Minimise Heat Loss from Your Campervan in Winter

We all want to be comfortable in our campervans in the winter, so it’s important to maintain a nice temperature inside while temperatures outside plummet. Let's look at winterizing your campervan.

Heat loss from a campervan mainly occurs through:

1. The bodywork
2. The windows

Heat Loss through Van Bodywork

A vans bodywork is mainly made of metal (a good conductor of heat).

When your van walls are exposed to heat, the molecules of the metal begin to move more quickly, they bump into their neighbours and transfer the energy through the metal.

This process happens quickly due to the fact metals are a good conductor of heat. The reason being their atoms are densely packed making this energy transfer much more efficient.

To fix this problem area we need to add insulation materials to the inside of the walls, ceiling and floor.

Insulation materials provide a physical barrier, slowing the transfer of heat to the metal bodywork where without insulation it would easily be absorbed by conduction and expelled from the van.

There are various insulation types on the market and it can be daunting to decide which is best for your application. We’ll talk about the best way to make an informed choice.

Choosing Van Insulation

When choosing insulation we can assess various values (some given by the manufacturer) and decide on the best material for a particular application.

Thermal Conductivity (K-value)

Thermal Conductivity or (how easily heat will transfer through a material), is the most common value given by the manufacturer.

It is an intrinsic property of the material itself. That means a change in thickness of the material doesn’t affect this value. When comparing thermal conductivity values for different insulation materials, the lower the thermal conductivity the better.

You can refer to the manufacturers datasheet to find the thermal conductivity values, they are measured in $W/mK$. You may also see this value referred to as the Lambda value, λ-value or K-value.

For example rockwool states a thermal conductivity of $0.034 W/mK$. In contrast Copper has a thermal conductivity of $398 W/mK$!

As stated earlier, a change in a material's thickness doesn’t affect its thermal conductivity values. However, a change in thickness does affect its Thermal Resistance (or R-value).

Thermal Resistance (R-value)

Thermal resistance or (how well a material resists heat transfer at a specific thickness) is not usually given by manufacturers, simply because its value depends on the thickness of the material you decide to use. It is measured in m²K/W.

Once you know the thermal conductivity of a material you can work out the R-value of a piece of that material at any thickness using this simple formula:

$$Thermal Resistance (m²K/W) = Thickness (m) / Conductivity (W/mK)$$

Let’s work out the thermal resistance of 100mm of rockwool that has a thermal conductivity of 0.034 W/mK:

$$0.1 / 0.034 = 2.94 m²K/W$$

If you are comparing R-values for different insulation materials, the higher the R-value the better, however it is important to make sure you are comparing R values for materials of the same thickness for a fair test.

You want your insulation material to have the highest possible R-value for the amount of space you are willing to let it occupy within your van. Space is a premium inside a van, so you need to find a balance.

Thermal Transmittance U-value

There is another measurement you may have come across, that’s the U-value, also known as thermal transmittance and is measured in W/m²K.

This value is more commonly attributed to buildings, however there’s no reason we can’t apply it to a van. The U-value is a measure of how well a building component, be it a wall, ceiling or otherwise, transmits heat from the inside to the outside.

Obviously we don’t want any component to be good at transferring heat outside so the lower the U-value the better. A lower U-value means the heat transfer through the component is more difficult.

With a low U-value - on a cold day it is more difficult for heat to transfer through the component, this means the component is performing well in terms of keeping the warmth inside, keeping your campervan warm.

U-values for home components in the UK are typically recommended to be as follows:

	U-value (W/m²K)
Roofs	0.11
Walls	0.18
Floors	0.13

Now these values are pretty easy to achieve in a house due to the space you have to install a component that will perform well (with a low U-value).

The problem is, in a van we don’t have the same luxuries of space, we are also restricted by the internal structure of the van which makes it difficult to add all the insulation we would like to.

To work out the U-value of a component (a wall for example) in your van, it’s actually pretty simple and if anything it’s interesting to see if you are getting anywhere near the values recommended for a house.

We’ll first need to know the R-value for each layer of material within the component, we know how to work that out from earlier. Here’s a recap:

$$Thermal Resistance (m²K/W) \\ = Thickness (m) / Conductivity (W/mK)$$

Once we have all the R-values we then need to calculate the total resistance Rt using the following formula:

$$Rt = Rsi + R1 \\ + R2 + R3 + Rse$$

Finally, once we know the total resistance we can calculate the U-value using this formula:

$$U = 1 / Rt$$

You might be wondering, what is Rsi and Rse?

Rsi is the internal surface resistance and Rse is the external surface resistance.

I’m going to use the following Rsi and Rse values:

	Rsi	Rse
Roofs	0.10	0.04
Walls	0.13	0.04
Floors	0.17	0.04

My van walls are made up of the following layers of material, I’ve worked out the R-values for each using the formula we looked at earlier:

		Thickness (m)	K-value	R-value
R1	Steel bodywork	0.001	50	0.0002
R2	Rockwool	0.100	0.034	2.94
R3	Pine tongue and groove	0.015	0.12	0.125

We can now work out the total resistance Rt of my van walls:

$$Rt = 0.10 + 0.0002 + 2.94 + 0.125 + 0.04 = 3.2052$$

The formula for working out the U-value is:

$$U = 1 / Rt$$

So..

$$U = 1 / 3.21 = 0.31 W/m²K$$

Whilst that’s not too bad, it can be improved, for example let’s say we switch out the Rockwool for PIR insulation board which has a thermal conductivity of 0.023W/mK:

		Thickness (m)	K-value	R-value
R1	Steel bodywork	0.001	50	0.0002
R2	PIR insulation board	0.100	0.023	4.35
R3	Pine tongue and groove	0.015	0.12	0.125

Let’s do the workings again:

$$Rt = 0.10 + 0.0002 + 4.35 + 0.125 + 0.04 = 4.6152$$ $$U = 1 / 4.6275 = 0.22 W/m²K$$

Now that’s getting closer to the recommended values for a home without increasing the thickness of the insulation, great!

Knowing how to do these calculations allows you to explore the different insulation materials available so you can build a compact thermally efficient insulation system for your van.

Important to note

Whilst it’s feasible the layers described above will achieve this U-value, we must consider in reality that there are internal structural elements to a van wall which hampers the installation of a continuous insulation system. There will inevitably be gaps which hinder the thermal efficiency of your van.

Structural beams are a good example, if left untreated they will act as a thermal bridge, reversing all the hard work of the insulation installed either side of them.

To improve this a thermal break must be added, normally a closed cell foam, it won’t have a great R-value but anything is better than nothing.

You can install the best van insulation in the world, but leave the thermal bridges untreated and all your efforts will be in vain.

Heat Loss through Van Windows

Radiant heat from inside your van escapes through windows, the heat loss through glass is not as bad as through metal, but it is certainly worth spending some time improving this area.

Just as we have talked about insulating the bodywork of a van, insulation can be added to windows in the form of thermal window covers. The benefits are the same as when insulating the bodywork.

The choice of material you use for van window coverings is worth careful consideration so that it’s possible to use them in both winter and summer.

Foil insulation products (usually supplied on a convenient roll) make ideal thermal window coverings, it is widely available and used in a multitude of applications in the building industry.

This stuff is simply bubble wrap with a layer of aluminium foil on either side. It's a great choice because it’s durable, easy to put up and has the rigidity to stay in place.

The layer of bubble wrap serves the purpose of adding thermal insulation to your windows, slowing heat transfer out of your van in winter (or into your van in summer).

The thicker the better but bear in mind you’ll need to store these when they're not in use, you don’t want to have to hitch a trailer just for your window blinds!

As a bonus the reflective foil surface reflects heat back inside during the winter and in the summer it does a great job in reflecting heat transferring infrared waves (from the sun) away from your van.

Hopefully this article has helped you take measures in reducing heat loss from your van in winter so you can remain warm and comfortable during the colder months.