Choosing a suitable stove in conjunction with a twinwall flue system

 

 

It might seem counter-instinctive to consider the stove after the flue instead of vice-versa, but it is nonetheless useful to reverse-engineer the usual decision-making process because there are contingencies that vary with the flue arangements.

A twinwall flue gives you considerable leeway in positioning your stove, except in those rare circumstances, as in a thatched property with a capacious chimney, where you might install a twinwall system inside the chimney itself, in order to reduce the risk of setting fire to the roof by heat transfer through the brickwork. In such a situation, where the stove will be positioned in a masonry fireplace chamber, or when you are planning to build a fireplace around the stove, as below, your stove choice will be limited only by the fireplace dimensions, the heating requirements and the proximity of any combustible materials, such as a beam over the fireplace.

The Clearview Vision pictured below has five radiant surfaces which all get very hot in use. As a result, the walls behind and to the side need to be constructed of completely non-combustible materials. In the case of the Vision, the distance-to-combustibles is 450mm, or a foot and a half, which is, coincidentally, the same as the distance-to-combustibles for 6" single-wall flue. In the picture below, single-wall fluepipe has been deployed for the lower section of flue, both to give a more streamlined silhouette to the eventual visible installation and to allow heat from these lower sections of flue to also be distributed to the room. Insulated twinwall flue is then deployed over 450mm below ceiling height, to protect the ceiling structure from exposure to heat. As this section of flue will be boxed into the false chimney breast, the step-change in flue diameter (from 150mm to 200mm, in this case) will be concealed, leaving the appearance of a stove flued into a traditional chimney. 

Clearview Vision 500 with twinwall flue in a false chimney breast

However, it may well be that the look you are trying to achieve is more minimalist: hearth, stove, fire, flue; as in the picture below. 

Freestanding stoveContura 510 stove 100mm off a wooden wall with twinwall flue

There are two considerations to take account of here. firstly, the wall behind, in this instance, is wood. Yours may well be plasterboard, or plaster on brick. Wood and plasterboard are both combustible; plaster, while non-combustible, will crack, blow and fall off when exposed to the very high temperatures radiating from the back of a conventional stove. Stoves such as the Contura 510G pictured above are designed to overcome this specific problem, and are often referred to as 'convection stoves'. The end result of this manufacturing process is that the Contura 510 can back onto a combustible surface as close as (but no closer than) 100mm, or 4". To enjoy the benefits of the stove, you must drop the twinwall flue down all the way onto the stove, and not use single-wall flue at all. Our MF twinwall flue has a distance to combustibles of 50mm (2") so has no further impact on the positioning of the stove. (Single-wall flue has a distance to combustibles equal to three times its diameter, so in this instance, a 150mm (6")  single-wall flue would push the stove out from a combustible wall by nearly 450mm.)

There are more traditional stoves that also fit the bill; the Chesney 8-series woodburner pictured below can be installed 150mm off a combustible wall without modification, and a Clearview Solution 400 or 500, fitted with a double-rear heat shield, achieves the same. Note that in the picture below we have used single-wall flue above the stove; this is because it backs onto a non-combustible blockwork wall. 

Traditional freestandingChesney's 8-series wood burner

Another option with a traditional radiant stove is to use a rear heat shield. Building regulations have always suggested that this allows the distance to combustibles to be cut by half (plus the depth of the heat shield itself and the air gap behind), but new HETAS guidance suggests that this can be cut to 95mm for stoves 7kW and below. The Clearview 400P pictured below is installed with a blue Vlaze panel behind it, which allows it to be installed much closer to a combustible wall than would otherwise be possible. We can supply Vlaze panels in a range of sizes, colours and patterns, but you could equally use sheet steel and paint it yourself. In a domestic installation (this is a stove in our showroom, and backs onto blockwork anyway), the heat shield would also need to shield the wall from the single-wall flue pipe.

Clearview 400P wood burning stove with Vlaze metal heatshield

Along similar lines is this Chilli Billie installation in a shepherd's hut pictured below, with a proprietary enclosure to shield the wall from the stove and single-wall flue. Specifications for distances to combustibles vary from stove to stove, and with different brands and diameters of twinwall flue, so this blog is only intended as generalised guidance on those seeking stoves and flues compatible with their requirements; please, as ever, always consult your fully-qualified stove fitter or building inspector prior to any installation.

For our twinwall overview, click 'No Chimney, No Problem'

If you're weighing the merits of an internal or external flue, click 'further thoughts

Chilli Billie woodburner in a shepherd's hut

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