Firebacks & Fireplace Lintels

Selecting Firebacks and Fireplace Throat Lintels

A traditional open fireplace must manage intense radiant heat while providing a clear route for smoke and combustion gases into the chimney. The fireback and throat-forming lintel perform different but related functions. They should be selected as compatible components within the complete fireplace layout, not simply by matching a nominal inch size.

What Each Fireplace Component Does

Component	Primary function	Selection points	Important limitation
Heat-resistant concrete fireback	Forms the heat-exposed rear surface of the open fire chamber and helps protect the masonry behind it from direct flame and radiant heat.	Nominal size, internal and external width, height, depth, fireplace opening and compatibility with the grate and lintel.	It must be installed with room for thermal movement and is not a substitute for a correctly designed fireplace, hearth or flue.
Heat-resistant fireback lintel	Works with the fireback to form the fireplace throat and guide combustion products towards the chimney.	Matching nominal size, correct orientation, throat opening and compatibility with the fireback and chimney geometry.	It is a throat-forming component, not a declared load-bearing structural lintel for supporting masonry or a chimney breast.

Fireback Sizes and Actual Dimensions

The quoted 16-inch and 18-inch designations are nominal fireplace sizes. They do not describe the fireback's overall width. Use the product dimensions to confirm the fit and allow for the specified installation clearances.

Nominal size	Internal front width	External front width	Overall height	Overall depth
16 inch	15.5 in / 39.5 cm	19 in / 48.5 cm	22.25 in / 56.5 cm	8.5 in / 21.6 cm
18 inch	17.5 in / 44.5 cm	22 in / 56 cm	22.25 in / 56.5 cm	8.5 in / 21.6 cm

Before ordering, record the width and height of the fireplace opening, the available depth, the grate or fire-basket dimensions and the position of the chimney throat. Where a drawing and a nominal label differ, use the current dimensional drawing or obtain written confirmation of the supplied component. Do not assume that an existing 16-inch or 18-inch grate will fit solely because the fireback carries the same nominal designation.

Temperature Rating and Intended Use

The concrete fireback and matching fireback lintel are listed with a maximum temperature rating of 1400°C and are intended for traditional open fireplaces. A material temperature rating identifies the stated thermal capability of the component; it does not by itself certify the performance, safety or regulatory compliance of the completed fireplace. Heat distribution, fuel load, ventilation, chimney draught, installation details and thermal cycling all affect service conditions.

These components should not be fitted to a closed stove, cassette fire, gas appliance or appliance-specific combustion chamber unless the appliance manufacturer and the responsible installer confirm compatibility. Appliance components must not be altered to accommodate a fireback intended for a traditional open fire.

Forming the Fireplace Throat

The fireplace throat is the restricted passage between the fire chamber and the chimney. Its geometry influences how combustion products enter the flue. According to the current product installation guidance, the distance between the fireback and its lintel should be 110mm ± 10mm. This dimension must be considered together with the fireplace opening and the chimney design.

The fireback lintel is installed on its curved side with the U-shaped opening facing the rear of the fireplace, as stated in the product guidance. Check the latest installation drawing before work begins, because reversing or incorrectly positioning the component can alter the throat geometry.

A throat-forming lintel does not prevent carbon monoxide from being produced. Safe removal of combustion products depends on adequate combustion air, suitable room ventilation, a correctly sized and unobstructed chimney or flue, appropriate commissioning and maintenance. A compliant carbon monoxide alarm remains essential where required by the applicable regulations.

Throat Lintel Versus Structural Fireplace Lintel

The term “fireback lintel” describes the component's position and its role in forming the fireplace throat. It must not be confused with a structural fireplace lintel used to carry brickwork, a chimney breast or another imposed load. No structural span, load-bearing capacity or reinforcement specification is stated for this product.

If masonry requires support, the opening needs a separately designed and correctly installed structural solution. The specification should be determined by a competent person who understands the existing construction, bearing length, span, loads, temperature exposure and relevant building requirements. Do not place structural loads on the throat-forming lintel unless a current, project-specific technical declaration expressly permits it.

Allowing for Thermal Expansion

Firebacks repeatedly heat and cool, so they must not be rigidly trapped by the surrounding masonry. Provide expansion allowance at the back and sides in accordance with the current product instructions. A restrained refractory component is more likely to develop stress cracking or displace adjacent work during thermal cycling.

The published installation method uses a corrugated-cardboard spacer around the rear of the fireback to establish an expansion gap during construction, followed by filling the void behind it with Vermiculite Insulating Cement. The space above the fireback and below the rear chimney area is then formed with Heatproof Screed. At the front, the gap between the fireback and the fireplace surround is packed with suitable lagging rope and finished with an appropriate heat-resistant sealant. These materials perform different functions; do not replace the compressible seal with a rigid mortar joint.

Follow the latest instructions for the exact products used, including mixing, application thickness, curing and temperature limits. Keep the fireback and all installation materials dry before use. Existing damp, salts, loose masonry and old mortar should be assessed and remedied before the new components are fitted.

Drying and First Firing

Moisture retained in the fireback, insulating fill or surrounding construction must be released gradually. Store the components under cover before installation. The product guidance states that a fireback taken from open storage should not be fired for three days after installation. Longer drying may be necessary where the supporting materials, ambient conditions or project specification require it.

Begin with a small, short-duration fire and allow the assembly to cool. Increase the duration and intensity in stages over subsequent firings. Sudden high heat applied to damp or newly installed refractory material can cause steam pressure, excessive thermal stress, cracking or surface damage. Never use a powerful fire to accelerate drying.

Ventilation, Chimney Condition and Commissioning

An open fire draws combustion air from the room and discharges combustion products through the chimney. Before use, a competent installer or chimney professional should check the air supply, flue route, terminal, draught, hearth, proximity to combustible materials and condition of the fireplace. The chimney should be swept and inspected for blockage, leakage and unsuitable liners or terminals.

After installation, verify that smoke enters the flue without spilling into the room under the relevant operating conditions. Changes such as replacement windows, extractor fans or alterations to adjoining rooms can affect the available air and chimney performance. Stop using the fire if smoke or fumes enter the room, a carbon monoxide alarm activates, components move, or significant cracks and open joints develop. Ventilate the space and obtain competent advice before relighting.

Inspection and Maintenance

• Inspect the fireback, lintel and surrounding joints before the heating season and at suitable intervals during use.
• Look for displacement, widening cracks, loose material, failed seals and gaps that could allow hot gases to reach surrounding construction.
• Keep the chimney and fireplace free from soot, debris and obstructions through an appropriate sweeping schedule.
• Replace degraded lagging rope or sealant with materials suitable for the location and service temperature.
• Investigate repeated cracking or smoke spillage rather than covering the symptom with additional mortar or sealant.

Frequently Asked Questions

What is a fireplace fireback?

A fireback is a heat-resistant component that forms the rear surface of the fire chamber in a traditional open fireplace. It shields the masonry behind it from direct flame and intense radiant heat.

What does a fireback lintel do?

The matching fireback lintel helps create the fireplace throat between the fire chamber and chimney. It guides combustion products towards the flue when correctly positioned within a suitable fireplace design.

Are the fireback and fireback lintel used together?

Yes. They are complementary components, and the nominal size and geometry should correspond. Check the dimensions of both items and the complete fireplace arrangement rather than relying on the size name alone.

Should I choose the 16-inch or 18-inch fireback?

Choose according to the measured fireplace opening, grate, available depth and matching lintel, not merely the historic description of the fireplace. The 16-inch fireback has an internal front width of 15.5 inches, while the 18-inch version has an internal front width of 17.5 inches.

Is the nominal size the fireback's overall width?

No. The 16-inch model is approximately 19 inches wide externally at the front, and the 18-inch model is approximately 22 inches wide. Consult the full dimensions before ordering.

What is the maximum listed temperature?

Both category products are listed with a maximum temperature rating of 1400°C. This is a material or product rating and must not be treated as a guarantee of the completed fireplace's performance.

Is the fireback lintel load-bearing?

It should be treated as a throat-forming component, not as a structural lintel. The product information does not state a structural load rating, permissible span or reinforcement specification. Masonry support must be designed separately where required.

Does the fireback lintel prevent carbon monoxide?

No. It helps establish the fireplace throat but cannot prevent carbon monoxide formation. Adequate air supply, a suitable and maintained chimney, correct installation, commissioning and a compliant carbon monoxide alarm are essential safety measures.

Which way round is the fireback lintel installed?

The product guidance states that it sits on its curved side, with the U-shaped opening facing the rear of the fireplace. Confirm the orientation against the latest supplied instructions before installation.

What gap is required between the fireback and lintel?

The published fireback instructions specify a throat distance of 110mm ± 10mm between the fireback and lintel. The complete fireplace and chimney geometry must also be suitable.

What should be installed behind the fireback?

The product method specifies an expansion gap and Vermiculite Insulating Cement behind the fireback. The installation must follow the current instructions and maintain the required allowance for thermal movement.

Why does a fireback need expansion space?

The refractory component expands when heated and contracts as it cools. A suitable gap reduces restraint and the resulting mechanical stress on the fireback and adjacent masonry.

How should the fireback be sealed to the surround?

The specified front detail uses suitable lagging rope as a compressible packing, followed by heat-resistant sealant. A rigid mortar joint should not replace the flexible sealing arrangement where movement must be accommodated.

When can I light the first fire?

Allow all components and installation materials to dry in accordance with their instructions. Where the fireback has been kept in open storage, the product guidance states that it should not be used for three days after installation. Start with a small fire and increase the heat gradually over later firings.

Can these parts be used in a closed stove or cassette fire?

They are intended for traditional open fireplaces. Do not install them in a closed or appliance-specific combustion chamber unless the appliance manufacturer and a competent installer have confirmed that the application is suitable.

Which British Standard applies to open fireplace components?

BS 1251:2015 is the current British Standard for open fireplace components, including firebacks and throat-forming lintels. Any reference to BS 1251:1987 is a legacy reference because that edition has been withdrawn. Obtain current conformity documentation where compliance with a particular edition is required.

When should a fireback be professionally inspected?

Arrange an inspection if the fireback or lintel moves, a crack widens, material becomes loose, sealing joints fail, smoke spills into the room or a carbon monoxide alarm activates. Stop using the fireplace until the cause has been identified and corrected.