In the threshold area of the entrance door, as a rule, there is a bridge of cold. The threshold can not be a height of 60-70 mm, as, for example, the lower part of the window, because it is necessary to provide accessibility (for people with special needs, the elderly, children, etc.). The maximum height of the protruding part of the threshold above the floor level is 25 mm (to provide access in public places).
The threshold for entrance metal-plastic doors is traditionally made of extruded aluminum. It is strong enough, but it creates a bridge of cold. The necessary reduction in the height of the thresholds creates structural difficulties with sealing loops. Leakage and cold construction of the thresholds lead to condensation and even icing of the entrance door at the bottom, as well as to large heat losses due to incoming cold air through the slots. As a result, the front door becomes a "weak link in the insulation" in the external contour of private houses, the outer doors of apartment buildings, public and commercial buildings.
Another irony is that the building is checked for air permeability using the Blower Door test - a mandatory test in determining the energy efficiency class of the house. When testing a building in the opening of the entrance door, an airtight partition with a fan is installed. As a result, this test does not take into account one of the biggest problems in sealing the house - sealing the front door in the threshold area.
Thus, even if the house receives a high energy efficiency class and must save a lot of money on heating and air conditioning, in practice everything may not be so optimistic. Wreck through a non-insulated part of the front door "blow out" all the savings from investments in energy efficiency of the building.
A draft in the door entry threshold is a common problem for steel, wooden and metal-plastic doors.
One such gap can negate all the costs of replacing windows and wall warming
Video: Sveta Malinina, YouTube
On the one hand, the threshold should be strong, because it is attacked, and flat, so as not to stumble over it. This is completely different from, for example, the lower part of the window: the projection of the frame does not bother anyone, it reliably and tightly closes with the sash, blocking it.
Normally the thresholds were made from aluminum, and the lower they are, the less reliable the seals are. As a result, the thermal insulation
The solution to this problem can be, for example, the use of a special warm threshold, which consists of a combination of aluminum and plastic. This threshold allows almost completely breaking the cold bridge in the lower part of the door.
Buy a warm threshold and replace it yourself, without dismantling the door, it is impossible. Therefore, when buying a metal-plastic front door, require a warm door threshold. This is a question of the energy efficiency of the whole house.
Another "weak" place - it's the corners of the door of the lower part, along which there is a draft. To isolate these places, so-called windstops are used that cover such slots.