FIRTH CHIMNEYS AND OPEN FIREPLACES
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3132
FIRTH CHIMNEYS AND
December 2010
OPEN FIREPLACES
Precast open fireplaces continue to enjoy popularity with many
architects and builders, because of their aesthetic appeal and ease
of construction.
HOW IT WORKS
Room air is drawn into the fire chamber and through Foundation
the fuel bed, thereby supplying oxygen for the burning
The foundation should be excavated into naturally
process. Combustion gases and smoke rise from the
solid ground (never less than 300mm deep) and be
burning fuel to the throat and then through the flue to
of a sufficient area to ensure stability. The foundation
the outer air. A correct balance between the sizes of
pad should be of reinforced concrete never less than
fire chamber, throat, flue cross sectional area and flue
150mm thick.
length are essential to a continuous upwards discharge
draft of combustion gases and smoke. Satisfactory
Flue
dispersal of combustion gases and smoke could be
impeded by a flue being too big or too small in relation The height of the chimney shaft above the roof line
to the size of the fire chamber. should be greater than 600mm and less than 2400mm
above the highest part of the roof intersect. The top of
the chimney has to be more than 1500mm from the
nearest point of the roof measured horizontally.
Flue Height
The maximum height for a sectional pumice chimney
Lintel
is 9140mm, measured from the ground to the highest
point of the chimney cap.
Mantle
Gathering
Surround Supports
Our sectional pumice chimneys should be secured to
Smoke Shell
the building at the ceiling, the roof line and at each
floor level with galvanised metal straps, at no less
Throat
than intervals of 2.4 metres. Suitable provision will
need to be included in the design of individual houses
Fire back
to ensure that they possess adequate strength to resist
Front
Hearth the horizontal wind and seismic loads which will be
Fire chamber
transferred into the house frames from the chimney.
Grate
Tip Plate & Frame Mortar Joints
Ash-dump
Hob To join the pumice sections together, a full bed of
premixed mortar should be used.
Back
Hearth
Standard
The means of compliance is NZS 1900, chapter 7
cover manufacturing and safety requirements for open
fireplaces and small chimneys.
Reinforcing Base Slab
The chimney should have continuous vertical reinforcing The base on all chimneys for an outdoor setting must
consisting of four 12mm deformed steel rods. The have a base larger than the chimney. This is to prevent
reinforcing extends the full length of the chimney above the chimney from falling over. An engineer should be
the gathering. All reinforcing should be grouted with consulted to provide the correct dimensions for this
a high strength low shrinkage pourable cementicious base.
grout.
Chimney Selection
Fire back The chimneys approved for an outdoor setting are;
Fire bricks should be laid on the flat using a refractory
• Super Heat Master chimney
mortar, the sides of the fire chamber should be vertical,
• Standard Log Burner chimney
but in plan view should be angled so as to reduce the
• Super Log Burner chimney
back width of the chamber, this back width should be
• Super Room Warmer chimney
the same as that of the chosen grate.
FOR ALL NON STANDARD APPLICATIONS AN
The fire back should rise vertically for the first
ENGINEER SHOULD BE CONSULTED.
150mm and then slope forward in a straight line
towards the throat.
The fire back must not be laid with a cruve as it rises, Timber
Framing
because this could cause smoke to be curled forward
Cement
Compo.
of the lintel and into the room. There should be a space
between the structural chimney and the fire back, this
space being filled with fine dry pumice and capped with
a smoke shelf which shall be dished. Air Tight TW
Seal
Throat
TH
The throat should be the full width of the fire chamber As
and relatively narrow e.g. between 90mm and 100mm. Narrow
Strai Curved)
Fireb
As Possible
(Not
The fireback should rise at least 75mm higher than the
ricks
ght S
lintel.
H
lope
Outdoor Chimney
For the outdoor chimney to draw properly, a minimum D
height of between 2.6 - 3.0m is recommended. For
finishing - we recommend plastering outdoor chimneys
only.
Fine Shingle
Bracing Requirements Filling
The maximum a chimney can be built free standing
without bracing is 2.4 metres. Because of the reinforcing
detail both the Log Burner chimneys require a wing
wall built behind the chimney for bracing purposes. The
Log Burner chimneys require bracing for the bases, sill
block rectangle, sill block gathering and in the case of
the Standard Log Burner the extension gathering as
well. Above this wing wall, 2.4 metres of freestanding
flue blocks including the cap can be installed.
Inside
260 x 150 230 Standard Flue Cap
390 490
Inside
335 x 230 150 Standard Flue Block
410 510
395 Extension Gathering
400 1090
Deflector
250
570 1090
Standard Heat Master Chimney Base Section
Base Section Standard Flue Cap 710
Rectangle Gathering Firebricks (80) 890
Extension Gathering Steel Rod D12 (10 metres) 570 1090
Standard Flue Blocks Refractite Cement (16kg)
Note: Steel is not supplied.
Inside Super Flue Cap
260 x 150 70 1090
410
Inside Super Flue Block
350 x 250 150 1090
410
Open Gathering
300 1090
405
Deflector
250
570 1090
Base Section
710
Super Heat Master Chimney
890
Base Section Super Flue Cap
570 1090
Rectangle Gathering Firebricks (80)
Open Gathering Steel Rod D12 (10 metres)
Super Flue Block Refractite Cement (16kg)
Note: Steel is not supplied.
Reinforcement Details
210
Hole Size 50mm dia.
300
65
50 50
300 400 300
Inside
260 x 150 230 Standard Flue Cap
390 490
Inside
335 x 230 150 Standard Flue Block
410 510
380 Extension Gathering
400 1090
Sill Block Gathering
300
1600
405
Sill Block Rectangle
300
1600
Standard Log Burner Chimney 580
Base Section Lower Standard Flue Block Base Section Upper
Base Section Upper Standard Flue Cap
1410 600
Sill Block Rectangle Firebricks (120) 355 1
Sill Block Gathering Steel Rod D12 (10 metres) 590
Base Section Lower
Extension Gathering Refractite Cement (24kg)
355 1410 600
1
Note: Steel is not supplied. 590
Super Flue Cap
70 1090
410
Super Flue Block
150
1090
410
Still Block Gathering
1100
300 1600
410
Still Block Rectangle
300
Super Log Burner Chimney 1600
580
Base Section Lower Super Flue Block Base Section Upper
Base Section Upper Super Flue Cap
Sill Block Rectangle Firebricks (120) 360 1410 600
1
Sill Block Gathering Steel Rod D12 (10 metres) 590
Base Section Lower
Refractite Cement (24kg)
360 1410 600
1
Note: Steel is not supplied. 590
Reinforcement Details
60
Hole Size 50mm dia.
460 crs
60
60 60
1470 crs
Inside
260 x 140 230 Standard Flue Cap
390 490
Inside
335 x 230 150 Standard Flue Block
410 510
430 Extension Gathering
560 1090
Deflector
250
570 1090
Standard Fireglow Chimney Base Section
Base Section Standard Flue Cap 710
Deflector Firebricks (80) 890
Extension Gathering Steel Rod D12 (10 metres) 570 1090
Standard Flue Block Refractite Cement (16kg)
Note: Steel is not supplied.
Inside Super Flue Cap
260 x 150 70 1090
410
Inside Super Flue Block
350 x 250 150 1090
410
Open Gathering
300
1090
405
Deflector
250
570 1090
Base Section
710
Super Fireglow Chimney 890
Base Section Super Flue Cap 1090
570
Deflector Firebricks (80)
Extension Gathering Steel Rod D12 (10 metres)
Super Flue Block Refractite Cement (16kg)
Note: Steel is not supplied.
Reinforcement Details
210
Hole Size 50mm dia.
300
65
50 50
300 400 300
Inside
240 x 140 230 Standard Flue Cap
390 490
Inside
335 x 230 150 Standard Flue Block
410 510
430 Extension Gathering
600 1095
Gathering Slab
76
1244
600
Deflector
485
Standard Room Warmer Chimney 1040
Base Section Standard Flue Cap 1244
600
Deflector Firebricks (80)
Gathering Slab Steel Rod D12 (10 metres) Base Section
Extension Gathering Refractive Cement (16kg) 480
1040
Standard Flue Blocks 1244
600
Note: Steel is not supplied.
Super Flue Cap
Inside
260 x 150 75 1090
410
Super Flue Block
Inside
150
350 x 250 1090
410
Open Gathering
300
1090
410
Gathering Slab
75
1244
600
Deflector
485
1040 4
124
600
Super Room Warmer Chimney
Base Section Super Flue Cap Base Section
Deflector Firebricks (80) 480
1040
Gathering Slab Steel Rod D12 (10 metres) 1244
600
Extension Gathering Refractive Cement (16kg)
Super Flue Blocks
Note: Steel is not supplied.
50
Reinforcement Details
50
Hole Size 50mm dia.
50
120 120
300 400 300
TECHNICAL SPECIFICATION - CHIMNEY FOUNDATION
Figure 1
300mm
lap
75mm hearth slab
D10 at 255mm ctrs each way 500mm
Timber floor (double joists
max each side of hearth slab)
Floor line for
internal chimney
Foundation for base
300mm
300mm D12 at 400mm ctrs (300mm legs)
lap
lap
D12 starters at 400mm
max ctrs to match
150mm R6 U bars at 200mm ctrs in walls
vertical rods in chimney
300mm
min
200mm
min
Chimney foundation slab.
D12 at 300mm ctrs each way
or 661 mesh top and bottom
300mm leg
(A) Suspended Floor
300mm
lap
D12 starters at 400mm 400mm lap
max ctrs to match
vertical rods in chimney Ground Floor Slab
150mm
Floor line for
internal chimney
Chimney foundation slab.
D12 at 300mm ctrs each way
or 661 mesh top and bottom
D12 at 400mm ctrs max (300mm leg)
(B) Slab On Ground Lap 400mm with slab reinforcement
TECHNICAL SPECIFICATION - FLOOR AND ROOF BRACKETS
Figure 2
Chimney Stack
Flashing Ceiling Joist
min 400mm
50mm x 4mm Galv. steel
strap. Three M12 bolts at
75mm min ctrs
Packer each side
See NZBC acceptable solution
B1/AS3 Paragraph 1.7.2
Floor and Roof Brackets
Note:
Although drawn for roof restraint of a chimney on an exterior wall, the bracket details also apply to
an interior chimney and floor restraint of chimneys.TECHNICAL SPECIFICATION - CHIMNEY RESTRAINT
Figure 3
D12 grouted into
50mm Ø duct Flue
90mm
Fixing Tie
See Note 1
Fixing Bracket
See Note 2
Packer. See
NZBC B1/AS3
Fix Bracket to stud
Paragraph 1.7.2
with 12mm Ø
coach screw
50mm
Double Stud
Option A Option B
Notes: Notes:
1. Ties shall comprise 4mm galvanised hairpins located in 1. Brackets shall be made from 5mm thick M.S. angle with a
the mortar joints between units at no more than: 50mm hole drilled to suit the reinforcing duct. Locate brackets
in the mortar joints between units at no more than:
480mm maximum centres for stacks up to 600mm wide
320mm maximum centres for stacks over 600mm wide 480mm maximum centres for stacks up to 600mm wide
320mm maximum centres for stacks over 600mm wideTECHNICAL SPECIFICATION - STEEL REINFORCING DETAILS
Figure 4
Two outside stack
Base rods to be rods pass
bonded 200mm min continuously from
into gather with a high foundation to base
strength grout to gather to stack
A A
Two inside stack
rods to be fixed a
minimum of
200mm into gather
with a high
strength grout
Plan
50mm dia
ducts for
reinforcing
rods
Chimney stack units
D12 grouted in
50mm diameter duct
50mm dia duct for
reinforcing in gather
D12 in high strength
grout over length of
200mm min
gather
D12 grouted in
50mm diameter duct
Chimney base
Chimney Foundation
and starters as in Fig. 1
Section A-ATECHNICAL SPECIFICATION - BRICK VENEERS
Figure 5
Secured to wall (internal
or external) at no less than
intervals of 2.4 metres.
50mm x 4mm
U strap at
roof level
above roof level fixing
2.4m max cantilever
See Note
fix to ceiling
joist with
3 x M12 galv.
bolts @
A A 75mm min
centres
80 x 60 x 5mm M.S. angle
or 65 x 10mm M.S. flat Section A-A
Grouting
between Packer each side. See
chimney & brick NZBC acceptable solution
veneer shall be B1/AS3 Paragraph 1.7.2
17.5 mPa
50mm grouting cavity
Bricks shall
be fixed to
Max height 9m
precast
chimney with
brickweld
between the
joints.
Firebricks
D12 at 400mm
max ctrs Precast Pumice Units
(300mm min laps)
Brick Veneer
See Note
B B
Section B-B
Note:
Figure 5 has been drawn for the chimney being
exterior to the building
Vertical Section The dotted lines indicate the ceiling joists and floor for
an internal chimney.SUSTAINABILITY: THE FIRTH CONCRETE & CONCRETE MASONRY SUSTAINABILITY LIFECYCLE
n
4 Environmentally compliant manufacturing plants n
4 Most wash water returned from construction sites For more on Firth’s
n
4 Surplus water and some aggregates recycled n
4 Highly durable, low maintenance buildings and no rot contribution to building
n
4 Low transport impacts n
4 High degree of noise control a sustainable tomorrow
n
4 Leftover concrete returned from construction sites n
4 Inherent fire resistance today, visit www.firth.co.nz
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4 Passive solar heated thermal mass makes completed buildings n
4 Overall longer effective building life or call us on 0800 800 576
more energy-efficient n
4 Demolished concrete can be recycled as hard fill or aggregate for our free brochure.
© Copyright Firth 2010 Dec 2010 Chalis FIR21054
0800 800 576
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