With the onset of cold weather, when there is an excessive amount of moisture in the air, and significant temperature differences, one of the most common problems drivers have is fogging of the windows in the car.
This phenomenon occurs when the ambient temperature decreases, causing the glass to cool. Accordingly, since it is warm in the cabin and moisture does not evaporate but cools near the glass, it settles on it in the form of tiny droplets. You only need to sit in the car for 2-3 minutes for the windows to be covered with the tiniest drops.
How fogging appears
Of course, in this case, visibility deteriorates dramatically, and the glass changes from transparent to frosted and murky. The driver ceases to see the surrounding environment, and he is also distracted when wiping the window on the go, thereby increasing the risk of accidents. If the blower and heating could somehow save the windscreen and the two front side windows, the rear ones simply “die.”
Why do windows fog up?
Condensation on the glass’s inner surface appears at even a slight temperature difference on one side and the other side of the surface. Even by one or two degrees Celsius. And the greater this difference — the faster and in greater volume the condensate appears.
So, it can appear not only in the most common case, when the driver or passengers get in a cold cabin, and due to their breathing, the mentioned condensate appears on the windows. This phenomenon can also occur in the case of, for example when driving through cold tunnels or under overpasses, that is, where the ambient air temperature is lower.
The physics here is simple. At an air temperature of +20°C and relative humidity of 60%, the amount of moisture is 9.6 g/m3. However, if the temperature is lowered to +9°C with the same humidity concentration, the relative humidity increases to 100%. And this is the direct cause of the appearance of condensation on the surface of the windows in the car.
In some modern cars, manufacturers use a hardware solution to prevent the windows from fogging up. This includes the use of an emergency window air blower or a climate control system. However, within the scope of this material, we will not consider this issue.
Causes of fogging
There are several main reasons why windows fog up. Moreover, each factor can affect both the overall situation of fogging and the ones where the windshield, only the side or rear windows will fog up more.
Clogged or too dense cabin filter
Because the cabin filter does not cope with its functions, a closed air space without ventilation is created in the cabin. The temperature rises over time, the air heats up, and the windows in the car fog up from the inside, according to the physical phenomenon described above.
Here it is worth noting that the cabin filter may not only be clogged but also simply incorrectly selected, in particular, too dense. Its material does not cope with sufficient air passage, and moisture remains in the cabin. For the same reason, the windows in the car fog up when the heater is turned on. In this regard, many motorists advise installing a standard filter during the cold season and a charcoal filter during the warm season. The standard one is not as dense, and accordingly, passes air through itself better.
Wet seats in the passenger compartment
The main reason the seats become wet is that a certain amount of moisture enters the interior and is absorbed by the foam seat. In turn, this phenomenon can be caused by the following factors:
- the presence of passengers or the driver in the cabin in wet outerwear (after snow, rain);
- bad (old, rotten) rubber seals on the vehicle windows or doors;
- prolonged presence of the car with the doors open in a humid area;
- getting liquid on the seats (a banal spill of water or other liquid, because of which it is absorbed and can stay inside the seat for a long time).
It is also worth noting that the humidity in the cabin can also increase because the car has been standing in the cold for a long time and then abruptly moves into a warm atmosphere.
Moisture under the mats
Wet floor mats are also the main source of moisture in the car interior in winter and autumn. And in turn, they are the cause of significant fogging of the windows. There are several reasons why moisture accumulates on or under them:
- clogged drainage holes in the floor;
- brought and subsequently melted snow in winter or wet shoes of passengers/drivers in the rain;
- a leaking (even slightly) heater or its mains.
Incorrect windscreen air flow
Usually, this phenomenon occurs due to problems with internal ventilation. The windows do not fog when the ventilation of the air masses is properly turned on. The exception is the rear window at -15°C. As a rule, clogged ventilation ducts or a recirculation valve are to blame. In addition, if the car is old, the ventilation pipes may be simply leaky, and holes have formed in them. Also, remember that to blow the windows from fogging, you need to take the air from the outside, that is, turn off the internal air recirculation.
At the beginning of the movement, the entire air flow is first directed to the windshield, then to the front side windows, and then to the rear windows. The mode of ventilation and heating is regulated not in the service station but while driving, depending on the state of the interior and external factors that change every few minutes. First, you need to get your hands on your car’s manual and read the section “Heating and ventilation.”
Quite often it happens that the driver does not even suspect that the recirculation valve is broken, but continues to drive, and wonders why the air in the cabin becomes too heavy too quickly, or there is a smell of dampness (in such a situation, it helps either to fix the breakdown, or temporarily remove the cabin filter, if of course it has recently been changed, and the smell is still there).
The fumes of passengers are a common reason for car windows fogging up. This is an interesting physical phenomenon. Why windows fog up is based on the fact that ethyl alcohol can heat up and attract water vapor. Because of this, we get a situation when the moisture available in the interior air becomes more concentrated, and in this form even more densely settles on the inner surface of the car windows.
In this case, we mean a leak or complete failure of the heater. In the first case, the moisture from it can get on the mat, forming additional moisture in the cabin.
In the second case, a complete breakdown leads to the fact that the air and fluid are not being heated, so there will be no dehumidification of the air in the cabin, and therefore the fogging will continue.
What to do if the windows are fogging up
There are 10 useful recommendations that will help you deal with the situation when the windows in the car are fogging. These include:
- The windows inside the car must always be clean. You cannot touch them with your hands. You must wash them with detergents and then wipe them dry with clean material. It is useful to treat the windows from freezing at temperatures below 25 degrees below zero and when traveling with passengers.
- Use an anti-fogging agent to prevent the windows in the car from fogging up. This treatment will allow in humid and winter time to significantly reduce or completely remove (depending on humidity and temperature) the fog on the glass’s inner surface.
- It is necessary to monitor the condition of the cabin filter and the heater. Their proper functioning will allow you to quickly get rid of fogging when the car engine is running.
- Follow the warm-up sequence. Direct the warm air to the windscreen first, then to the side windows, and only then to the rear window.
- Adjust the correct air intake. It should come from the outside because it is the outside air that is not as humid as inside the cabin.
- Monitor the condition of the interior ventilation. If necessary, check and clean the drainage channels.
- Turn on not only the heater but also the air conditioner (if any). It is necessary to use a car air conditioner both in heat and in the cold. With it, you can quickly get rid of fogging by turning it on to the warm mode (provided that the air conditioning system is working properly). It dries the air well. We have a guide on choosing the best Car AC Recharge Kits.
- Dry the interior. Rarely do the windows fog up when the car is stored in a warm garage. When drying, it is advisable to open all the doors in a warm and dry room.
- The climate control system must be deactivated.
- Check the air recirculation valve.
It is advisable to periodically, at least during the change of seasons, check and change the air filters (in particular, the cabin filter, if available), clean the ventilation channels, clearing them of small debris and dust, check the air recirculation valve (if available), through which the filtered outside air enters the cabin.
It will also help to get rid of the problem of foggy windows in the car by periodically checking the leaky places of the vehicle, such as antenna sockets and window seals, to prevent precipitation from entering the cabin.
Advancing in solving the problem, motorists use many different clever ways and methods to eliminate fogging of the windows. It all starts with slightly opening the window so that fresh air can enter the cabin. The problem is solved by itself — someone uses various sprays, “anti-foggers,” a wide selection of which is offered on the market. But all these methods are for the most extreme case or as a temporary solution to the problem.
The above procedures will allow you to partially or completely get rid of the situation when the windows in the car are fogging up. This depends on the set of measures taken and the specific situation (the level of humidity in the cabin, the serviceability of ventilation, the heater, and other listed hardware).