Why Radiators Go Under Windows: Explained Simply

Why Radiators Are Installed Under Windows: Smart Design Backed by Physics

Why is the radiator under the window? It’s a layout we all know—radiators placed just below the window, whether in homes, offices, or apartments. But have you ever wondered why? Is it just an outdated design habit, or is there a logical, functional reason behind this widespread standard?

Let’s take a closer look at the practical and physical principles behind the radiator under window setup—and why it still makes perfect sense today.

Windows: The Weakest Point of Thermal Insulation

Even with modern triple-glazed windows, glass surfaces remain the coldest part of any room. Compared to walls, windows allow more cold to pass through.

This results in:

• A noticeable chill near windows
• A downward draft of cold air falling toward the floor
• Moisture condensation on the glass—especially with poor air circulation

That’s where the under window radiator plays a crucial role.

Reason 1: A Radiator Below the Window Balances Temperature Differences

A radiator placed beneath a window generates a rising stream of warm air, which:

• Neutralizes cold air descending from the window
• Enhances air circulation and distributes heat more evenly across the room
• Improves comfort—less perceived chill even at the same room temperature

This principle is known as a thermal curtain: the radiator acts as a barrier between the cold glass and the rest of the room, preventing cold drafts from spreading.

Reason 2: Efficient Use of Interior Space

The area under a window is usually dead space—it can’t be used for furniture because it blocks natural light and view. Placing a radiator below the window makes the most of this area.

Benefits include:

• Saves usable space in the room
• Doesn’t interfere with furniture placement
• Doesn’t disrupt the interior design

This is especially true for low radiators under windows, which are perfect for low window sills or rooms with floor-to-ceiling windows.

Reason 3: Supporting Natural Air Circulation

A radiator under the window supports the chimney effect—warm air rises while cool air sinks.

This setup enables:

• Natural air exchange in the room
• Even heating from floor to ceiling
• Faster response to sudden drops in temperature

Placing the radiator on a different wall would disrupt this flow—warm air would rise inefficiently, and the area by the window would remain uncomfortably cool.

Reason 4: Preventing Condensation and Mould

In combination with proper ventilation, a radiator under the window helps reduce humidity and prevents condensation from forming on the glass.

Without this thermal barrier, problems may include:

• Condensation on windows
• Mould growth around window frames
• Poor indoor air quality

This is particularly important in winter when the contrast between indoor and outdoor temperatures is at its peak.

Is Under-Window Placement Still Necessary Today?

In modern architecture—featuring large floor-to-ceiling windows, glass walls, or passive houses—the traditional radiator placement isn't always ideal.

In these cases, consider:

• Low-height panel radiators (e.g. RADIK KLASIK, height 200 mm)
• Hot-water convectors (especially floor models)
• Design radiators placed strategically in the room

Still, in homes with a standard sill and window, the radiator under window remains the most effective and practical solution.

Pro Tip: Don’t Underestimate the Type of Radiator

When choosing the right under window radiator, keep in mind:

• Window sill height – opt for a low radiator
• Room size – ensure adequate heating output (consult heat loss calculation)
• Connection method – side or centre connection
• Design – smooth front panel (e.g. RADIK PLAN) or fan-assisted (e.g. RADIK V-POWER) for low-temperature systems

Summary: Why Install a Radiator Under the Window?

KORADO’s Recommendation

Whether you’re renovating or building a new home, placing the radiator under the window remains the smartest choice from both a physical and comfort standpoint.

Looking for a stylish, efficient, and quiet radiator for your modern home?
Explore the RADIK panel radiator range from KORADO—from traditional designs to high-performance models with built-in fans for low-temperature systems.