Warm Frame – what is it and what is it used for?

Are you facing a problem related to selection of windows for your house or flat? A seller has offered you windows with a warm frame and you wonder what this term means? What is a warm frame and is it worth to be applied? If you still hesitate to purchase a window with a warm frame, this section is for you.

Each new window is equipped with so-called distance frame, which separates the panes as part of double- and triple-pane packages. This inconspicuous and small element performs extremely important functions - it affects the heat penetration and is responsible for sealing the edges of double-glazed units.

Construction of double-glazed units to help you understand what a frame is all about.

A glazing unit consists of two or more glass panes separated by distance frames. The space between the panes is filled with air as a standard, whereas it is also practised to fill it with argon (Ar) or Krypton (Kr) noble gas to improve thermal transmittance parameters of the pane. To protect the space between the panes from moisture, the spacer is filled with a strong granulated hygroscopic agent. That is why the spacers significantly affect the thermal insulation of glass packages. There are, however, different types of distance frames.

Aluminium distance frames

The basic solution includes installation of a standard frame made of aluminium, which may be advantageous in terms of low price, but has the main disadvantage which is high heat transfer. This means that the frame becomes a weak part of the window and affects deterioration of insulation properties. The heat escapes from the house thus heating costs increase. Could this be avoided? Certainly yes, as so-called warm frames were designed to prevent this from happening.

Warm distance frames

As a result of growing popularity and demand for window constructions that limit the loss of heat energy and reduce "escaping" heat through windows, it has become necessary to develop a technology for the production of insulating glass units equipped with frames made of materials with lower thermal conductivity than aluminium. And so the era of warm frames was born.

A warm frame is called a distance frame made of materials with very good insulation properties - plastics or stainless steel.

What is a warm frame according to ISO standard?

Warm frame criterion according to PN-EN ISO 10077-1

In accordance with  PN-EN ISO 10077-1 standard, an edge with improved thermal parameters may be considered to state the following inequality:

Σ (diλi) ≤ 0,007 W/K

where:
di – material wall thickness
λi – material's heat conduction coefficient in W/Mk

On the basis of ISO standard, it can therefore be concluded that warm frames do NOT include those popular aluminium distance frames or steel frames. Frames made of stainless steel or plastic can be referred to as warm frames.

How does a warm frame affect window parameters?

The table below presents thermal results of various window structures. The table shows an influence of a distance frame on such parameters as:

Uw – heat transfer coefficient through the window
Psi - linear edge-to-edge heat transfer coefficient

The lower the values of these parameters, the better thermal insulation properties of the window.

The results of the tests show that use of a warm frame improves energy efficiency of the window even by Uw=0.1, which is a very high value that significantly affects comfort of living.

3 key benefits of selecting a warm frame

Firstly, lower heating costs

The first advantage of installing a warm frame is of course reduction of heat loss. Up to 20% of the heat can escape through an old-type leaking windows. Replacing the windows with those with a warm frame may bring considerable savings on long-term heating.

Secondly, this is a solution to the problem of moisture condensation on glass

Aluminium frames very often cause steam to accumulate around the frame in wintertime in poorly ventilated rooms. This is due to large temperature difference between external and internal panes. Application of a warm frame made of high-quality plastic allows to eliminate this problem. The purpose of a warm frame is to increase the surface temperature of the inner edge of the glass panes; this reduces the risk of condensation - especially in the corners.

Thirdly, increasing durability of windows

The purpose of distance frames is also to protect windows against ingress of dirt and moisture. For this purpose, a special gas - argon or krypton - is let in between the panes. A leaky frame causes the gas to escape and the glass package loses its properties. Additionally, a leaking frame causes moisture to enter the interior and mould to develop.

Testing the effectiveness of a warm frame

The German Institute of Window Technology in Rosenheim has been studying the impact of using various types of distance frames, including warm ones. The results of these studies showed significant differences. While keeping other parameters of a window the use of a warm frame reduced the total heat transfer coefficient Uw  by 7.7% up to 11% in comparison with use of woodwork including an aluminium frame. The lower Uw the lower the heat loss of the window joinery.

Should you be faced with a decision to choose a window joinery and you are still wondering what kind of distance frame to select, please contact us. Our experts will answer your questions.