Natural draft flues are more than adequate for most wood fire ovens and are the preferred method of extraction for Golden Embers Ovens and, in Australia, must be installed in accordance with the building regulations applicable to open fire places in the locality where the oven is installed as well as the solid fuel appliance code.

In general, if a natural draft flue is not able to operate, you will find that there are other environmental airflow problems which will probable also cause combustion in the fire chamber to be inadequate. You must rectify these airflow problems rather than merely fix the extraction problem by fitting a fan forced unit.

Smoke is generally only produced when lighting the fire. The fumes thereafter are not unpleasant and should not aggravate neighbours or statutory authorities. Because Golden Embers ovens use so very little timber compared to others, they will only produce negligible amounts of smoke at any time. Of course, burning green or wet or resinous woods will increase the amount of smoke generated by the fire.

Where the fluing is to be directed into existing ducting or communal systems, it is important to ensure that these ducts do not have an excessive build up of fat. It will also be necessary to fit the oven with a spark-arresting device, such as Golden Embers Flame Grease and Soot Filter modules so as to eliminate the possibility of sparks being carried into the flues and igniting any fatty deposits.

A fire in the ducting or extraction system of any building can be disastrous. Because of this, wherever possible, provide a dedicated flue system for the wood fire oven.

The ductwork can become extremely hot and should be insulated wherever it is possible for patrons or staff to touch exposed sections. This can either be achieved by installing insulated ductwork or after installation by coating ducts in a vermiculite cement or insulating fire rated material. The standard installation recommended is for the use of a vented twin skin flue, and, possibly a third (often-decorative) skin in the exposed areas.

All flues must be twin skinned, with a stainless steel inner skin and a vented galvanised steel outer skin.

The standard commercial oven inner skin used is 8”  (205mm) in diameter and the outer skin is 10” (254mm) in diameter.

The standard domestic oven inner skin used is 6”  (150mm) in diameter and the outer skin is 8" (205mm) in diameter.

All penetrations through ceilings must be clear of combustible material and fitted with a non-combustible ceiling ring.

The preferred cowl is a stainless steel wood fired appliance cowl with draft diverter. A directional wood fired cowl can also be used, if preferred. In some instances you may be required to fit an AGA gas cowl, although these decrease draw and will result in more rapid build up of wood burning by-products.

The outer duct should be spaced from the inner duct by means of z spacers (or short sections of 1” square tube) at the top and bottom so as to ensure proper venting and continuous airflow.

A notch should be cut out of the outer duct to allow the damper shaft to penetrate the outer duct. A quadrant, showing open and closed positions should be fastened over the shaft and fixed to the outer duct. If a third or decorative skin (copper or brass etc.) is fitted then the quadrant should be fixed to the outside of this skin.

If gas is being used then the damper blade must either be 1/4 inch / 5mm smaller in diameter or have a notch cut off each side so as to never allow the duct to be sealed.

The outer duct must end about an inch or so lower than the inner duct and should be covered by a skirt cowl or weather spinning which does not seal it.  Alternatively you can use a wood burning twin skin cowl incorporating the outer skirt.

A 1/2 inch / 10mm high gap must be left at the foot of the second skin to allow airflow through the inter-skin gap.

The inner skin must be fitted with a steel butterfly damper with a long shaft that penetrates the second skin. Don’t use aluminium cast dampers – they warp and fall out. Use fixed shaft steel or galvanised metal dampers only.

The damper must be adjusted so that air is only just drawn into the flue. If the draw is too strong, heat will be drawn from the cooking chamber combustion will be excessive, wasting fuel and creating more soot.

If gas is fitted then the damper must either be undersized or have cut-offs to prevent absolute closure of the flue.

The damper shaft must be fitted with a lockable quadrant which shows open and closed positions.

The roof penetration must be sealed with an appropriate approved aquaseal or deck-tite. The black type is generally adequate for twin skin flues, although the pink or red types are sometimes preferred by the AGA.

Flues must clear the roof by at least 2 ft / 600mm and preferably 4 ft / 1200mm. The cowl must be at least 12 ft / 4m away from the nearest point higher than the outlet venting point.

Where the flue protrudes more than 4ft / 1200mm above the roofline, particularly in exposed weather situations, stay lines may be required to secure the flue and maintain rigidity and stability.

Where the flue is in close proximity to timbers in the ceiling space etc., the flue has been wrapped in insulating blanket, either 1" / 25mm ceramic blanket (where the exposed timbers are highly flammable) or 2" / 50mm CSR Fibretex R350.

Avoid bends and horizontal sections as far as possible and where they are absolutely necessary use 45 degree or lesser bends as opposed to ninety degree or sharper bends. Preferably use radius or lobster back bends as opposed to sharp bends. Where there is any significant extent of horizontal flue it is recommended that an inspection hatch be incorporated into the flue at the start and end of any horizontal section to facilitate cleaning and maintenance.

All bends and horizontal sections must be readily removable or fitted with inspection hatches and/or cleaning elbows.

To minimise the risk of fire, it is recommended that the flues are cleaned at least annually, to remove any soot and other build up of flammable materials, although, in reality, you will find these to be negligible if the correct timbers are used. It is advisable to have the flue inspected after six months of operation to establish what degree of build up has occurred. Where there are any horizontal sections then it is required that the flues be inspected and cleaned more regularly.

The design of the oven, tunnel and flue outlet is such as to make it near impossible for any sparks to enter the flue shaft during normal operation of the ovens. Nevertheless, where the flue is to be vented into a general or communal extraction system, it is recommended that a stainless steel baffle element filter be incorporated into the transition flue inlet and that a break be incorporated into the flue at the point of coupling, effectively creating a miniature range hood.

All flame is contained within the oven chamber and has to move out of the chamber at right angles to the induced convection flow, around a 1 3/4" / 45mm right-angled protruding lip. Thereafter, all flue gasses must move through the incoming fresh air stream, effectively inducing a vortex scrubbing effect, mix with an at least equal portion of fresh air, turn at right angles again and move into the horizontal section of the transition flue, once again change direction at right angles, before entering the flue shaft. Effectively this means all flue material moves through 320 degrees, around 4 bends, through one induced vortex and over two differing materials, before it entering the flue shaft. This design is far more effective at eliminating spark travel than the two horizontal offset strips used in competitive units (which vent directly from the cooking chamber), and which effectively put the air flue gasses through only two 45 degree bends.

Should you wish to add additional filtration, then a twin baffle insert can easily be fitted from galvanised sheet and riveted into the transition, or, a stainless flame mesh filter can be fabricated to fit into the transition intake opening. If the flame filter insert is used, it will need to be cleaned extremely regularly so as not to obstruct the airflow.

All flues must be professionally cleaned at least annually. Where bends or horizontal sections exist in the flue, or the flue vents into a common duct where fatty deposits may exist, it is recommended that they be cleaned at least six monthly and that all bends be fitted with inspection hatches. Initially clean the flues after 3 months and, if creosote build-up was minimal, then extend this period until a reasonable cycle is established.

They are fitted with thermostatically controlled and balanced twin burners, so as to heat both the air and the floor.

The by products of gas combustion do not create residue build-up, or particulate emissions, as such gas fired ovens should be treated in exactly the same manner as any other gas range or oven and can safely be vented through the standard extraction system.

Where possible, the coupling point of the gas oven should be before that of the dishwasher (if any) in the ducting scheme. Gas oven flues should be fitted with adequate dampening systems to enable efficient regulation of the exhaust and thereby minimise heat loss and maximise efficiency.

IMPORTANT: Gas fired ovens (as opposed to ovens with gas backup) cannot be fired on wood at any time or under any circumstances. In ovens with gas backup, the gas flame originates below the oven, effectively giving two separate combustion chambers, in the gas fired oven the gas combustion chamber is the oven itself, consequently no other fuel source can be used in the oven,

In all other instances, for safety reasons, follow the specifications for the wood fired ovens