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Carpenter Academy

Technical details for experts

Your guide to choose and correctly install the concealed hinge

Concealed hinges

In order to identify the correct hinge for your door installation there are various factors to take into account for its efficient functioning over time. The following will explain some key points to consider and cover the fundamentals.


The factors that influence the hinge choice and its position / installation

Door weight and dimensions

Door weight and dimensions

Hinge position and center-to-center distance

Hinge position and hinge spacing

Door usage

Door use



Mechanical stress that affects the installed hinges

Mechanical stress that affects the installed hinges


A - Door weight

B - Upper hinge pulling

C - Lower hinge pushing

Mechanical stress that affects the installed hinges

In other words the mechanical impact on the hinges is caused by:

1 - Door weight
2 - Door width
3 - Hinge to hinge distance (HINGE SPACING)


   The hinge undergoes a major influence by:
         1 - Increasing the door weight (A)
         2 - Increasing the door width (L)
         3 - Reducing the hinge spacing (I)

It is essential to define the number of hinges to install and their spacing for a correct application

 What is hinge spacing?

HINGE SPACING is the distance between the upper hinge and the lower hinge centre in the door (regardless of the use of any other hinges installed besides these ones)

Center-to-center distance examples

The hinge spacing affects the hinge capacity
  The smaller is the hinge spacing, the lower is the door capacity

The hinge capacity is inversely proportional to the door width
  The wider the door, the lower the hinge capacity 


By increasing the hinge spacing you can counterbalance the horizontal load of a door. (It is necessary to know the door weight and width)

Example with 2 hinges K1019 (40 kg)

The graph shows that 2 hinges have a capacity of 40 kg with a standard test door 900 mm wide with hinge spacing 1550 mm.
 By increasing the door width up to 1000 mm the hinge capacity gets reduced to 37 kg.

In order to get a 40 kg hinge capacity with a door width 1000 mm it is necessary to increase the hinge spacing to 1700 mm.

Example of a correct center-to-center distance between  2 hinges K1019

How to interpret the product profiles

Each hinge has a table in its profile with indications how to determine the correct hinge spacing.

How to determine the correct center-to-center distance

The technical details such as hinge spacing, capacity and door width applied in our labs to perform the tests determine the features.
Our tests are performed at IFT certified test-rigs and following EAD 020001-01-0405 test standards.

Installation examples


Standard position indications

Installation with 2 hinges


The central hinge maintains the
straightness of the door leaf, i.e. it
prevents it from bending in case of:

1 - Doors higher than 2100 mm
2 - Humid environment
3 - Light materials and/or thin doors
4 - Separated areas with different

Installation with 3 hinges


For higher / wider / heavier doors and/
or for high frequency use (eg public
places such as schools, hospitals,
airports, etc.)

Installation with 4 hinges

Examples of installation with accessories


For applications with a door closer and in case of the door widths over 900 mm, it is suggested to fit the third hinge in the upper part of the door (consult the capacity table for each model)

 The door closer adjustment must be as slight as possible but sufficient for its functioning.
The major force could affect the hinges.

Installation with an upper door closer

WITH A DOORSTOP (4 hinges)

For doors with a door closer or higher / wider / heavier doors and for high frequency use / (eg public places such as schools, hospitals, airports, etc.) and / or where accessories are installed such as doorstops, weatherstrips or gaskets and seals.

The doorstop is installed as far from the hinge axle as possible.
We suggest the distance of about 75% of the door width towards the lock.

Installation with a doorstop


The position of the 4 hinges with a door closer and weatherstrips or any other sealing accessory

Installation with a weatherstrip

Product profile




An accurate study of all the door installation details is essential for choosing the suitable hinge regarding its use

 It is essential to make an accurate installation and adjustment in compliance with the instructions by Krona Koblenz and considering the warnings provided with the hinge instructions are available from Krona Koblenz and downloaded from our website

- Place of installation (residential buildings, public places, offices, schools, airports, internal or external doors, etc.) and / or the frequency of use..

In frequently visited public buildings there is an intense usage due to the frequent opening and closing (schools, hospitals etc.). In this case suitable heavier-duty hinges (capacity) must be fitted, even if the door weight does not require them.
For external doors, corrosion resistance needs to be considered in choosing the correct hinge material or surface treatment.

Installation site

- Door weight.

You also need to consider the weight of the hardware and of any possible decoration.
The weight means the door leaf itself, without any fenestration or additional glass which can offset the centre of gravity of the door. 
For example, a large vision panel near the handle can noticeably affect the forces operating on the hinges in comparison with a plain door of the same weight and dimensions.
In this case the third (or forth) additional hinge at the top will provide extra support.

Door weight

- Door and frame fastening.

The materials and the jamb thickness must be able to maintain hinge stability during the door rotation.
A good hinge installation is not enough. All its elements must be perfectly installed according to the settings. The frame in particular plays an important role: it’s necessary to check it is plumb and square before installing the door as fastening the hinges may affect it. If the doors weigh > 60 Kg the screw fastening is not sufficient in such a case a mechanic fastening with screws or anchor bolt is mandatory.
Screw or anchor bolt fastening with a hinge fixing plate helps to create more stability. It is important to avoid any misalignment of the lower and upper hinge due to frame twisting.

Frame fixing

Be careful with the door width under 600mm and/or if its thickness is out of standard.
It is important to check the hinge rotation compatibility so that the door edge does not interfere with the frame while opening.


- Are the specific certificates required? Which ones?

CE branding is available in various hinges. Check the product profiles or ask Krona Koblenz for available certificates.


Conformity declaration and certificates what are they and what are they for?

Krona Koblenz

The conformity declaration is a document declared by the manufacturer that the hinge meets the requirements and current technical standards.
Krona Koblenz provides the conformity certificate for all its hinges.

Fire certifications

The fire certificate is only necessary for the use of hinges with the fire-resistant doors (REI). It certifies that the hinge installed together with the specially featured door will prevent the door from falling for a definite time (30 or 60 minutes) in case of a fire. In the product profile you will find a special symbol of the certified models by Krona Koblenz.

CE Certification

CE certification indicates that the product matches the basic safety requirements according to the standards of the building materials regulation. In particular, it refers to the mechanical resistance, dimension and colour stability, fire resistance, hygiene and environmental impact, practical safety and corrosion resistance.
Furthermore, this certificate guarantees the performance consistency as each production batch gets tested according to the required standards and validated by a third independent qualified authority which carries out serious licensed checks over our test-beds.