Thermal performance of aluminium front doors: what to look for

An aluminium front door performs well thermally when it combines four things: thermally broken profiles, a panel with an insulating core covering the door leaf, continuous seals around the whole perimeter and an installation that is properly sealed into the opening. The figure that sums up the result is the Ud value of the complete door, in W/m²K, and you should always ask for it for the actual configuration you are buying.

This article explains what each element does and how to compare quotes.

Why does aluminium need a thermal break?

Aluminium is an excellent conductor of heat. A solid profile running from outside to inside acts as a bridge for heat to escape, and in winter the inner face gets cold and can even attract condensation.

A thermal break solves this by splitting the profile into two parts joined by strips of insulating material, usually polyamide strips. Heat no longer has a continuous metal path to follow. For residential entrance doors, this is now the starting point for any solution where thermal performance matters.

What part does the panel play?

On a front door, most of the area is panel, so the panel has a big influence on the final performance.

Insulating core

An aluminium door panel is usually a sandwich: two aluminium skins with an insulating core in between. The thickness and type of core affect insulation, stiffness and weight.

A panel that covers the leaf

On a monobloc door, the panel is bonded over the leaf on both faces so the frame profile is hidden, giving a flush look. As well as the visual effect, this increases the overall thickness and reduces the area of exposed metal, which tends to help thermal performance.

Glazing in the panel

If the door is glazed, the type of glass matters. Low-emissivity double or triple glazing with warm edge spacers reduces heat loss. A large area of poorer glass drags down the whole door.

Seals and threshold

A lot of the comfort at an entrance is lost through air leakage, not only through conduction through the materials. Look for:

• seals around the whole perimeter of the leaf, on more than one plane;
• a threshold that seals well without creating an unnecessary step;
• a multi-point lock, which pulls the leaf against the seals at several points along its height.

On pivot doors, sealing on the pivot side deserves particular attention, because there is no continuous rebate.

Installation: where performance is won or lost

A door with a good Ud value that is badly installed will not deliver what it promises. On site, check that:

• the gap between the frame and the wall is filled with insulating material and sealed against air and water;
• the door lines up with the insulation layer in the wall, wherever the design allows;
• the threshold is tied into the waterproofing of the external floor.

This part is the responsibility of the fabricator or installer, and it is a good reason to choose someone who knows the system well.

Why is my hallway cold next to the front door?

If you already have an aluminium door and feel the cold in the hall, the usual causes are these, in order of frequency:

1. Air getting through at the threshold or the side seals, because they are worn or because the leaf has dropped and no longer presses against them.
2. A badly sealed gap between the frame and the wall.
3. Profiles without a thermal break, common on older doors, which get cold on the inside and can attract condensation.
4. Single glazing or poor glass over a large area of the leaf.

The first two can often be fixed with adjustment, new seals and fresh sealing. The last two can only really be solved with a new leaf or a new door.

How to read and compare Ud values

What it is

Ud is the thermal transmittance of the complete door: frame, leaf, panel and glazing. It is measured in W/m²K. The lower the figure, the better the door insulates.

How it is obtained

In Europe, external pedestrian doors are covered by the product standard EN 14351-1, published in the UK as BS EN 14351-1. The thermal value is calculated or tested to specific European standards, either for a reference size or for the actual size of the door.

Points to watch when comparing

• Check that the values refer to the same door size.
• Check whether the value is for the panel, the profile or the complete door. Only the complete door figure is useful for comparing doors.
• Ask for the exact configuration: panel thickness, core, glazing, threshold.

What do the regulations require?

Thermal requirements depend on the country, the type of work and the climate zone:

• United Kingdom: in England, Approved Document L sets a maximum of 1.4 W/m²K for replacement external doors in existing dwellings. Scotland, Wales and Northern Ireland have their own building regulations, so check the requirement that applies where the house is.
• Portugal: the energy performance of homes is governed by the framework of the national building energy certification system, and the entrance door contributes to the performance of the building envelope.
• Spain: the Código Técnico de la Edificación, in its basic document on energy, sets limits for the envelope that vary by climate zone. In Galicia, the colder zones need more attention.

The designer or the responsible professional should confirm the requirement that applies to each project.

Checklist when asking for a quote

• Thermally broken profiles.
• Panel with an insulating core and stated thickness.
• Type of glazing, if any.
• Seals and threshold described.
• Multi-point lock.
• Ud value for the complete door, for the stated actual or reference size.

How we can help

Portancora manufactures bespoke aluminium entrance doors, monobloc and pivot, and flush, grooved, glazed and stainless steel door panels, for homeowners, architects and fabricators. If you are comparing options for a project, send us the sizes and the type of door you are after and we can talk through the configuration. To choose the look of the door, you can start with the visualiser.