in the heat and should only be done if you are planning on lots of cold weather.

summer camper van insulation to stay cool

What about radiant barriers (Reflectix) in the walls?

Preface: this is based on some conjecture on my part, so take it with a grain of salt. But let me walk you through why I think using Reflectix in the walls is a losing battle. The ultimate purpose of this material is to reflect radiant heat outside to keep it from getting in. There are a few issues with this.

  • On a practical note, Reflectix is hard to install because you need an air gap with minimal surfaces touching the reflective (hot) side. This means that you must essentially build a box within your van that’s not touching the hot outer walls. Any time you attach Reflectix to an outer wall, you are creating a thermal bridge and are you reducing the effectiveness of the barrier. You can use materials like foam that reduce this thermal bridging, but the effect is still there. This makes it hard to attach household things to the walls of your van. To get the rated R-value on HVAC installations, Reflectix is wrapped on top of a series plastic standoffs that are attached to the ductwork which, consequently, is time consuming and rarely done properly in household installs.
  • The radiant heat you are blocking is coming from your van walls. The walls are heating from the sun and outside environment. Then they are radiating heat into the air gap between the van wall and the insulation. Then your Reflectix bounces that heat right back into the van walls. The radiant energy doesn’t magically just disappear once it’s been reflected. You now heating your van walls from both sides and heating up the air in between the two. Air doesn’t hold much heat, so the net gain of Reflectix is still positive, but not nearly as much as if that heat wasn’t trapped by the exterior van walls.
  • Adding a radiant barrier is simultaneously adding a vapor barrier. Your van walls aren’t breathable and Reflectix isn’t either. Stacking these vapor barriers is bad practice because if moisture gets in between the two- which it inevitably will- it won’t get back out easily. It will be trapped in the warm air in between the barriers and you’ll develop a mold problem sooner than later.
Using Reflectix for a DIY campervan conversion insulation

In summary, radiant barriers are minimally effective and take a ton of work with some downsides. Standard insulation will hold your body heat and the hot van interior in more, especially if it’s sitting in the sun.

The most effective way to be comfortable at night in hot weather is to be able to dissipate the interior heat quicker which is counter to what insulation does.

Insulating The Floor

A surprisingly effective method of insulating your vehicle against the heat is by using proper floor insulation. Due to convection and radiation, hot air will transfer through the floor from the engine and exhaust during driving. This can also happen if you are parked above a hot surface like pavement.

The main goal is to insulate the floor well against conduction. This uses the same techniques and materials as you would for walls in the cold, such as foam with a high R-value. For more info on materials check out this article.

If you’re feeling ambitious and think you’ll be driving a lot, you can add heat shielding material on the floor of your van to reduce heat transfer from the exhaust and engine. More effectively, you can purchase heat shielding for your muffler and exhaust.

Advanced tip: an inexpensive laser pointing thermometer can be purchased to determine which areas of your van are transferring the most heat in. This can help you determine which spots need more insulation, or which areas of the vehicle require the most focus.

Vent Fans And Airflow

camping in a conversion van with a maxfann vent fanCovering window with reflectix
@faroutride |

Appropriate airflow makes a big difference in the comfort of your van. To make airflow work at least two openings are recommended: one for air intake and one to pull air through. The further away you place these openings, the more airflow you will get throughout the vehicle.

An example of poor airflow would be having a vent fan in the cab (above the driver seat) paired with opening the driver’s window. Air will flow between the two but you will not get fresh air in the back of the vehicle.

If you have a vent fan in the cab area and open the back windows, you will get air moving through the majority of the van. To get the most airflow, consider opening different doors and windows throughout the day.

Depending on where you reside, bugs may become a major factor in your ventilation flexibility. Options such as creating custom window screens or purchasing large bug nets for the side and back doors are necessary to stay comfortable.

Action Items: For proper airflow:

  • Open doors and windows
  • Install a fixed vent fan in your vehicle

Read our post: best roof vent fans for van life

If you are concerned about installing a roof fan, smaller portable fans can be purchased that run off batteries, however they will not be as effective as a full roof fan.

Awnings And Roof Attachments

The roof of your van is going to absorb a lot of heat throughout the day. Placing white plywood or other reflective material above the roof will reduce the amount of heat that can get inside.

If you park in one place for extended periods of time, consider hanging an awning or tarp above your vehicle as a semi-permeant fixture. Being able to park your vehicle in the shade will make a big difference in the amount of heat that reaches the van.

Attaching an awning to the roof-rack or side of your vehicle will give you a shaded area to hang out in the heat. We installed an awning so we could sit outside in the rain, but have found it to be much more useful in hot weather.

Hot weather campervan conversion insulation with an awning

Additional Tips

As van dwellers, we recommend following the weather for maximum comfort. If possible, head north during the summer, or to a higher altitude. Try to park in shade and face north if possible. This will give you the least amount of direct sunlight on your large windows.

Spend the day somewhere cold like shopping malls, libraries or museums. Limit activities inside the van such as cooking.

It may sound counter-intuitive, but on hot nights it is often more comfortable to sleep outside. We spend a lot of our time on campground or BLM land and keep sleeping bags and a small backpacking tent in the van. We’ve found thatsleeping in a tent is more comfortable than inside the van if we’re caught in a heat wave.

For more tricks and tips read our post: tricks and tips to keep cool in the summer

Air conditioners, swamp coolers, and other active cooling

You may be asking why no one has ever installed an air conditioner in their van. The truth is, people have. It is possible to install an air conditioner, but it is not practical unless you have a generator or shore power. An air conditioner takes an enormous amount of power to run.

With solar power, you can run an air conditioner but it would need so many solar panels and batteries that it is not practical for most people. This van dweller was able to do it with 1000W of panels, 2000W inverter and 780 ah of battery. These things get pretty pricey and bulky, but for those building a sprinter it isn’t out of the picture.

Swamp coolers work by evaporating water with a fan that creates a cool airflow. Because of the evaporation process they do not work in humid environments. Additionally, they require a decent amount of power to run the fan and a water source.

DIY swamp coolers that you see online do not work adequately in small spaces because of how quickly the air gets saturated with moisture and the lack of effective evaporation surface they are usually built with. For these reasons, it is easier to employ the other cooling techniques found in this article.

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