Select the structure and the required work. We will calculate the price based on the information provided. Below, you can easily check a window or exterior door according to the applicable Lithuanian STR: the city and wind region, opening rules, thermal properties, air, water and wind classes, usage cycles, marking and documents. Practical recommendations for the profile, glazing unit, hardware, seals and maintenance are clearly separated from the mandatory STR requirements. You will also find an interactive six-condition window heat-zone map and 8-question diagnostics, “Window or room?”, as well as interactive tools on ventilation, radiators and condensation.
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Answer a few simple questions. You will see what is worth checking, what can be repaired and when it is better to consider replacement.
Lifting the handle operates additional locking points only in the mechanism designed for this purpose. Tightness is assessed by checking all zones.
For a new product: request the Uw of the entire window / Ud of the door, declared performance characteristics, and appropriate wind, water and air classes.
According to the selected location — indicative STR table value. уточняется during design.
For a new product: request the Uw of the entire window / Ud of the door, declared properties, and appropriate wind, water and air classes.
The new STR 2.02.12:2026 will enter into force on 2027-01-01; its rules do not apply today.
Select a city: outdoor temperature and humidity will be obtained automatically. Compare ventilation time, window opening and heat losses.
Fetching current weather data…
Open-Meteo ↗Outdoor data from Open-Meteo, updated every 15 min. Outdoor humidity is shown for informational purposes: temperature is used in the heat loss formula. Measure indoor humidity with a hygrometer.
A heat recovery ventilator returns part of the heat from the extracted air to the supplied air. An air vent and an open window do not return heat.
An open window usually lets the most air through in a short time, but at the same time causes the greatest instantaneous heat loss and a draft.
Passive cold-air intake
Fast natural ventilation
Select the actual position — the air volume and heat losses will be recalculated automatically.
Balanced ventilation with heat recovery
Q = 0.335 × L × (Tin − Tout) × t / 1000QHRV = Q × (1 − η)Tsupply,HRV = Tout + η × (Tin − Tout)Airflows are indicative. The actual airflow through an open window or passive air vent depends on the window size, wind, pressure difference and operating extract ventilation.
Outdoor air enters without preheating and without heat recovery. The colder it is outside, the more heat the heating system has to supply.
A trickle vent can help reduce humidity and the risk of condensation, but it is not a heat recovery ventilator. In cold weather, it increases the heating load and may cause a draught sensation. For continuous winter ventilation with lower heat losses, a balanced ventilation system with heat recovery is more rational.
P = 0.335 × L × max(Tin − Tout, 0)E30 = P × h/day × 30 / 1000RHwarm = RHout × psat(Tout) / psat(Tin)The actual airflow through a passive trickle vent depends on wind, air pressure, the pressure difference and mechanical extraction. Therefore, the heat loss calculation is indicative.
A radiator under the window creates an upward flow of warm air. Blocking this flow can cool the inner pane, increasing the risk of condensation.
Important: condensation on the glass is mainly determined by indoor humidity, so “Humidity indoors” remains manually controlled here.
The number of panes alone is not enough: the Low-E coating, cavity, gas and spacer are important. If you do not know, select “old” for an old glazing unit.
If you do not know, select “Unknown”. An approximate range of possible edge temperatures is calculated, not the exact result for one window.
Warm air rises, warms the colder area by the window by moving air, and creates a warm-air “curtain” near the glass. This improves comfort and helps keep the inner glass warmer.
A wide windowsill, thick curtains or a screen do not always cause condensation. The risk also depends on humidity, outdoor temperature, the glazing unit and the actual air circulation.
Tcenter ≈ Tin − Ug × Rsi × (Tin − Tout) − ΔTobstacleA = Šilto oro apipūtimas / 100γ = ln(RH/100) + 17.62·T/(243.12+T)
Tdew = 243.12·γ/(17.62−γ)Ug — glass centre thermal transmittance coefficient, Rsi — internal surface thermal resistance. The edge range is calculated using illustrative fRsi limits. This is not a certified 2D thermal bridge calculation. Surface temperature measurement is required.
A short test shows whether a new seal can actually help, or whether the problem lies in the compression, window geometry, installation joint or the glazing unit itself.
These are OUTDOOR air data, not indoor humidity. They do not, by themselves, determine whether the seals need to be replaced.
Place a strip of paper between the sash and the frame, close the window and check in several places around the entire perimeter.
If the window is already airtight, a new seal hardly changes the thermal properties of the insulating glass unit. It does not change Ug and does not make cold glass into a “warmer insulating glass unit”.
Indoor temperature and humidity are not obtained from the internet. If you have a hygrometer, enter the actual values only. The dew point by itself does not determine the temperature of the edge of the glass.
The seal makes the air gap airtight. It does not change the Ug of the insulating glass unit. If the window is already airtight, a new “rubber seal” usually does not solve the problem of cold glass or condensation.
After sealing an leaky window, the draught may decrease, but without proper ventilation, indoor humidity may even increase. Therefore, condensation will not necessarily disappear on its own.
The test assesses three things: where air is getting in, how firmly the sash is pressed against the frame, and whether the seal itself is physically damaged. This is a diagnostic scheme, not a laboratory airtightness measurement.
Answer 6 questions: you will see why the window may fog up and what to check first.
Fetching outdoor data…
You can change the outdoor temperature manually. Set the indoor humidity according to the hygrometer.
Click a window zone — the symptom, causes and checking steps will change.
You can change the outdoor temperature manually. Set the indoor humidity according to a hygrometer. Measure indoor humidity with a hygrometer. Outdoor humidity is not room humidity.
A new seal or a triple-glazed unit does not eliminate every cause of fogging. First determine where the water appears and why the surface cools down.
Drying laundry indoors, cooking, bathing, many occupants, aquariums and plants increase humidity. Condensation forms on a cold surface.
Check both the air supply and the extraction. A working fan does not guarantee the required airflow. Possible solutions: adequate air supply, heat recovery ventilation, a dehumidifier.
Thermal bridges may occur due to insufficient insulation of the reveals, an improper joint beneath the windowsill or damp walls. The joint on the inside must be protected from humid air, and on the outside from rain, while being able to dry. Specific tape brands, 3 cm insulation and a 3-chamber subsill profile are not universal STR requirements.
Airflow (m³/h) = room volume (m³) × air changes per hour. The 8 air changes for a kitchen and 6 air changes for a bathroom given in the text are examples, not universal mandatory STR values.
Enter the room dimensions. You will get its volume and an approximate fan capacity.
Open the air supply vent or window, switch on the extraction and hold a sheet of paper against the grille: the sheet may show the direction of airflow, but it DOES NOT CONFIRM the amount in m³/h. Measuring the amount requires an anemometer and the grille's free area or a special airflow meter.
8 and 6 air changes per hour are example calculation options, not universal mandatory STR requirements. A kitchen cooker hood and continuous ventilation of residential premises are not the same thing.
The diagram shows only typical inspection zones, not a real thermogram. The glass temperature is an approximate model, not a measurement or expert assessment.
The dew point is calculated using the Magnus formula; the internal glass temperature is approximated as follows: Tst = Tlauko + f × (Tvidaus − Tlauko). f is an approximate coefficient corresponding to the selected type of glazing, reduced by limiting the warm airflow from the radiator. The actual temperature depends on the glazing unit composition, glass edges, wind and installation.
8 simple questions. Find out where to look for the problem first: in the window, room humidity and ventilation, or the installation joint.
Getting weather data…
Outdoor relative humidity is not indoor humidity. Indoor humidity cannot be determined online.
This is an indicative assessment of symptoms, not an inspection or official expert assessment. Several causes may act at the same time.
Excessive compression squeezes the seal, makes the handle harder to operate, and increases the load on the drive mechanism. We adjust it only after assessing the sash geometry and the position of the locking points.
Moisture on the room side is usually related to surface temperature and air circulation. Moisture between the panes indicates lost insulating glass unit tightness. Outdoor condensation may be a sign of a high-performance thermal glazing unit.
Briefly describe the fault, specify the city and, if possible, send a general photo of the structure and hardware. Call+370 612 45 700.
We come to Klaipėda and the surrounding cities and settlements: Palanga, Šventoji, Gargždai, Kretinga, Šilutė, Slengiai, Ginduliai, Vėžaičiai, Dovilai, Priekulė and Dreverna. We arrange the arrival time in advance.