Patraña Oncena de Joan de Timoneda
III. 3. Antíoco y su hija
Heat producing appliances include all types of stoves, fireplaces, boilers for central heating and the like.
According to the Building Regulations for Small dwellings, heat producing appliances and
chimneys shall be so constructed that they cause no danger of fire, explosion, poisoning or other health hazards. Materials used must be resistant to flue gases, fire, heat and corrosion.
This chapter deals with the installation of heat producing appliances and chimneys used for oil and solid fuel heating. Regarding the installation of gas heat producing appliances and flue ventilation reference is made to regulations in
“Gasreglementet”, section A, 1991, 1st amendment, March 1991 and 2nd amendment, May 1995, “Danmarks Gasmateriel Prøvning”
(Danish institute for the testing of materials used in gas installations).
This SBI-direction does not cover special rules applying to the installation of oil tanks and pipes for oil supply.
Heat producing appliances
When heating with solid or liquid fuel a clear distinction is made between closed and open heat producing appliances. In an open heat producing appliance it is not possible to close the hearth with doors or similar from the room, which is to be heated. Closed heat producing appliances are central heating boilers as well as stoves equipped with doors.
The size of a closed heating appliance is characterised by the stoking effect, that is, the heating effect released at combustion. The stoking effect is proportional to the consumption of fuel. When stoking with oil the stoking effect is approximately 10 kW at a consumption of 1 litre of oil per hour, and when stoking with solid fuel the equivalent
value is 4 kW at a consumption of 1 kg wood per hour.
When pressure atomising burners are used for oil heating the effect is determined by the
ejector nozzle size. It is difficult to determine the exact stoking effect of manually fed stoves and boilers (solid fuel) given the fact that feeding tends to be uneven and uncontrolled. A small stove can have a maximum wood
consumption of 3 kg per hour and thus have a stoking effect of 12 kW. Any stove produced and tested according to DS 887, “Solid fuel stove for room heating - Part 1: Requirements”
will have a stove label containing information about the nominal effect in kW.
Setting up
Heat producing appliances can be set up in living rooms, kitchens, sculleries and basement rooms provided the ventilation is sufficient to give adequate air for combustion. This can for example be achieved by supplying the room with an adequately dimensioned adjustable fresh air vent or by supplying combustion air
through a ventilation duct from the outside.
Installation of heat producing appliances on, or close to combustible material, is allowed provided the heat emission does not cause temperatures in excess of 80oC on any combustible material.
In the case of fireplaces and stoves this requirement is considered to be fulfilled when the distance from any exterior part of the fireplace or stove to combustible material is at least 500 mm. In the case of masonry fireplaces this distance is measured from the internal surface of the fireplace. Stoves constructed in accordance with DS 887 can be installed
according to the distances specified on the stove label.
Safety distances are always calculated to combustible material whether visible or concealed behind a non-combustible covering.
The distance requirements do not apply to skirtings.
The floor below stoves and fireplaces must be combustible or firmly covered by a non-combustible material such as stone or stone aggregate or a steel or copper plate to protect against falling embers. The covering shall extend at least 300 mm in front of closed hearts
and at least 500 mm in front of open hearts.
Furthermore, the covering shall extend at least 150 mm to either side of the hearth opening.
Connection to chimney
Heat producing appliances for solid and liquid fuel shall always be connected to a chimney extending above the roof. The connecting pipe between the heat producing appliance and the chimney is called a flue pipe.
Flue pipes must be installed in such a way as to facilitate easy maintenance and cleaning. Flue pipes should be short and with as few elbows or curves as possible. When cleaning cannot be done via the heat producing appliance, the flue pipe shall be equipped with sufficient cleanout doors.
Inside the room where the heating appliance is installed, flue pipes less than 1.0 m long can be made from minimum 1.0 mm steel plate or similar. When pipes are longer than 1.0 m, a thicker plate should be used, for example 2.0 mm.
The clearance between non-insulated flue pipes and combustible material shall be at least 300 mm.
When two or more heating appliances are connected to opposite sides of the chimney the connection shall be continuous in such a way that the vertical distance between connections shall be at least 250 mm.
An open fireplace shall be connected to a separate chimney with no other connections from heating appliances. Gas heating appliances shall be connected to a flue according to the regulations stated in “Gasreglementet” (the Gas Regulations).
Chimneys
Chimneys shall be sufficiently high to ensure adequate flue. Also, chimneys shall be sufficiently high (in relation to roofs and
surroundings) to ensure that the smoke is quickly dispersed and diluted into the atmosphere.
Cross-sectional area
The cross-sectional area of the chimney must be adjusted to the amount of smoke. The cross sectional area must be sufficiently large to
accommodate for maximum smoke flow. Also space must be reserved for soot deposit. On the other hand the cross sectional area must not be excessively big as this may result in
condensation and tarry soot. Stoking with solid fuel requires a larger cross sectional area than oil combustion.
The cross sectional area should be kept within the limits stated in figure 107 for oil stoking and solid fuel stoking. In case of circular cross sections the limits equal the limits of the diameter stated in figure 108.
The dimensioning is based on the stoking effect of the connected heating appliance or on the total effect of all connected heating appliances.
When both oil and solid fuel stoked heating appliances are connected to the same chimney the cross sectional area can be determined as a compromise between the stated values for oil stoking and solid fuel stoking. However, it will usually be a better solution to connect the appliances to separate chimneys.
Figure 107: Cross sectional area limits for small chimneys used for oil and solid fuel stoking. Sizes are determined as a result of the total stoked effect at maximum load. The bold horizontal lines represent minimum
requirements in Building regulations for Small Dwellings. The values apply to closed heating appliances
Solid fuel
Oil
Chimney cross sectional area cm2
Stoking effect, kw
SBI Direction 189,
KLJ 98
Figure 108: Limits for the internal diameter of small chimneys with a circular cross section -oil and solid fuel stoking. The bold horizontal lines represent minimum requirements in
Building regulations for Small Dwellings. The values apply to closed heating appliances.
Example: An oil stoked central heating boiler consuming 2 litres of oil per hour (with oil burner active) has a stoking effect of 20 kW. As stated in the figure the diameter should not be chosen below 100 mm and not above 140mm. If a stove is also connected with a maximum consumption of 4 kg wood per hour the total effect is 36 kW and a diameter of 175 mm can for example be chosen.
The cross sectional area of the chimney and the flue pipe to which an open fireplace is connected shall be at least 300 cm2. If the free opening of the fireplace is not larger than 2500 cm2, the cross sectional area can be reduced to 175 cm2. The free opening refers to the opening through which the combustion air is flowing into the heating appliance. When the heating appliance is
equipped with openings on several sides the area is measured as the sum of all openings. Cross sectional areas of 300 cm2 and 175 cm2
correspond to diameters of 195 mm and 150 mm respectively.
Height
A slight negative pressure should be established in the combustion chamber of a heating
appliance and in the entire flue system - not only for the sake of smoke transportation but also for safety precautions by preventing smoke drifting from the heat appliance, the flue pipe or the chimney into the surrounding rooms. The low pressure is established by the thermal buoyancy created by the hot smoke in the chimney. The buoyancy increases with higher smoke temperature and by increasing the chimney height. The chimney of an oil furnace/boiler must suck out the smoke from the boiler while the oil burner fan supplies the combustion air.
When stoking with solid fuel the chimney must not only suck out the smoke from the heating appliance - it must also suck the combustion air into the heating appliance through the air intake.
Stoves and especially central heating boilers for solid fuel therefore often require higher
chimneys than oil furnaces.
The chimney height is calculated from the floor on which the heating appliance is placed.
Whenever possible, the height should not be less than 5 m. In the case of solid fuel boilers and other heating appliances requiring higher chimneys in order to function safely the manufacturer’s instructions should always be followed.
When a house is exposed to wind an over-pressure occurs on the windward facade and – at roof pitches above 30oalso along the lower part of the roof. The chimney should be sufficiently high to secure that the outlet is placed outside the over-pressure zone. Smoke eddies tend to arise above flat roofs and in the lee side of pitched roofs. Consequently, smoke may be lead down to a level where humans breathe and thus cause inconveniencies. Therefore, the chimney should be taken up above the eddy zone. As a rule-of-thumb the chimney is usually taken up 1 m above the roof ridge or the highest part of the roof. The chimney outlet should under no circumstances be placed lower than the highest point of the roof. If the chimney is placed on a low extension, the height of the chimney shall be determined according to the highest roof ridge of the house.
Solid fuel
Oil
Stoking effect, kw
Chimney cross sectional area cm2
Construction
Brick chimneys are traditionally constructed with a 252 x 252 mm cross sectional opening and a 108 mm chimney wall inside the house and a 228 mm wall in the chimney pot. This construction is rarely used in new buildings partly because the cross sectional area is too large and partly because the insulation is too poor but also because the wall construction method may cause leakages. Instead bricked chimneys are made either of pre-cast liner elements which can be brick clad or as a traditional brick chimney but with an insulating lining which reduces the cross sectional area, see figure 109. The figure also shows an example of a steel chimney.
Chimney elements and chimney linings as well as steel chimneys shall be MK approved and
construction/installation shall be carried out in accordance with manufacturer’s instructions.
Figure 109
Examples of chimney cross sections. The figure shows examples of chimney elements and chimney linings. Other types of elements and linings do exist. However, all elements and linings must be MK-approved.
a) Thin-walled lining: to be lowered into existing brick chimney.
b) Thick-walled lining: built-in during the construction of a traditional brick chimney.
c) Pumice concrete element where the cavity is filled with a lean clinker concrete.
d) Ceramic tile/ concrete element with air filled cavities.
e) Ceramic tile/ concrete element with mineral wool in cavity.
f) Steel chimney.
g) Pumice concrete element with air filled cavities.
Chimneys are usually cleaned from the top. In houses with non-habitable attics above the collar beams it is, however, practical to
construct the chimney in such a way that it can be cleaned from a cleanout door in the attic.
Care must be taken to secure safe access for the chimneysweeper to the chimney. It may be necessary to mount steps on the roof and to equip tall chimney pots with corrosion protected rungs. The mounting of rungs is only possible on solidly build chimney pots. Rungs cannot be mounted on prefabricated chimney elements and safe fixing in masonry is only possible provided the brickwork has a minimum thickness of 228 mm.
During cleaning the soot is swept down inside the chimney. This soot must be removed through a cleanout door at the bottom of the chimney. When a steel chimney is mounted directly on top of a furnace the soot is swept down into the furnace which will then be cleaned together with the chimney.
When a chimney is not constructed vertically it may be necessary to install extra cleanout doors.
Cast iron double cleanout doors are used for brick chimneys.
The clearance between combustible material and steel or brick chimneys shall be at least 100 mm.
Clearance between cleanout doors and
combustible material shall be at least 200 mm.
Distances are measured from the external side.
Beams, rafters and stair stringers may however be placed directly against brick chimney walls provided the wall is at least 228 mm thick or provided the chimney is constructed similarly, for example a chimney element with at least 108 mm brick cladding or as a brick chimney with a 108 mm wall supplied with a lining. In the latter case the chimney must be insulated from any combustible material using at least 20 mm mineral wool.
The edge of combustible claddings with a maximum thickness of 30mm can be placed directly against brick chimneys. The distance to steel chimneys shall be at least 50 mm.
Thatched roofs
In roof coverings which cannot be classified as a class T roof covering like for example thatched
SBI Direction 189,
KLJ 100
roofs, chimneys shall be so constructed and installed that adequately fire safety is achieved.
Brick chimneys: From minimum 300 mm below the roof cover and upwards the walls shall be constructed of at least 228mm masonry or of approved chimney elements clad with at
minimum 108 mm brickwork. Under the roof the masonry shall be protected against cracks by application of at least 30 mm reinforced plastering.
Steel chimneys: From minimum 300 mm below the roof cover and upwards the chimney shall run through a duct, which has a diameter of at least 200 mm more than the diameter of the chimney.
Chimneys erected within a distance of 6m from a thatched roof or other easily combustible roof material shall be extended at least 0.8 m above the roof ridge and should not be equipped with chimney covers, chimney caps, chimney spark arresters or the like as such devices may result in increased risk of fire spread if a chimney fire occurs.
For more details on the fireproofing of thatched roofs reference is made to “Brandteknisk
Information nr. 29, Brandsikring af stråtage” (Fire technical information no 29, Fireproofing of thatched roofs, The Danish Institute for fire testing)