How to choose an insulated glass unit: chambers, spacers, glass

Glass makes up most of a window’s area, so the insulated glass unit largely determines its thermal and acoustic performance, and knowing how to choose an insulated glass unit matters as much as choosing the profile. The short answer: for homes in Baku a double-chamber unit such as 4-10-4-10-4 is the usual choice, a single-chamber 4-16-4 is typically enough for balconies, the solar-control pane goes on the outside, and a tempered pane is added wherever safety matters. Below are the questions we discuss with customers at the Magna factory every day.

One chamber or two: which unit do you need?

A single-chamber unit (e.g. 4-16-4) has two panes and one air cavity. It is sufficient for balconies, unheated spaces and budget projects.

A double-chamber unit (e.g. 4-10-4-10-4) has three panes and two cavities. In Baku’s climate it is the standard choice for residential buildings: heat loss in winter, cooling load in summer and street noise all drop noticeably. It is heavier — the profile and hardware must allow for that. Both options, plus non-standard configurations, are described on our insulated glass units page.

Criterion	Single chamber, 4-16-4	Double chamber, 4-10-4-10-4
Panes / cavities	2 / 1	3 / 2
Overall thickness	24 mm	32 mm
Glass weight with 4 mm panes	about 20 kg/m²	about 30 kg/m²
Thermal insulation	Good	Noticeably better
Noise reduction	Basic	Better
Typical use	Balconies, unheated rooms, interior screens	Living rooms, bedrooms, offices

What spacer width should you choose?

The spacer is the aluminium frame that keeps the panes apart. Magna stocks 6, 8, 9, 10, 12, 14, 16, 18 and 20 mm spacers; in our IGU assembly service the spacer is filled with desiccant and the unit is sealed with a primary and a secondary seal.

Spacer	Typical use
6–9 mm	Slim profiles, interior partitions
10–12 mm	Each cavity of a double-chamber unit
14–16 mm	Optimal insulation for a single-chamber unit
18–20 mm	Large panes, special projects

Rule of thumb: in a single-chamber unit every extra millimetre up to 16 mm improves insulation; beyond 18 mm convection starts inside the cavity and the benefit fades.

Heat or noise: what matters more for your windows?

No single unit solves every problem equally well, so decide on the main concern for each elevation.

• Winter heat loss is reduced mainly by the number of chambers and the cavity width. Thicker glass adds very little here.
• Summer heat on south- and west-facing windows is best handled by a solar-control outer pane rather than by extra chambers.
• Street noise responds to mass and asymmetry: panes of different thickness, such as 6 and 4 mm, resonate at different frequencies and damp each other.

Main goal	What helps most	Example build
Lower heating bills	Second chamber, correct spacer width	4-10-4-10-4
Less solar heat and glare	Tinted or reflective outer pane	4 bronze-16-4
Quieter rooms on a busy road	Asymmetric panes, heavier outer pane	6-16-4
Safety at floor level	Tempered pane	4T-16-4
Large or exposed panes	Thicker outer pane	6-16-4 or 6-10-4-10-4

These are typical starting points, and goals can be combined — for example, a tempered tinted outer pane in a double-chamber unit. Noise also leaks through the frame, seals and installation joints, so a good unit cannot fix a poorly fitted window. We explain the effect of pane thickness on noise and wind load in our guide to choosing window glass thickness.

Which pane goes where?

• Outer pane — tinted glass or reflective glass: solar heat stays outside. Which of the two suits your façade is covered in our comparison of tinted and reflective glass.
• Inner pane — clear glass: natural light and true colours indoors.
• Tempered pane — floor-to-ceiling windows, doors, children’s rooms, public buildings. If the unit includes tempered glass, give exact sizes up front: a pane cannot be cut after tempering.

How thick should the panes be?

For a standard residential window a 4 mm pane is enough. If the pane is wider than 1.2 m or larger than 1.5 m², use 5–6 mm for the outer pane because of wind load and weight. We assemble units from 4, 5 and 6 mm panes. We cover this in more detail in our guide to choosing window glass thickness.

Do you need muntins (Georgian bars)?

In a muntin unit the decorative bars sit inside the cavity, so they do not get in the way of cleaning and do not fade. Points to check:

• the bars need room inside the cavity, so very narrow spacers may not be suitable — tell us the planned build and we will check it;
• the pattern follows your drawing, so give the bar positions in millimetres or as equal divisions;
• muntin units, like tempered ones, usually take a little longer to make than standard units.

How do you order without mistakes?

Common mistakes

Writing the formula itself is covered in our guide on how to read an insulated glass unit formula. Beyond the formula, we most often see:

• Sending the frame opening instead of the glass size. The unit is smaller by the clearances your profile system specifies.
• Measuring one window and ordering it for all. Identical-looking openings often differ by a few millimetres.
• Ignoring weight. A double-chamber unit on a large opening sash can exceed what the hinges are rated for.
• Deciding on tempering after delivery. A pane cannot be tempered or trimmed later, so mark the tempered panes in the order.
• Leaving out colours. Write “bronze”, “green” or “blue” for every tinted or reflective pane, not just “tinted”.

What to include in the order

1. Width × height (mm) and quantity for every item.
2. The unit formula, e.g. 4-16-4 or 4-10-4-10-4.
3. Pane types: clear / frosted / tinted (colour) / reflective (colour) / tempered.
4. A drawing if muntins (decorative bars) are required.

With this information Magna’s calculation software builds the cutting plan, works out spacer, sealant and desiccant consumption automatically and sends the quote within one business day. Send us your sizes and request a quote for your insulated glass units.