Window energy calculator — assess energy efficiency and compare companies
The window energy calculator on OKNA.ua helps you assess a window's energy efficiency and approximate heat loss depending on its configuration: the glazing unit type, the presence of i-glass and argon, the profile chamber count and the size. The main indicator of a window's warmth is the heat-transfer coefficient Uw: the lower it is, the less heat the window loses in winter. Assess the options online and compare offers from many companies independently to choose a warm window. OKNA.ua is a niche platform about windows and doors specifically, running for more than 25 years (since 1999): here you compare offers from many verified companies in one place.
How to use the window energy calculator
To assess energy efficiency, set the window parameters in the calculator:
- The glazing unit type — single-, double- or triple-chamber (2, 3 or 4 panes).
- Energy-saving glass — the presence of i-glass (Low-E) and argon fill in the chambers.
- The profile — chamber count and frame depth.
- The window size and number of sashes.
The calculator shows an approximate assessment of energy efficiency and heat loss for the chosen configuration. This is a preliminary estimate for comparing options — the exact Uw and Ug values for your window are confirmed by the chosen company.
What an energy-efficient window is
An energy-efficient (energy-saving) window is a window with a low heat-transfer coefficient that lets less heat out in winter. A window's warmth is described by the heat-transfer coefficient, denoted by the letter U and measured in W/(m²·K):
- Uw (window) — the heat-transfer coefficient of the whole window: frame, glazing unit and spacer together. It is Uw that characterises the finished window.
- Ug (glass) — the heat-transfer coefficient of the glazing unit only (the glass part).
The lower the coefficient, the warmer the window and the smaller the heat loss. In Ukraine, windows are manufactured to DSTU EN 14351-1:2020 "Windows and doors. Requirements. Part 1. Windows and external doors", under which a window's heat-transfer coefficient Uw is determined and declared. The exact Uw value for your configuration is stated by the chosen company. To guard against summer overheating in sunny flats, multifunctional glass is added.
Uw and Ug — the difference
Ug is an indicator of the glazing unit only, while Uw is of the whole window together with the frame and the way the glazing is fitted. Uw also accounts for the frame and the edges of the glazing unit, so it usually differs from Ug. When choosing a window, go by Uw — it shows the real warmth of the whole structure, not of a single pane.
What a window's energy efficiency depends on
- Glazing unit — the main factor: chamber count (single-/double-/triple-chamber), the presence of i-glass (Low-E) and argon fill. Glazing units are made to DSTU B V.2.7-107:2008 "Sealed glass units for construction".
- i-glass (Low-E) — a low-emissivity coating reflects heat radiation back into the room and reduces heat loss in winter.
- Argon — an inert gas instead of air in the glazing chambers; it has lower thermal conductivity than air, so it reduces heat loss.
- Profile — more chambers and a greater frame depth retain the frame's heat better.
- Warm-edge spacer — reduces heat loss and the risk of condensation along the edge of the glazing unit.
- Installation — a quality, airtight joint keeps out cold and moisture where the window meets the wall.
How to reduce heat loss through windows
To make a window lose less heat, pay attention to the specification:
- Choose a double-chamber glazing unit (three panes) for homes in most regions.
- Add energy-saving i-glass (Low-E) — a single-chamber unit with i-glass approaches a standard double-chamber unit for warmth.
- Order argon fill in the chambers.
- Take a profile with more chambers and greater frame depth.
- Choose a warm-edge spacer.
- Order quality installation with an airtight joint — even a warm window loses heat with poor fitting.
The chosen company will match the optimal specification to your home, region and floor.
Why people choose energy-efficient windows on OKNA.ua
- Narrow specialisation for 25+ years. OKNA.ua is a platform about windows and doors specifically, running since 1999 — not a general marketplace.
- Comparing offers from many companies independently. You compare glazing units, profiles, warmth figures and prices from many companies in one place — independently, not from a single seller.
- Verified manufacturers and sellers. The platform lists companies that make windows to your dimensions with the declared characteristics.
- Transparent prices and warranty. You see "from" prices across companies and choose by cost and lead time; the warranty is provided by the chosen company.
How to choose a warm window and order it
- Assess the options' energy efficiency in this calculator and estimate the cost in the window calculator.
- Choose a company in the catalogue — by price, rating and lead time — and send it a request.
- The chosen company will measure, confirm the Uw and specification, manufacture and install the window with a warranty.
For details on glazing units — glass types, chambers, argon — see the glass units or PVC windows section.
Questions and answers
What is an energy-efficient window?
It is a window with a low heat-transfer coefficient Uw that loses less heat in winter. Energy efficiency is provided by an energy-saving glazing unit (i-glass, argon), a multi-chamber profile and quality installation. To guard against summer overheating in sunny flats, multifunctional glass is added. The lower the Uw, the warmer the window and the smaller the heat loss.
What are Uw and Ug?
Uw is the heat-transfer coefficient of the whole window (frame, glazing unit and spacer together), Ug is the heat-transfer coefficient of the glazing unit only. Both are measured in W/(m²·K); the lower the value, the warmer. When choosing a window, go by Uw, because it characterises the whole structure, not a single pane.
How do i-glass and argon affect warmth?
i-glass (Low-E) has a low-emissivity coating that reflects heat radiation back into the room and reduces heat loss in winter. Argon is an inert gas used to fill the glazing chambers instead of air; it has lower thermal conductivity, so it further reduces heat loss. Together they make the glazing unit warmer without changing its appearance.
How many chambers are needed for warmth?
For homes in most regions, people take a profile with 5–7 chambers and a double-chamber glazing unit (three panes) with i-glass and argon. A single-chamber unit suits balconies and warm regions; a triple-chamber one is for cold regions and noisy streets. The chosen company will advise the optimal number of profile and glazing chambers for your home.
How do I reduce heat loss through windows?
Choose a double-chamber glazing unit with energy-saving i-glass (Low-E) and argon fill, a profile with more chambers and greater frame depth, a warm-edge spacer and quality installation with an airtight joint. Even a warm window loses heat with poor fitting, so installation matters as much as the glazing unit.
Do energy-saving windows save on heating?
Energy-efficient windows reduce heat loss through the window (a lower Uw), so they help retain heat in winter. How much this affects heating bills depends on many factors — the glazed area, wall insulation, the type of heating and the climate — so there is no single percentage of savings. Assess the options in the calculator and compare companies' offers on OKNA.ua.
To what standard is a window's Uw determined?
A window's heat-transfer coefficient Uw is determined and declared to DSTU EN 14351-1:2020 "Windows and doors. Requirements. Part 1. Windows and external doors", and glazing units are made to DSTU B V.2.7-107:2008 "Sealed glass units for construction". The verified companies in the OKNA.ua catalogue work with glazing units and profiles that carry declared warmth figures.
