prEN 13384-1

SLOVENSKI STANDARD
01-julij-2025
Dimniki - Računske metode termodinamike in dinamike fluidov - 1. del: Dimniki za
eno kurilno napravo
Chimneys - Thermal and fluid dynamic calculation methods - Part 1: Chimneys serving
one combustion appliance
Abgasanlagen - Wärme- und strömungstechnische Berechnungsverfahren - Teil 1:
Abgasanlagen mit einer Verbrennungseinrichtung
Conduits de fumée - Méthodes de calcul thermoaéraulique - Partie 1: Conduits de fumée
ne desservant qu'un seul appareil à combustion
Ta slovenski standard je istoveten z: prEN 13348-1
ICS:
91.060.40 Dimniki, jaški, kanali Chimneys, shafts, ducts
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
EUROPEAN STANDARD
prEN 13348-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
May 2025
ICS Will supersede EN 13384-1:2015+A1:2019
English Version
Chimneys - Thermal and fluid dynamic calculation
methods - Part 1: Chimneys serving one combustion
appliance
Conduits de fumée - Méthodes de calcul thermo- Abgasanlagen - Wärme- und strömungstechnische
aéraulique - Partie 1: Conduits de fumée ne desservant Berechnungsverfahren - Teil 1: Abgasanlagen mit einer
qu'un seul appareil à combustion Verbrennungseinrichtung
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 166.
If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations
which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC
Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are
aware and to provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 13348-1:2025 E
worldwide for CEN national Members.

Contents Page
European foreword . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Symbols and abbreviations .11
5 Calculation method for non-balanced flue chimneys .15
5.1 General principles .15
5.2 Pressure requirements .16
5.2.1 Negative pressure chimneys .16
5.2.2 Positive pressure chimneys .17
5.3 Temperature requirement .18
5.4 Calculation procedure .19
5.5 Flue gas data characterising the combustion appliance .19
5.5.1 General .19
5.5.2 Flue gas mass flow and combustion air mass flow .20
5.5.3 Flue gas temperature .21
5.5.4 Minimum draught for the combustion appliance (P ) for negative pressure
W
chimney .21
5.5.5 Maximum draught for the combustion appliance (P ) for negative pressure
Wmax
chimney .22
5.5.6 Maximum differential pressure of the combustion appliance (P ) for positive
WO
pressure chimney .22
5.5.7 Minimum differential pressure of the combustion appliance (P ) for positive
WOmin
pressure chimney .22
5.6 Characteristic data for the calculation .22
5.6.1 General .22
5.6.2 Mean value for roughness (r) .22
5.6.3 Thermal resistance (1/Λ) .22
5.7 Basic values for the calculation .23
5.7.1 Air temperatures .23
5.7.2 External air pressure (p ) .25
L
5.7.3 Gas constant .25
5.7.4 Density of the external air (ρ ).25
L
5.7.5 Specific heat capacity of the flue gas (c ) .26
p
5.7.6 Condensing temperature (T ) .26
sp
5.7.7 Correction factor for temperature instability (S ) .26
H
5.7.8 Flow safety coefficients (S and S ) .26
E EB
5.8 Determination of the temperatures .26
5.8.1 General .26
5.8.2 Calculation of the coefficient of cooling (K) .27
5.8.3 Coefficient of heat transmission (k ) .27
b
5.9 Determination of the density of the flue gas and the velocity of the flue gas .29
5.9.1 Density of the flue gas (ρ ) .29
m
5.9.2 Velocity of the flue gas (w ) .30
m
5.10 Determination of the pressures . 30
5.10.1 Pressure at the flue gas inlet into the chimney . 30
5.10.2 Theoretical draught available due to chimney effect (P ) . 31
H
5.10.3 Pressure resistance of the chimney (P ) . 31
R
5.10.4 Wind velocity pressure (P ) . 33
L
5.11 Minimum draught required at the flue gas inlet into the chimney and maximum
allowed draught (P and P ) and maximum and minimum differential pressure
Ze Zemax
at the flue gas inlet into the chimney (P and P ) . 33
ZOe ZOemin
5.11.1 General . 33
5.11.2 Minimum and maximum draught for the combustion appliance (P and P ) and
W Wmax
maximum and minimum differential pressure of the combustion appliance (P
WO
and P ) . 34
WOmin
5.11.3 Effective pressure resistance of the connecting flue pipe (P ) . 34
FV
5.11.4 Pressure resistance of the air supply (P ) . 36
B
5.12 Calculation of the inner surface temperature at the chimney outlet (T ) . 37
iob
6 Secondary air for negative pressure chimneys . 38
6.1 General . 38
6.2 Calculation method . 39
6.3 Basic values for the calculation of secondary air . 39
6.3.1 General . 39
6.3.2 Mixing calculations . 39
6.4 Pressures . 40
6.4.1 Pressure resistance for the air supply with secondary air (P ) . 40
BNL
6.4.2 Draught required for the secondary air devices (P ) . 42
NL
6.4.3 Pressure resistance for that part of the connecting flue pipe before the secondary
air device (P ) . 43
FV1
6.4.4 Pressure requirement with secondary air . 43
6.5 Temperature requirement with secondary air . 43
7 Calculation method for balanced flue chimneys . 43
7.1 General principles . 43
7.2 Pressure requirements . 44
7.3 Temperature requirements . 45
7.4 Calculation procedure . 45
7.5 Flue gas data characterizing the combustion appliance . 46
7.6 Characteristic data for the calculation . 46
7.7 Basic values for the calculation . 46
7.7.1 Air temperatures . 46
7.7.2 Other basic values . 47
7.8 Determination of the temperatures . 47
7.8.1 Non-concentric (separate) ducts. 47
7.8.2 Concentric ducts . 47
7.8.3 Mean temperatures for pressure calculation . 62
7.9 Determination of densities and velocities . 63
7.9.1 Density and velocity of the flue gas . 63
7.9.2 Density and velocity of the combustion air . 63
7.10 Determination of pressures . 65
7.10.1 Pressures in the flue duct and the connecting flue pipe . 65
7.10.2 Pressures in the air supply duct and the connecting air supply pipe . 65
7.11 Calculation of the inner surface temperature at the flue duct outlet (T ) . 68
iob
8 Consideration of the condensation heat of the flue gas water vapour . 69
8.1 General . 69
8.2 Onset of condensation . 70
8.3 Calculation of the flue gas temperature at the outlet of a chimney segment with
condensation (j ≥ NsegK) .72
9 Consideration of chimney fans .77
9.1 General .77
9.2 Inline fans .78
9.3 Exhaust fans .79
Annex A (informative) Calculation of thermal resistance .80
Annex B (informative) Default values for non-available product information .81
Annex C (informative) Chimney outlet with regard to adjacent buildings . 100
Annex D (informative) Determination of the gas constant R considering the condensation
.............................................................................................................................................................. 101
Annex E (informative) Example for a report about input and output data of the calculation
.............................................................................................................................................................. 102
Bibliography. 111
European foreword
This document (prEN 13384-1:2025) has been prepared by Technical Committee CEN/TC 166
“Chimneys”, the secretariat of which is held by ASI.
This document is currently submitted to the CEN Enquiry.
This document will supersede EN 13384-1:2015+A1:2019.
In comparison to EN 13384-1-2015+A1:2019 the following technical changes are given:
— editorial mistakes have been corrected;
— in Table B.1 new fuels have been added;
— a clarification is made for the ζ-values of terminals, linked to static pressure;
— the calculation methods were extended to include the O content of the flue gas;
— for concentric duct the simplified heat transfer calculation method based on S has been deleted.
rad
Therefore, the detailed calculation method has been modified;
— the pressure requirements for negative pressure chimneys have been modified for a possible
connection of a positive pressure combustion appliance with a total or partly positive pressure
connection pipe;
— remarks are added for the temperature requirement;
— introduction of a new mass flow factor for on all sides open fire places;
— introduction of a new formula for calculation of thermal resistance of the air gap;
— remarks are added for calculation of draught regulators for balanced flue chimneys;
— a new Annex E “Example for a report about input and output data of the calculation” has been
created.
This document has been prepared under a mandate given to CEN by the European Commission and the
European Free Trade Association.
EN 13384, “Chimneys — Thermal and fluid dynamic calculation methods” consists of three Parts:
— Part 1: Chimneys serving one combustion appliance
— Part 2: Chimneys serving more than one combustion appliance
— Part 3: Methods for the development of diagrams and tables for chimneys serving one heating
appliance
1 Scope
This document specifies methods for the calculation of the thermal and fluid dynamic characteristics of
chimneys serving one combustion appliance.
The methods in this part of this document are applicable to negative or positive pressure chimneys with
wet or dry operating conditions. It is valid for chimneys with combustion appliances for fuels subject to
the knowledge of the flue gas characteristics which are needed for the calculation.
The methods in this part of this document are applicable to chimneys with one inlet connected with one
combustion appliance.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
EN 1443:2019, Chimneys - General requirements
EN 1749, Classification of gas appliances according to the method of supplying combustion air and of
evacuation of the combustion products (types)
EN 15287-1:2023, Chimneys - Design, installation and commissioning - Part 1: Chimneys and connecting
flue pipes for non-roomsealed combustion appliances
EN 15287-2:2023, Chimneys - Design, installation and commissioning - Part 2: Chimneys and connecting
flue pipes for roomsealed combustion appliances
EN 16475-2:—, Chimneys - Accessories - Part 2: Chimney fans - Requirements and test methods
EN 16475-3:—, Chimneys - Accessories - Part 3: Draught regulators, standstill opening devices and
combined secondary air devices - Requirements and test methods
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 1443:2019, EN 15287-1:2023,
EN 15287-2:2023 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
heat output
Q
amount of heat produced by a combustion appliance per unit of time

Under preparation. Stage at time of publication: prEN 16475-2:2025
Under preparation. Stage at time of publication: prEN 16475-3:2025
3.1.1
nominal heat output
Q
N
continuous heat output specified in the documentation of the combustion appliance related to specified
fuels
3.1.2
heat output range
range of output below the nominal heat output specified in the documentation over which the
combustion appliance can be used
3.2
heat input
Q
F
amount of heat in unit time which is supplied to the combustion appliance by the fuel based on its net
caloric value H
u
3.3
efficiency of the combustion appliance

ηW
ratio of the heat output (Q) from the combustion appliance to the heat input (Q )
F
3.4
flue gas mass flow
𝒎𝒎̇
mass of flue gas leaving the combustion appliance through the connecting flue pipe per time unit
3.5
effective height of the chimney
H
difference in height between the axis of the flue gas inlet into the chimney and the outlet of the chimney
3.6
effective height of the connecting flue pipe
H
V
difference in height between the axis of the flue gas chimney outlet of the combustion appliance and the
axis of the flue gas inlet into the chimney
Note 1 to entry In the case of open fire chimneys, H is the difference in height between the height of the
V
upper frame of the furnace and the axis of the flue gas inlet into the chimney.
3.7
draught
positive value of the negative pressure in the flue
3.8
theoretical draught available due to chimney effect
P
H
pressure difference caused by the difference in weight between the column of air equal to the effective
height outside a chimney and the column of flue gas equal to the effective height inside the chimney
3.9
pressure resistance of the chimney
P
R
pressure which is necessary to overcome the resistance of the flue gas mass flow which exists when
carrying the flue gases through the chimney
3.10
wind velocity pressure
P
L
pressure generated on the chimney due to wind
3.11
minimum draught at the flue gas inlet into the chimney
P
Z
difference between the minimum theoretical draught and the sum of the maximum pressure resistance
of the chimney and the wind velocity pressure
3.12
maximum draught at the flue gas inlet into the chimney

PZmax
difference between the maximum theoretical draught and the minimum pressure resistance in the
chimney
3.13
minimum draught for the combustion appliance
P
W
difference between the static air pressure of the room of installation of the combustion appliance and
the static pressure of the flue gas at the chimney outlet of the combustion appliance which is necessary
to maintain the correct operation of the combustion appliance
3.14
maximum draught for the combustion appliance
P
Wmax
difference between the static air pressure of the room of installation of the combustion appliance and
the static pressure of the flue gas at the outlet of the combustion appliance which is the maximum
allowed to maintain the correct operation of the combustion appliance
3.15
effective pressure resistance of the connecting flue pipe
P
FV
static pressure difference between the axis of the inlet of the connecting flue pipe and the axis of the
chimney outlet due to the theoretical draught and pressure resistance
3.16
effective pressure resistance of the air supply
P
B
difference between the static pressure in the open air and the static air pressure in the room of
installation of the combustion appliance at the same height
3.17
minimum draught required at the flue gas inlet into the chimney
P
Ze
sum of the minimum draught required for the combustion appliance and the draught required to
overcome the effective pressure resistance of the connecting flue pipe and the effective pressure
resistance of the air supply
3.18
maximum allowed draught at the flue gas inlet into the chimney
P
Zemax
sum of the maximum draught allowed for the combustion appliance and the draught required to
overcome the effective pressure resistance of the connecting flue pipe and the effective pressure
resistance of the air supply
3.19
maximum positive pressure at the flue gas inlet into the chimney
P
ZO
difference of the maximum pressure resistance and the minimum theoretical draught of the chimney
added by the wind velocity pressure
3.20
minimum positive pressure at the flue gas inlet into the chimney
P
ZOmin
difference of the minimum pressure resistance and the maximum theoretical draught of the chimney
3.21
maximum differential pressure of the combustion appliance
P
WO
maximum difference between the static pressure of the flue gas at the chimney outlet of the combustion
appliance and the static pressure of the air at the inlet to the combustion appliance specified for its
correct operation
3.22
minimum differential pressure of the combustion appliance
P
WOmin
minimum difference between the static pressure of the flue gas at the outlet of the combustion appliance
and the static pressure of the air at the inlet to the combustion appliance specified for its correct
operation. This can be a negative value.
3.23
maximum differential pressure at the flue gas inlet into the chimney
PZOe
difference between the maximum differential pressure of the combustion appliance and the sum of the
effective pressure resistance of the connecting flue pipe and the effective pressure resistance of the air
supply
3.24
secondary air
ambient air added to the flue gas in addition to the nominal flue gas mass flow
3.25
minimum differential pressure at the flue gas inlet into the chimney
P
ZOemin
difference between the minimum differential pressure of the combustion appliance and the sum of the
effective pressure resistance of the connecting flue pipe and the effective pressure resistance of the air
supply
3.26
secondary air device
draught regulator or a draught diverter
3.27
draught regulator
component which automatically supplies ambient air to the chimney, the connecting flue pipe or the
combustion appliance
3.28
draught diverter
device, placed in the combustion products passage of the combustion appliance, that is intended to
maintain the quality of combustion within certain limits and to keep the combustion stable under certain
conditions of up draught and down draught
3.29
temperature limit of the inner surface
T
g
allowed minimum temperature of the inner surface of the chimney outlet
3.30
air-supply duct
component or components parallel to the chimney (separate or concentric) that conveys combustion
air from the outside atmosphere to the inlet of the connecting air supply pipe
3.31
balanced flue chimney
chimney where the point of air entry to the air supply duct is adjacent to the point of discharge of
combustion products from the flue, the inlet and outlet being so positioned that wind effects are
substantially balanced
3.32
chimney segment
calculation part of a chimney
3.33
condensate mass flow
𝜟𝜟𝒎𝒎̇
𝐃𝐃
mass of water vapour of the flue gas condensed in the combustion appliance, connecting flue pipe or the
chimney per time unit
3.34
connecting air supply pipe
component or components connecting the air supply duct outlet with the room-sealed combustion
appliance combustion air inlet
3.35
condensation factor
f
K
proportion of the theoretical maximum condensation mass flow usable in the calculation
3.36
chimney fan
exhaust fan or inline fan
3.36.1
exhaust fan
fan positioned on the outlet of the chimney
3.36.2
inline fan
fan positioned as a section of the connecting flue
4 Symbols and abbreviations
The symbols given in this clause can be completed by one or more indices to indicate location or
materials if necessary.
Table 1 — Symbols, terminology and units
Symbol Terminology Unit
A cross sectional area m
c specific heat capacity J/(kg · K)
c specific heat capacity of flue gas J/(kg · K)
p
d thickness of the section m
D diameter m
D hydraulic diameter
m
h
E heat flux ratio –
g acceleration due to gravity m/s
H effective height of the chimney m
k coefficient for heat transmission W/(m · K)
K coefficient of cooling –
L length m
l proportion of condensation surface –
C
𝑚𝑚̇ flue gas mass flow kg/s
flue gas mass flow of combustion appliance reduced by condensed
𝑚𝑚̇ kg/s
𝑊𝑊
water
𝑚𝑚̇ condensate mass flow kg/s
𝐷𝐷
N Nusselt number –
u
Symbol Terminology Unit
N number of segments –
seg
p static pressure Pa
p external air pressure Pa
L
P effective pressure resistance of the air supply Pa
B
P pressure resistance due to friction and form resistance of the chimney Pa
E
P effective pressure resistance of the connecting flue pipe Pa
FV
difference in pressure caused by change of velocity of flue gas in the
P Pa
G
chimney
P theoretical draught available due to chimney effect Pa
H
theoretical draught available due to chimney effect of the connecting
P Pa
HV
flue pipe
P wind velocity pressure Pa
L
P draught required for secondary air devices Pa
NL
P pressure resistance of the chimney Pa
R
P pressure resistance of the connecting flue pipe Pa
RV
P minimum draught for the combustion appliance Pa
W
P maximum draught for the combustion appliance Pa
Wmax
P maximum differential pressure of the combustion appliance Pa
WO
P minimum differential pressure of the combustion appliance Pa
WOmin
P minimum draught at the flue gas inlet into the chimney Pa
Z
P maximum draught at the flue gas inlet into the chimney Pa
Zmax
P minimum draught required at the flue gas inlet into the chimney Pa
Ze
P maximum allowed draught at the flue gas inlet into the chimney Pa
Zemax
P maximum positive pressure at the flue gas inlet into the chimney Pa
ZO
P minimum positive pressure at the flue gas inlet into the chimney Pa
ZOmin
P maximum differential pressure at the flue gas inlet into the chimney Pa
ZOe
P minimum differential pressure at the flue gas inlet into the chimney Pa
ZOemin
P maximum allowed pressure from the designation of the chimney Pa
Zexcess
maximum allowed pressure from the designation of the connecting flue
P Pa
ZVexcess
pipe
Pr Prandtl number –
q heat transfer from the flue to the outer surface W
C
q condensation heat W
K
Q heat output kW
Q heat input kW
F
Symbol Terminology Unit
Q nominal heat output kW
N
r mean value for roughness of the inner surface m
R gas constant of the flue gas J/(kg · K)
R gas constant of the air J/(kg · K)
L
Re Reynolds number –
s cross section m
SE flow safety coefficient –
S correction factor for temperature instability –
H
t temperature °C
T temperature, absolute K
T flue gas temperature at the chimney inlet K
e
T temperature limit K
g
T inner surface temperature at chimney outlet K
io
inner surface temperature at the chimney outlet at temperature
T K
iob
equilibrium
T flue gas temperature immediately before the additional insulation K
irb
T external air temperature K
L
T mean temperature of the flue gas K
m
T flue gas temperature at the chimney outlet K
o
T water dew point K
p
T condensing temperature K
sp
T ambient air temperature K
u
T ambient air temperature of the boiler room K
ub
T ambient air temperature for heated areas K
uh
T ambient air temperature for areas external to the building K
ul
T ambient air temperature at the chimney outlet K
uo
the ambient air temperature immediately before the additional
T K
ur
insulation
T ambient air temperature for unheated areas inside the house K
uu
T flue gas temperature of the combustion appliance K
W
flue gas temperature of the combustion appliance at nominal heat
T K
WN
output
flue gas temperature of the combustion appliance at the lowest possible
T K
Wmin
heat output
Symbol Terminology Unit
U internal chimney segment parameter m
w mean velocity within a cross section m/s
w mean velocity over a defined length m/s
m
y form value –
z height above sea level m
α coefficient of heat transfer W/(m · K)
β ratio of the combustion air mass flow to the flue gas mass flow –
γ angle between flow directions °
δ wall thickness m
ε proportion of black body radiation emitted by a surface –
coefficient of flow resistance due to a directional and/or
ζ –
cross sectional and/or mass flow change in the flue
dynamic viscosity
η
N ⋅ s/m
η efficiency of the combustion appliance –
W
η efficiency of the combustion appliance at nominal heat output –
WN
λ coefficient of thermal conductivity W/(m · K)
ρ density kg/m
ρ density of the external air
kg/m
L
mean density of flue gas averaged over a defined length and over the
ρ kg/m
m
cross section
σ(CO ) volume-concentration of CO %
2 2
σ(O ) volume-concentration of O %
2 2
σ(H O) volume-concentration of H O (vapour) %
2 2
2 4
σ black body radiation number W/(m · K )
rad
ψ coefficient of flow resistance due to friction of the flue –
thermal resistance
m · K/W
� �
𝛬𝛬
Table 2 — Additional subscripts
Subscript Terminology Unit
a outside –
A flue gas –
b equilibrium temperature condition –
B combustion air –
D water vapour –
e inlet –
F open fire place –
G change in velocity –
i inside –
K condensation –
L open air (outside) –
m mean value –
M mixture –
n counting index –
N nominal value –
NL secondary air –
o chimney outlet –
O positive pressure –
tot totalized over all sections (segments) –
u ambient air –
V connecting flue pipe –
W combustion appliance –
5 Calculation method for non-balanced flue chimneys
5.1 General principles
The calculation of inside dimensions (cross section) of negative pressure chimneys is based on the
following four criteria:
— the minimum draught at the flue gas inlet into the chimney shall be equal to or greater than the
minimum draught required at the flue gas inlet into the chimney;
— the minimum draught at the flue gas inlet to the chimney shall be equal to or greater than the
effective pressure resistance of the air supply;
— the maximum draught at the flue gas inlet into the chimney shall be equal to or less than the
maximum allowed draught at the flue gas inlet into the chimney;
— the temperature of the inner surface at the outlet of the chimney shall be equal to or greater than
the temperature limit.
The calculation of inside dimensions (cross section) of positive pressure is based on the following four
criteria:
— the maximum positive pressure at the flue gas inlet into the chimney shall be equal or less than the
maximum differential pressure at the flue gas inlet into the chimney;
— the maximum positive pressure in the connecting flue pipe and in the chimney shall not be higher
than the excess pressure for which both are designated;
— the minimum positive pressure at the flue gas inlet into the chimney shall be equal or greater than
the minimum differential pressure at the flue gas inlet into the chimney;
— the temperature of the inner surface at the chimney outlet of the chimney shall be equal to greater
than the temperature limit.
NOTE The pressure requirements for maximum draught or minimum positive pressure are only required if
there is a limit for the maximum draught for the negative pressure combustion appliance or a minimum differential
pressure of the positive pressure combustion appliance.
In order to verify the criteria two sets of external conditions are used:
— the calculation of the minimum draught and maximum positive pressure is made with conditions
for which the capacity of the chimney is minimal (i.e. high outside temperature); and also
— the calculation of the maximum draught and minimum positive pressure and of the inner surface
temperature with conditions for which the inside temperature of the chimney is minimal (i.e. low
outside temperature.
The input data and results of the calculation shall be reported. An example of the content is given in
Annex E.
5.2 Pressure requirements
5.2.1 Negative pressure chimneys
The following relationships shall be verified:
P = P − P − P ≥ P + P + P = P , in Pa (1)
Z H R L W FV B Ze
P ≥ P , in Pa (2)
Z B
and if P < 0 Pa and the connecting flue pipe is designated for negative pressure (N):
W
P ≥ P + P , in Pa (3)
Z B FV
or if P < 0 Pa and the connecting flue pipe is designated for positive pressure (P, M or H):
W
P – P ≤ P , in Pa (4)
FV Z ZVexcess
or if P < 0 Pa and only the first part of the connecting flue pipe is designated for positive pressure:
W
P ≥ P + P , in Pa (5)
Z B FV2
P + P – P ≤ P , in Pa (6)
FV1 FV2 Z ZVexcess
and if appropriate
P = P − P ≤ P + P + P = P , in Pa (7)
Zmax H R Wmax FV B Zemax
where
P is the effective pressure resistance of air supply (see 5.11.3), in Pa;
B
P is the effective pressure resistance of the connecting flue pipe, in Pa;
FV
P is the effective pressure resistance of a first, positive pressure part of the connecting flue
FV1
pipe, in Pa;
P is the effective pressure resistance of a second, negative pressure part of the connecting
FV2
flue pipe, in Pa;
P is the theoretical draught available due to chimney effect, in Pa;
H
P is the wind velocity pressure, in Pa;
L
P is the pressure resistance of the chimney, in Pa;
R
P is the minimum draught for the combustion appliance, in Pa;
W
P is the maximum draught for the combustion appliance, in Pa;
Wmax
P is the minimum draught at the flue gas inlet into the chimney (see 5.10), in Pa;
Z
P is the maximum draught at the flue gas inlet into the chimney (see 5.11), in Pa;
Zmax
P is the minimum draught required at the flue gas inlet into the chimney, in Pa;
Ze
P is the maximum allowed draught at the flue gas inlet into the chimney, in Pa.
Zemax
P is the maximum allowed pressure from the designation of the connecting flue pipe, in Pa.
ZVexcess
NOTE The values of PH and PR in Formulas (1) and (7) are normally different because the conditions are
different.
5.2.2 Positive pressure chimneys
The following relationships shall be verified:
P = P - P + P ≤ P - P - P = P , in Pa (8)
ZO R H L WO B FV Zoe
P ≤ P , in Pa (9)
ZO Z excess
P + P ≤ P , in Pa (10)
ZO FV ZV excess
and if appropiate
P = P - P ≥ P - P - P = P , in Pa (11)
ZOmin R H WOmin B FV Zoemin
where
P is the effective pressure resistance of air supply, in Pa;
B
P is the effective pressure resistance of the connecting flue pipe, in Pa;
FV
P is the theoretical draught available due to chimney effect, in Pa;
H
P is the wind velocity pressure, in Pa;
L
P is the pressure resistance of the chimney, in Pa;
R
P is the maximum differential pressure of the combustion appliance, in Pa;
WO
P is the minimum differential pressure of the combustion appliance, in Pa;
WOmin
P is the maximum positive pressure at the flue gas inlet into the chimney, in Pa;
ZO
P is the minimum positive pressure at the flue gas inlet into the chimney, in Pa;
ZOmin
P is the maximum differential pressure at the flue gas inlet into the chimney, in Pa;
ZOe
P is the minimum differential pressure at the flue gas inlet into the chimney, in Pa;
ZOemin
P is the maximum allowed pressure from the designation of the chimney, in Pa;
Z excess
P is the maximum allowed pressure from the designation of the connecting flue pipe, in Pa.
ZVexcess
NOTE The values of P and P in Formulas (8) and (11) are normally different because the conditions are
H R
different
5.3 Temperature requirement
The following relationship shall be verified:
𝑇𝑇 ≥𝑇𝑇 , in K (12)
iob 𝑔𝑔
where
T is the inner surface temperature at the chimney outlet at temperature
iob
equilibrium, in K;
T is the temperature limit, in K.
ig
If the chimney above the roof has additional insulation the following relationship shall also be verified:
𝑇𝑇 ≥𝑇𝑇 , in K (13)
irb 𝑔𝑔
where
T is the inner surface temperature immediately before the additional insulation,
irb
in K.
The temperature limit T of chimneys with dry operating conditions shall be taken as the condensing
ig
temperature T of the flue gas (see 5.7.6).
sp
The temperature limits T of chimneys with wet operating conditions shall be taken as 273,15 K which
ig
prevents the formation of ice at the chimney outlet.
NOTE The comparison of the inner surface temperature before the additional insulation T with the
iirb
admissible limit temperature of the flue gas T is not necessary, if the value of the thermal resistance of the
ig
additional insulation is not more than 0,1 (m ⋅ K)/W. For chimneys operating under wet conditions the
comparison is not necessary, if the value of the ambient air temperature immediately before the additional
insulation is ≥ 0 °C.
Particularly when replacing a combustion appliance on an existing chimney, compliance with the
temperature condition can be waived in speci�ic individual cases if the �ire and operational safety of
the system is not restricted. This can be assumed e.g. if at least one of the following conditions is met:
- After replacing a non-condensing combustion appliance by a similar kind of combustion appliance
on an existing chimney for dry operation conditions, there is a risk of moistering if no adjustment of
the
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