Concealed door hinges are what make a flush, frameless or “invisible” door look the way it does. With ordinary butt hinges you always see the knuckles on one side of the door. With concealed hinges, the hardware is hidden inside the door edge and the frame, so when the door is closed there is nothing on show but a clean, painted surface.

This guide covers the main types of concealed hinge for internal doors, how to read load ratings, door thickness, fire door rules and practical fitting tips.

What are concealed door hinges?

A concealed hinge is mortised (recessed) into the edge of the door leaf and into the frame, rather than screwed onto the surface. When the door closes, the two halves of the hinge fold away inside the door and frame, so you can’t see them from either side. They only become visible when the door is open.

They’re used on concealed, flush to wall and frameless doors, on jib doors in period rooms, and on contemporary doors where you simply want a cleaner look. If you’re new to the terminology, our guide to jib doors, concealed, frameless and flush to wall doors explains how the terms overlap.

A quick note on “concealed bearing” hinges

You’ll sometimes see “concealed bearing” butt hinges in ironmongery catalogues. Despite the name, these are not hidden hinges. The word “concealed” refers to the bearings inside the knuckle. The knuckle itself is still visible on the face of the door.

Not the same as cupboard hinges

The small cup hinges used on kitchen cabinets are designed for lightweight cupboard doors, not full-size room doors. This guide covers hinges for internal doors only.

The main types of concealed door hinge

3D adjustable concealed hinges

This is the most common type for modern concealed doors. Each hinge has two bodies, one routed into the door edge and one into the frame, linked by a folding arm. Once fitted, you can fine-tune the door in three directions using an Allen key:

Height: raising or lowering the leaf to even out the gap at the head and floor
Side to side: moving the leaf towards or away from the hinge side to balance the gaps
Compression (in and out): pulling the leaf in or pushing it out so it sits flush with the frame and wall

That third adjustment is especially important on flush to wall doors, because even a millimetre or two of misalignment shows up when the door and wall are painted the same colour.

Self-closing concealed hinges

Some 3D concealed hinges include a closing mechanism, so the door swings shut on its own without a surface-mounted closer. The Atlantic AGB Eclipse 3.2 heavy duty self-close concealed hinge we stock is rated for doors up to 60kg, and the manufacturer specifies only one self-closing hinge per door, with standard AGB Eclipse 3.2 hinges used for the other positions.

They’re handy for utility rooms and cloakrooms, but they aren’t automatically suitable for fire doors (see below).

Hinges supplied as part of a concealed door set

Most concealed door frames are sold as a system, with the hinges already matched to the frame and the door leaf machined to suit. For example, our Concealed Omega Primed Door Set comes with hidden hinges built into the leaf and frame, and the Frameless Hidden Door is supplied with three-way adjustable hinges, hinge cover plates, a magnetic latch and seals. If you’re buying a complete set, you normally don’t need to choose hinges separately.

How to choose the right concealed hinge

1. Work out the real door weight

Every concealed hinge has a maximum load rating. Start with the weight of the door leaf, then add anything that increases the load:

Cladding or panelling: wall panels, mirrors or timber cladding stuck to the face add weight quickly
Door closers: according to guidance in the hinge standard BS EN 1935, as quoted by hardware supplier Better Building Hardware, a closer without opening suspension effectively increases the door weight by 20%, and one with opening suspension by much more
Size: wide and tall leaves put more leverage on the top hinge, even at the same weight

Always choose a hinge with a comfortable margin over your calculated figure, rather than one that only just covers it.

2. Check how the rating is quoted

Manufacturers usually quote load capacity for a set number of hinges. Acorn Ironmongery’s selector chart for Ceam 3D hinges, for instance, lists the 1130 model at 40kg with two hinges and 60kg with three. Other makers state that adding a third or fourth hinge does not necessarily increase the rated capacity. Don’t assume. Read the data sheet for the specific hinge, and ask the supplier if your door is close to the limit.

3. Match the hinge to the door thickness and frame

Concealed hinges need a deep mortise, so each model has a minimum door thickness. The hinge body has to fit inside the leaf with enough timber left either side to hold the screws. Standard UK internal doors are typically 35mm or 44mm thick, and many concealed systems use 44mm or thicker leaves. Our SF-LINE aluminium flush frame, for example, specifies a minimum door thickness of 40mm.

The frame matters too. Hinges designed for aluminium plaster-in frames aren’t always interchangeable with those for timber frames, so stick to the hinge specified by the frame manufacturer.

4. Think about the finish

When the door is closed you won’t see the hinge, but when it’s open you will. Common finishes include satin nickel, matt chrome and matt black. We stock LPD Eclipse matt black concealed hinges and matt chrome concealed hinges, both sold in pairs.

5. Decide on the latch at the same time

Concealed doors usually pair concealed hinges with a quiet magnetic latch, or a push-to-open touch latch for a handleless door. Choose hinges, latch and handle together so the finishes match.

Concealed hinges on fire doors

This is where you need to be careful. If the door is a fire door, the hinges are part of its fire performance.

Marking: ASSA ABLOY’s guidance states that hinges fitted to fire doors are legally required to be UKCA or CE marked to EN 1935.
Number of hinges: the same guidance says fire doors need three hinges to meet UK fire door standards and regulations.
Test evidence: a concealed hinge can only be used on a fire door if the door manufacturer’s test evidence covers that hinge. Fire door maker Forza’s ironmongery guide, for example, lists specific concealed hinge models it has assessed, requires factory-prepared leaves and frames, tight-fitting hinge slots and the hinge manufacturer’s intumescent kits at every hinge position.

In practice, that means you shouldn’t retrofit concealed hinges to an existing fire door yourself. If you need a fire-rated concealed door, buy a tested set. Our Invisible Frameless Hidden Concealed FD30 Fire Door is supplied as a complete set with hinges and intumescent kits. For more on fire ratings, see our guide to internal fire door types.

Fitting and adjustment tips

Get the mortises right. Concealed hinges need precise, deep routing in both door and frame. Most concealed door sets arrive pre-machined; if you’re preparing your own, a routing jig made for the hinge model is essential.
Hang, then adjust. Fit the door, check the gaps all round, then use the 3D adjustment to get the head gap even and the face flush. Small adjustments on each hinge make a big difference.
Check plumb first. Adjustment can hide minor errors, but it can’t fix a frame that’s badly out of plumb. If the frame isn’t true, the door may swing open or shut on its own.
Recheck after a few weeks. New doors and fresh plaster can settle slightly. A quick tweak keeps everything aligned, and if the door ever starts to drop at the lock side, check the hinge adjustment and the door weight.

Frequently asked questions

How many concealed hinges does a door need?

It depends on the hinge model, the door size and its weight. Many concealed door systems use three hinges per leaf, and fire doors need three. Always follow the hinge manufacturer’s data sheet for the number and position of hinges.

Can I fit concealed hinges to my existing internal door?

Sometimes, if the door is thick and solid enough to take the mortise and the frame can be routed to suit. It’s precise joinery work, though, and hollow-core doors usually aren’t suitable. For a truly flush look, a purpose-made concealed door set is normally easier and more reliable.

Are concealed hinges strong enough for heavy doors?

Yes, as long as you choose a model rated for the weight. Load ratings vary widely from one hinge to another, so check the figure, allow for cladding and closers, and leave a margin.

Can concealed hinges be painted?

Some can. LPD describes its Eclipse matt black concealed hinge as easy to paint to match a colour scheme. In most cases it’s simpler to choose a finish you like, since the hinge is hidden when the door is closed.

Do concealed hinges work on fire doors?

Only when the fire door’s test evidence covers that hinge, with the correct intumescent kits fitted. The hinges must also be UKCA or CE marked to EN 1935. Buy a tested fire door set rather than adapting a door yourself.

Find the right hinges for your door

Whether you need a single self-closing hinge or a complete concealed door set with matched hardware, we can help you choose. Browse concealed door hinges and magnetic latches, or explore our full range of concealed and flush to wall doors.