Learn what an intumescent letterbox is, how it works, and when it should be used on fire doors.
Written by Esme
6th October 2021
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In its simplest terms, an intumescent letterbox is a letterbox that’s used in a fire door.
It features an intumescent liner that, in the event of a fire, expands and seals off the letterbox opening thus preventing the transmission of fire and smoke from one room to another. Using intumescent sealant will add further fire protection to your door by sealing linear gap joints on your door.
When would you need an intumescent letterbox?
You would need to use an intumescent letterbox whenever you want to install a letterbox in a fire door.
One most common application is in flats and high rise buildings where an internal door can function as a front door to a residential home and these also often fire doors. In these instances, an intumescent letterbox must be used to ensure the fire door retains its integrity and function in the case of a fire.
How to fit an intumescent letterbox
Measure the size of the central telescopic section of the letterbox, including the intumescent liner, to determine the size of cut out needed
Cut an aperture in the fire door up to 1050mm from the bottom of the door. Ensure that this is a tight fit to allow the fixing of wood screws in the corner of the face plates
The face plate with the draught excluders should be fitted to the internal face of the door
Place the letterbox into the aperture created and secure in place using steel wood screws
To maintain the fire proof integrity of the door, ensure any gaps between the letterbox and the aperture are sealed using intumescent sealant
It’s important to note that a regular letterbox cannot be made into an intumescent letterbox purely by adding intumescent material around it as this hasn’t been tested in a fire situation.
How We Can Help
At FireSealsDirect, we stock a wide range of intumescent letterplates in various sizes and finishes to suit your fire door requirements.
If you need any guidance, our expert team is always happy to help. You can reach us at [email protected] or by calling 02920 85 969.
