It’s worth saying right away that one of the causes of condensation is incorrectly selected or installed windows. If you do not plan to change them, then possible solution to the problem could be an air dehumidifier, additional heating devices used in the area of window openings, as well as ventilation systems, including recuperators. But let's talk about everything in order.

What is window fogging?

To fully understand the process of fogging of window structures, one cannot do without the basics of physics. In this case, we are talking about condensation falling onto the surface of the glass (and not only). In turn, condensation is the transition of substance (in our case, water) from gaseous state to liquid one. Thus, the air always contains certain amount of moisture, and its consistency is determined by humidity indicators.

In this case, we usually operate with relative humidity indicators as percentage. It is reported in weather forecasts and demonstrated by devices such as humidifiers. But the conditional 50% is felt differently in winter and summer. For example, after summer rain in hot weather there is often feeling of steam room, and in cold season, it is worth opening the window (even if it is snowing) and the room almost immediately feels dry.

The thing is that there is also an absolute indicator of humidity, which reflects the real content of H2O in the air (measured in g/m³). And the higher the temperature, the higher the maximum moisture concentration can be. In other words, warm air contains more water, and cold air contains less. Accordingly, if the temperature is sharply lowered, condensation will begin - excess moisture will turn into liquid state.

Let's look at how this works with simple example. What happens if you take bottle of water out of the refrigerator in the summer? Water droplets will quickly appear on it. Why? The air circulating near the container is cooled. As temperatures drop, absolute humidity drops. The air can no longer hold all the moisture present in it. What happens to excess? It condenses, that is, falls on the walls of the bottle.

Condensation on bottle from the refrigerator and fogging of windows are the same physical process.

Similar processes occur, for example, with grass at night - it gets colder and excess moisture falls in the form of dew. Almost the same thing can happen with window structures.

Why are “crying” windows dangerous?

It’s definitely not worth putting up with the fact that condensation appears on glass or slopes. There are at least 3 risk factors caused by moisture on window structures:

  • the formation of mold and other fungi, which slowly but surely destroy repairs and are dangerous to human health;
  • dampness is desirable environment for the development of pathogens, both viral and bacterial in origin;
  • moisture does not directly harm glass and plastic profiles, but it negatively affects wooden frames and metal fittings, so condensation somehow reduces the durability of the window.
Leaving condensation and doing nothing is very bad decision.

If health, windows and repairs are important to you, then you need to understand the causes of fogging.

Why does condensation appear on windows?

If we speak immediately in essence, then there are two main reasons for the "fogging" of glasses:

  • heat loss in the window opening area;
  • increased relative humidity in the room.

For detailed explanation, one also cannot do without turning to physics. There is such term as dew point. This is the temperature at which moisture (that is, water vapor) begins to turn into liquid state, that is, to condense. Special dew point calculations have already been carried out and are in the reference tables, and the main variables are relative humidity and air temperature.

The settling point depends on the air temperature and relative humidity.

For example, if the room is 20 ° C, then at humidity of 40%, condensate will fall at an air temperature of 6 ° C. For example, when the operating mode in the refrigerator is set at 7 ° C, then condensate will not appear on the removed bottle, and if the device “cools” by 5 ° C, then the container will fog up. But already at humidity of 60%, the dew point is 2 times higher - 12 °C.

With warmer air in the room (and in winter it is often customary for us to heat up to +24 degrees), condensation temperatures rise. Accordingly, at 40% humidity the dew point is 9.5, and at 60% - 15.7 °C. It turns out that if the apartment is humid and warm in winter, then the probability of fogging windows is quite high. After all, glass is fairly cold surface due to its proximity to the street.

But let’s say our humidity is 50% and the temperature is 20 degrees Celsius. Could condensation then appear on the windows? The dew point under these conditions is 9.2 °C. If the window structures have warm double-glazed window, and the slopes are made with high quality (insulated), then the temperature on their internal surfaces should be clearly higher. But in practice, everything is not so if the windows were selected or installed with errors.

The factor of low thermal insulation of window structures is usually priority in case of fogging, especially in the presence of centralized heating. Radiators tend to dry out the air, relative humidity sometimes does not even reach 30%, and families try to raise these values to at least 45% by purchasing humidifiers. True, high humidity is also not uncommon, for example, with problematic (dilapidated) centralized ventilation, frequent cooking, an abundance of people, animals and domestic plants in the room.

In any case, first of all, you need to determine the exact cause of fogging in your situation. This can be done very easily, for example, using a hygrometer. If the humidity is not high, then the problem is clearly in the window. Without hygrometer, you can also check the window opening: any blowing or very cold inner surface of the glass is evidence of poor thermal insulation of the window structure.

How to increase the thermal insulation of window to prevent condensation?

There are several basic recommendations to improve the thermal insulation of the window opening:

  • Choose the right windows. For temperate climate (both continental and marine) in heated rooms, it is advisable to use windows with profile of at least 60 mm thick and double-glazed windows (that is, 3 glasses and two layers between them). This configuration provides sufficient thermal insulation, that is, the temperature on the inner surface of the glass will not differ critically from room temperature, that is, it will be above the dew point.
Good thermal insulation of windows is based on double-glazed windows.
  • Delegate window installation to professionals. Errors in the installation of the window structure can cause additional heat loss, for example, due to loose fit of the sashes or too large gaps between the frame and the wall.
  • Pay due attention to the finishing of both internal and external slopes. Typical mistake during repairs is the improvement of the window opening inside the room with complete lack of attention to the facade. If the gap is sealed from the outside only with mounting foam, then under the influence of moisture and temperature changes, its initial operational properties will deteriorate, it will begin to collapse, and the tightness of the gaps will disappear. As result, even in the presence of warm windows, the slope area can be serious source of heat loss, which often causes fogging in winter.
  • Do not interfere with the natural movement of air flow. Even if the tightness of closed window structure is not ideal, then heater can level out minor flaws. It is no coincidence that the radiators are located directly under the window. But natural circulation - with the movement of warm air upwards - can be disturbed either by thick curtains or very wide window sill. If the latter is design necessity or an additional piece of furniture (table or seat), then it is usually recommended to make several ventilation holes in the window sill to allow heat to move from the radiator to the top.
For normal air circulation, holes can be provided in wide window sill.
  • Do not forget about window maintenance, including the timely replacement of seals. This is consumable item that wears out over time, loses its original elasticity, and may begin to crumble. To extend the life of window seals, periodic lubrication and timely replacement with new ones are recommended. How can you tell if something is wrong with this accessory? Due to the fact that more effort is required to close and open the window, as well as blowing from the junction of the sash to the frame.

What to do if the window is already installed, but was previously selected incorrectly? Sometimes you can not change the design entirely, but replace only double-glazed window - put two-chamber instead of single-chamber. This procedure does not involve "dirty" work, but one cannot do without calling window specialists for measurements.

Also, almost at any time, you can redo the slopes and, for example, just close the mounting seam from the outside - using plastic, siding, foam, etc.

Another way to increase the thermal insulation of window opening can be to install an additional heater, for example, a ceramic convector. But this is fight against the effect, not an elimination of the cause.

Air handling units with heat recovery

How to reduce indoor air humidity so that there is no condensation on the windows?

If the house is hot and humid, then fogging can occur even with “warm” windows. For example, at temperature of 24 degrees Celsius and 70% humidity, the dew point is above 18 °C. In such situations, the main problem is the microclimate, not window structures. In addition, some window flaws can also be leveled by optimizing the temperature and humidity conditions in the room.

How can you effectively reduce the humidity in your home without additional investment? Here are some basic recommendations:

The simplest method of reducing humidity in winter is ventilation.
  • regularly ventilate the room;
  • use ultrasonic humidifiers wiselyby setting not too high values. Some performance models can increase humidity very quickly;
  • move indoor plants away from the window;
  • stop the practice of drying laundry near window opening.

In fact, even simple ventilation is enough to quickly reduce the humidity in winter. But this is not an ideal solution. And it's not that you can get sick because of drafts, which are so afraid of many mothers and grandparents. It is convenient to ventilate in small apartment, but in house with more than 10 windows, this is rather laborious process. Plus, by reducing humidity by opening the doors, we also noticeably cool the room. If centralized heating operates without heat metering devices, then there seem to be no special problems, but if you have an individual system, each ventilation is an additional cost for reheating the air.

What else can be done to improve air circulation? Think about proper ventilation even at the stage of buying window. This can be fittings for micro-ventilation (it is slot ventilation) or special ventilation valves (they are also called window ventilation). By the way, both of these options can be implemented after the installation of the window structure.

If micro-ventilation, that is, slight slot opening of the sash for air exchange, is quite familiar, then it is worth mentioning separately about the ventilation inlet valves. Such ventilation is mounted on the window (on the frame itself, on the sash, or between these structural elements - with part of the seal removed) or even in the installation seam. It should be placed closer to the ceiling, which eliminates discomfort for residents due to cold air masses. The valves ensure the flow of fresh air into the room by adjusting the dampers inside the structure. In addition to manual models, there are even fully automated solutions that can be activated, for example, by triggering humidity sensor. The damper opens little, and fresh air is supplied into the room from the street.

Another method to provide ventilation without opening windows is special supply valve.

In addition, it is worth checking and repairing the central ventilation duct. If, for example, it is clogged, then cleaning can come to the rescue. It is easy to check the operation of the hood using the old-fashioned method with lighter: if the flame next to the shaft does not even deflect, then there are definitely problems with the removal of air masses.

Otherwise, you can either specially dry the air or upgrade the ventilation system. There are no longer any costs involved. We will consider both of these options in little more detail.

Household dehumidifier is similar in appearance to an air purifier or humidifier.
Dehumidifiers

How to properly dry the air: the calculation of dehumidifiers

First of all, it is worth recalling that most modern split systems include dehumidification among their operating modes. Yes, their performance is not very high, but if you have an air conditioner, the first thing you should do is check this function in practice. Perhaps the appropriate mode in your case will help eliminate condensation on the windows, and additional costs will be avoided.

More serious units are full dehumidifiers for the home. Many manufacturers immediately indicate what area they are designed for. There are also special formulas that help you find the right device for your needs. Let us immediately make reservation that the most accurate figures will be provided by an expert assessment, which takes into account not only the area of the room, but also many other factors, including the size of the aquarium.

To roughly calculate suitable device, you can use the following formulas:

  • The optimal performance of dehumidifier (measured in l/day) can be determined by multiplying the area of the room by 0.7. That is, for room of 30 m², on average, models with an intensity of 21 l / day are enough. The full calculation includes determining the volume, multiplying it by absolute humidity in grams (it can be taken from reference books based on temperature and relative humidity). The resulting value is multiplied by 24 hours and divided by 1000. An approximate calculation usually gives an error of no more than liter.
  • The air flow of the dehumidifier should be at least two to three times greater than the volume of the room where it will be installed. Let's say there is room of 30 m² with ceilings of 2.8 meters, it contains total of 84 m³. Accordingly, the air flow rate of the dryer should be in the range from 168 to 252 m³/hour.

Both formulas are rough, but quite sufficient for everyday purposes. And if you focus on two parameters at once, and also take into account the recommended area of the room, then you are unlikely to go wrong with the final choice.

Which ventilation unit should I choose?

For forced ventilation today, various devices can be used, including:

  • exhaust fans and supply and exhaust devices. Both of them are usually installed in centralized ventilation duct and have low capacity. Supply and exhaust fans can be installed in window (which is why they are sometimes called window fans) or in wall opening, which makes them more versatile. But the choice of such devices today is small;
The simplest solution for ventilation is an exhaust fan in the bathroom.
  • so-called breathers, that is, supply ventilation units. They do not provide air exhaust, plus, as rule, they have additional heating devices so that cold air does not enter the room in winter. Such installations increase energy consumption;
  • recuperators. These are supply and exhaust devices with heat exchanger that allows you to equalize the temperature between incoming and outgoing air. Thus, in winter the new masses are no longer cold, and in summer they are not so hot. These are more energy efficient solutions with minimal power consumption.

Probably, the recuperator can be considered the best choice for ensuring comfortable microclimate, fresh air flow and removal of excess moisture. The performance of this installation can be calculated taking into account the area of the facility and/or the number of residents (people who are in the room).

Formula for determining productivity by area:

P = S x H x K, where

P—maximum air flow;
S is the area of the room;
H - ceiling height;
K is the correction factor for the type of room, for living rooms it is 1, for the kitchen it is 2, and for the bathroom it is 3.

For kitchen with an area of 20 meters and ceiling height of 2.8 m, you need recuperator with maximum air flow of at least the following value:

20 x 2.8 x 2 = 112 m³/h.

If we start only from the number of residents, then the maximum air flow is taken into account. According to building codes, balanced and increased optimal indicator is proposed for the microclimate per person - 25 or 36 m³/h, respectively. Let's say we have 4 residents, then our P value will be 100 and 144 m³/h, respectively. Ideally, the largest of all three obtained indicators (112, 100 and 144 m³/h) is what you should focus on when choosing recuperator.

The most energy-efficient ventilation in the apartment will be provided by recuperator.

For small apartments, they usually use one supply and ventilation unit with recovery, that is, it is necessary to lay down not the area of the kitchen, but the entire room and take the average correction factor (relatively the same “two”). And for large housing and houses, as rule, two devices are installed.

What is the best way to solve the problem of condensation on windows? Ideally, even at the renovation stage, it is necessary to provide for cool window designs (with high-quality finishing of the slopes), good ventilation, and popular climate control devices. If the problem of fogging is being solved at facility where repair work has already been done, then it is advisable to determine the exact cause (heat loss or high humidity) and eliminate it. When not everything is perfect with windows and ventilation, and the budget is limited, then you need to understand what is more profitable to implement. Sometimes it is cheaper to replace window structures than, for example, to buy and install high-quality heat exchanger.