kSIST FprEN 15544:2022

One off Kachelgrundöfen/Putzgrundöfen (tiled/mortared stoves) - Dimensioning

This standard specifies calculations for the dimensioning of Kachelgrundöfen/Putzgrundöfen (tiled/mortared stoves) based upon the required nominal heat output of the stove as declared by the producer. The Kachelgrundöfen/Putzgrundöfen (tiled/mortared stoves) are of individual one-off construction design. The standard can be used for log wood fired Kachelöfen (tile stoves) that burn one fuel load per storage period with a maximum load between 10 kg and 40 kg and a storage period (nominal heating time) between 8 h and 24 h.
This standard is valid for Kachelgrundöfen/Putzgrundöfen (tiled/mortared stoves) equipped with fireclay as interior material, with an apparent density between 1,750 kg/m³ and 2,200 kg/m³, a degree of porosity from 18 % up to 33 % by volume and a heat conductivity from 0,65 W/mK up to 0,90 W/mK (temperature range 20 °C to 400 °C).
This standard is valid for Kachelgrundöfen/Putzgrundöfen (tiled/mortared stoves) with sidewise combustion air supply of the combustion chamber and an inflow speed from 2 m/s to 4 m/s, whereas the height of the lowest opening is at least 5 cm above the bottom of the combustion chamber.
This standard is not valid for combinations with water heat exchangers for central heating or other heat absorbing elements like glass plates greater than 1/6 of the combustion chamber surface, open water tanks, etc. It is also not valid for combinations with heating/fireplace elements according to EN 13229. Furthermore this standard is not valid for mass-produced prefabricated or partly prefabricated slow heat release appliances according to EN 15250.
NOTE   Although for the purposes of this standard these calculations are applicable only to the requirements of this standard, the same calculations can be used for other purposes, e.g. to verify emission levels and energy efficiency in case of burning log wood or wood briquettes according to the producer’s manual.

Ortsfest gesetzte Kachelgrundöfen/Putzgrundöfen - Auslegung

Die Anwendung der Berechnungen dieses Dokuments dient zum Nachweis der Emissionswerte von Kohlenstoffmonoxid, Stickstoffdioxid, organisch gebundenem Kohlenstoff sowie von Staub und des Wirkungsgrades.
Werden die Berechnungen dieses Dokuments eingehalten, so werden zumindest Emissionswerte von Kohlenstoffmonoxid 1 500 mg/mn3 (1 000 mg/MJ), Stickstoffdioxid 225 mg/mn3 (150 mg/MJ), organisch gebundenem Kohlenstoff 120 mg/mn3 (80 mg/MJ) sowie Staub 90 mg/mn3 (60 mg/MJ) eingehalten. Werden die Berechnungen dieses Dokuments in Kombination mit geeigneten Brennräumen angewendet, welche die Einhaltung niedrigerer Emissionswerte im Rahmen einer Typprüfung nachweisen, so werden auch diese Werte als eingehalten angesehen.
Es kann nationale oder lokale Regulierungen geben, die strengere Emissions- und Effizienzanforderungen festlegen.
Dieses Dokument enthält Festlegungen für die Bemessung von Kachelgrundöfen/Putzgrundöfen auf Basis der erforderlichen Nennwärmeleistung, wie sie vom Hersteller angegeben wurde. Dabei handelt es sich um handwerklich individuell gesetzte Kachelgrundöfen/Putzgrundöfenöfen. Dieses Dokument ist auf Scheitholz befeuerte Kachelöfen mit einmaliger Brennstoffauflage je Speicherdauer mit maximalen Brennstoffmassen zwischen 10 kg und 40 kg (Scheitholz mit Wassergehalt von 12 % bis 20 %, Durchmesser bzw. Dicke der Scheite von 5 cm bis 10 cm, Länge der Scheite von 25 cm bis 50 cm orientiert an den Brennraumabmessungen) und einer Speicherdauer (Nennheizzeit) von 8 h bis 24 h anzuwenden.
Dieses Dokument gilt für Kachelgrundöfen/Putzgrundöfen mit dem Ausbaustoff Schamotte mit einer Rohdichte zwischen 1 750 kg/m3 und 2 300 kg/m3, einer offenen Porosität von 17 Vol. % bis 33 Vol. % sowie einer Wärmeleitfähigkeit im Temperaturbereich von 20 °C bis 400 °C zwischen 0,90 W/mK und 1,35 W/mK.
Dieses Dokument gilt für Kachelgrundöfen/Putzgrundöfen mit Verbrennungsluftzufuhr von der Seite über eine Türzarge oder einen Stehrost der Heiztüre in den Brennraum. Dieses Dokument gilt für eine Einlassgeschwindigkeit der Verbrennungsluft zwischen 2 m/s bis 4 m/s.
Dieses Dokument gilt außerdem für die Kombination mit Brennräumen, die für handwerklich ortsfest gesetzte Kachelgrundöfen/Putzgrundöfen geeignet sind und für die die Einhaltung der gesetzlich geforderten Emissionswerte im Rahmen einer Typprüfung durch eine akkreditierte und/oder notifiziert Stelle nachgewiesen wurde.
Dieses Dokument gilt für Brennräume:
-   mit einer Luftzahl zwischen 1,95 und 3,95 nach Typprüfung;
-   mit einer maximalen Brennstoffmasse von 5 kg bis 40 kg;
-   Verwendung anderer geeigneter Materialien sowie Schamotte.
Hinsichtlich der Typprüfung gilt dieses Dokument für Brennräume, die geprüft sind:
-   nach EN 15250 (oder prEN 16510-2-5);
-   nach EN 13229 (oder prEN 16510-2-2); oder
-   nach entsprechenden nationalen Normen (z.B. ÖNORM B 8303).
Dieses Dokument gilt für Brennräume, welche für die chargenweise Verbrennung von Pellets ausgelegt sind, wenn die Anforderungen nach diesem Dokument erfüllt sind (Luftzahl von 1,95 bis 3,95, Abbranddauer von (78 ± 20) min).
Dieses Dokument gilt nicht für:
-   Kombinationen mit Wasserwärmetauschern für Zentralheizungen oder anderen Wärme entziehende Einbauten, wie Wasserschiffen;
-   Brennräume mit Glasscheiben größer als 1/5 der Brennraum-Innenfläche;
-   in Serie vorgefertigte Speichereinzelfeuerstätten bzw. teilvorgefertigte Speichereinzelfeuerstätten nach EN 15250 (oder prEN 16510-2-5).

Poêles en faïence, poêles en maçonnerie fabriqués in situ - Dimensionnement

L’application des calculs du présent document permet de vérifier les valeurs d’émission de monoxyde de carbone, de dioxyde d’azote, de carbone organique ainsi que de poussière et le rendement énergétique.
Le respect des calculs de ce document conduit à des valeurs d'émission inférieures ou égales à 1 500 mg/mn3 (1 000 mg/MJ) pour le monoxyde de carbone, à 225 mg/mn3 (150 mg/MJ) pour le dioxyde d'azote, à 120 mg/mn3 (80 mg/MJ) pour le carbone organique et à 90 mg/mn3 (60 mg/MJ) pour la poussière. Si les calculs de ce document sont utilisés en combinaison avec des chambres de combustion appropriées dont les valeurs d'émission s'avèrent inférieures lors d'un essai de type, ces valeurs sont également considérées comme respectées.
Certains règlements nationaux ou locaux peuvent imposer des exigences plus strictes en matière d’émissions et/ou de rendement.
Le présent document spécifie des calculs pour le dimensionnement des poêles en faïence et des poêles en maçonnerie fondés sur la puissance calorifique nominale requise du poêle telle que déclarée par le fabricant. Les poêles en faïence et les poêles en maçonnerie fabriqués in situ sont conçus sous forme de construction artisanale. Le présent document peut être utilisé pour des poêles en faïence et des poêles en maçonnerie à bûches de bois qui brûlent une charge de combustible par période d’accumulation avec une charge maximale comprise entre 10 kg et 40 kg (bûche de bois ayant une teneur en eau comprise entre 12 % et 20 %, un diamètre compris entre 5 cm à 10 cm, une longueur variant habituellement entre 25 cm et 50 cm, et basée sur les dimensions de la chambre de combustion) et une période d’accumulation (temps de chauffage nominal) comprise entre 8 h et 24 h.
Le présent document s’applique aux poêles en faïence et aux poêles en maçonnerie dont le matériau intérieur est de la brique réfractaire de masse volumique apparente comprise entre 1 750 kg/m3 et 2 300 kg/m3, d’un degré de porosité compris entre 17 % et 33 % en volume et d’une conductivité thermique comprise entre 0,90 W/mK et 1,35 W/mK (plage de température de 20 °C à 400 °C).
Le présent document s’applique aux poêles en faïence et aux poêles en maçonnerie dotés d’une alimentation en air de combustion latérale pour entrer dans la chambre de combustion via un cadre de porte de chargement ou la grille de la porte de chauffage. Le présent document s’applique pour une vitesse d’afflux d’air de combustion comprise entre 2 m/s et 4 m/s.
Le présent document s'applique également à la combinaison avec des chambres de combustion qui conviennent à des poêles en faïence et à des poêles en maçonnerie fabriqués in situ et pour lesquels la conformité aux valeurs d'émission légalement requises a été vérifiée dans le cadre d'un essai de type effectué par un organisme accrédité et/ou notifié.
Les conditions générales suivantes s’appliquent aux chambres de combustion :
-   présentant un rapport air-combustible compris entre 1,95 et 3,95, conformément à l’essai de type ;
-   présentant une charge maximale de 5 kg à 40 kg ;
-   utilisant d’autres matériaux aussi appropriés que la brique réfractaire.
Concernant l’essai de type, le présent document est applicable à des chambres de combustion qui sont soumises à essai :
-   conformément à l’EN 15250 (ou prEN 16510-2-5) ;
-   conformément à l’EN 13229 (ou prEN 16510-2-2) ; ou
-   conformément aux normes nationales respectives (par ex. ÖNORM B 8303).
Le présent document s’applique aux chambres de combustion ayant été soumises à un essai de type, conçues pour la combustion de granulés par lots si ceux-ci répondent aux exigences du présent document (rapport air-combustible compris entre 1,95 et 3,95, charge de granulés brûlée en 78 ± 20 minutes).
Le présent document ne s’applique pas dans les cas suivants :
...

Lončene peči - Dimenzioniranje

General Information

• Status: Not Published
• Public Enquiry End Date: 02-Nov-2021
• ICS: 97.100.30 - Solid fuel heaters
• Technical Committee: OGS - Heating for buildings
• Current Stage: 5020 - Formal vote (FV) (Adopted Project)
• Start Date: 13-Oct-2022
• Due Date: 01-Dec-2022
• Completion Date: 17-Oct-2022
• Ref Project: EN 15544:2023 - One off Kachelgrundöfen/Putzgrundöfen (tiled/mortared stoves) - Dimensioning

Relations

• Revised: SIST EN 15544:2009 - One off Kachelgrundöfen/Putzgrundöfen (tiled/mortared stoves) - Dimensioning
• Effective Date: 01-Oct-2021
• Revised: SIST EN 15544:2009 - One off Kachelgrundöfen/Putzgrundöfen (tiled/mortared stoves) - Dimensioning
• Effective Date: 18-Jan-2023

Standards Content (Sample)

SLOVENSKI STANDARD
oSIST prEN 15544:2021
01-oktober-2021
Lončene peči - Dimenzioniranje
One off Kachelgrundöfen/Putzgrundöfen (tiled/mortared stoves) - Dimensioning
Ortsfest gesetzte Kachelgrundöfen/Putzgrundöfen - Auslegung
Poêles en faïence, poêles en maçonnerie fabriqués in situ - Dimensionnement
Ta slovenski standard je istoveten z: prEN 15544
ICS:
97.100.30 Grelniki na trdo gorivo Solid fuel heaters
oSIST prEN 15544:2021 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN 15544:2021
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oSIST prEN 15544:2021
DRAFT
EUROPEAN STANDARD
prEN 15544
NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2021
ICS 97.100.30 Will supersede EN 15544:2009
English Version
One off Kachelgrundöfen/Putzgrundöfen (tiled/mortared
stoves) - Dimensioning

Poêles en faïence, poêles en maçonnerie fabriqués in Ortsfest gesetzte Kachelgrundöfen/Putzgrundöfen -

situ - Dimensionnement Auslegung

This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee

CEN/TC 295.

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, Turkey 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

© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 15544:2021 E

worldwide for CEN national Members.
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oSIST prEN 15544:2021
prEN 15544:2021 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

Introduction .................................................................................................................................................................... 4

1 Scope .................................................................................................................................................................... 5

2 Normative references .................................................................................................................................... 6

3 Terms and definitions ................................................................................................................................... 6

4 Calculations ....................................................................................................................................................... 8

4.1 Nominal heat output ...................................................................................................................................... 8

4.2 Load of fuel ........................................................................................................................................................ 8

4.2.1 Maximum load .................................................................................................................................................. 8

4.2.2 Minimum load .................................................................................................................................................. 9

4.3 Design of the essential dimensions .......................................................................................................... 9

4.3.1 Combustion chamber dimensions ............................................................................................................ 9

4.3.2 Calculated flue pipe length ....................................................................................................................... 10

4.3.3 Minimum flue pipe length ......................................................................................................................... 11

4.3.4 Gas groove profile ........................................................................................................................................ 12

4.4 Calculation of the burning rate ............................................................................................................... 13

4.5 Fixing of the air ratio .................................................................................................................................. 13

4.6 Combustion air flue gas .............................................................................................................................. 13

4.6.1 General ............................................................................................................................................................. 13

4.6.2 Combustion air flow rate ........................................................................................................................... 13

4.6.3 Flue gas flow rate ......................................................................................................................................... 14

4.6.4 Flue gas mass flow rate .............................................................................................................................. 15

4.7 Calculations of the density ........................................................................................................................ 15

4.7.1 Combustion air density .............................................................................................................................. 15

4.7.2 Flue gas density ............................................................................................................................................. 15

4.8 Calculation of the outside air temperature combustion air temperature and flue gas

temperature ................................................................................................................................................... 16

4.8.1 Mean outside air temperature and combustion air temperature .............................................. 16

4.8.2 Mean combustion chamber temperature ............................................................................................ 16

4.8.3 Flue gas temperature in the flue pipe ................................................................................................... 16

4.8.4 Flue gas temperature in the connecting pipe..................................................................................... 17

4.8.5 Flue gas temperature at chimney entrance mean flue gas temperature of the

chimney and temperature of the chimney wall at the top of the chimney .............................. 17

4.9 Calculation of flow mechanics ................................................................................................................. 17

4.9.1 General ............................................................................................................................................................. 17

4.9.2 Calculation of the standing pressure .................................................................................................... 17

4.9.3 Calculation of the flow velocity ............................................................................................................... 18

4.9.4 Calculation of the static friction .............................................................................................................. 18

4.9.5 Calculation of the resistance due to direction change .................................................................... 19

4.10 Operation control ......................................................................................................................................... 21

4.10.1 Pressure condition ...................................................................................................................................... 21

4.10.2 Dew point condition .................................................................................................................................... 21

4.10.3 Efficiency of the combustion η ................................................................................................................. 21

4.10.4 Flue gas triple of variates .......................................................................................................................... 22

Bibliography ................................................................................................................................................................. 23

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oSIST prEN 15544:2021
prEN 15544:2021 (E)
European foreword

This document (prEN 15544:2021) has been prepared by Technical Committee CEN/TC 295 “Residential

solid fuel burning appliances”, the secretariat of which is held by BSI.
This document is currently submitted to the CEN Enquiry.
This document will supersede EN 15544:2009.
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oSIST prEN 15544:2021
prEN 15544:2021 (E)
Introduction

This document specifies a calculation method for the dimensioning of Kachelgrundöfen/Putzgrundöfen

(tiled/mortared stoves).

The application of the calculations of this document enables a verification of the emission values carbon

monoxide, nitrogen dioxide, organically bound carbon as well as dust and the efficiency.

Complying with the calculations of this document results in emission values less or equal for carbon

3 3

monoxide 1 500 mg/m (1 000 mg/MJ), nitrogen dioxide 225 mg/m (150 mg/MJ), organically bound

n n
3 3

carbon 120 mg/m (80 mg/MJ) and dust 90 mg/m (60 mg/MJ). If the calculations of this document are

n n

used in combination with suitable combustion chambers that prove lower emission values in a type test,

these values are also considered to be complied with.

This calculation method for the dimensioning of Kachelgrundöfen/Putzgrundöfen (tiled/mortared

stoves) is based on appropriate literature as well as EN 13384-1, and where empirically determined

correlations are used in addition to physical and chemical formulas.

In case of a calculation method for different interior materials than fireclay the proof of the compliance

of the emission values and the efficiency should be delivered separately. Also, the empiric data of the

combustion chamber dimensions, the minimum flue pipe length, the burning rate as well as the

combustion chamber temperature and the decrease of the temperature along the flue pipe should also be

separately determined.
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oSIST prEN 15544:2021
prEN 15544:2021 (E)
1 Scope

This document specifies calculations for the dimensioning of Kachelgrundöfen/Putzgrundöfen

(tiled/mortared stoves) based upon the required nominal heat output of the stove as declared by the

producer. The Kachelgrundöfen/Putzgrundöfen (tiled/mortared stoves) are of individual one-off

construction design. The document can be used for log wood fired Kachelöfen (tiled stoves) that burn one

fuel load per storage period with a maximum load between 10 kg and 40 kg (log wood with water content

from 12 % to 20 %, thickness of 5 cm to 10 cm in diameter, length varies usually from 25 cm to 50 cm,

and is oriented toward the combustion chamber dimensions) and a storage period (nominal heating

time) between 8 h and 24 h.

This document is valid for Kachelgrundöfen/Putzgrundöfen (tiled/mortared stoves) equipped with

3 3

fireclay as interior material, with an apparent density between 1,750 kg/m and 2,300 kg/m , a degree

of porosity from 17 % up to 33 % by volume and a heat conductivity from 0,90 W/mK up to 1,30 W/mK

(temperature range 20 °C to 400 °C).

This document is valid for Kachelgrundöfen/Putzgrundöfen (tiled/mortared stoves) with combustion air

supply from the side via a heating door frame or the standing grate of the heating door into the

combustion chamber. The document is valid for an inflow speed of the combustion air between 2 m/s

and 4 m/s.

This document also applies to the combination with combustion chambers that are suitable for one-off

Kachelgrundöfen/Putzgrundöfen (tiled/mortared stoves) and for which compliance with the legally

required emission values has been verified as part of a type test by an accredited and/or notified body.

This document is applicable to combustion chambers:
• with an air-fuel ratio of between 1,95 and 3,95 according to the type test;
• with a maximum fuel less than 10 kg, but more than 5 kg;
• using other suitable materials as well as fireclay.

With regard to the type test, this document is applicable combustion chambers which are:

• from slow heat release appliances tested according to EN 15250 (or prEN 16510-2-5);

• inserts tested according to EN 13229 (or prEN 16510-2-2); or

• combustion chambers tested according to respective national standards (e.g. ÖNORM B 8303).

This document applies to type tested combustion chambers designed for batch fired pellet burning if

meeting the requirements according to this document (air-fuel ratio between 1.95 and 3,95, the load of

the pellets shall be burned in 78 ± 20 min).

This document is not valid for combinations with water heat exchangers for central heating or other heat

absorbing elements like open water tanks and glass plates greater than 1/5 of the combustion chamber

surface, etc. This document is not valid for mass-produced prefabricated stoves (slow heat release

appliances) or partly prefabricated stoves (slow heat release appliances) according to EN 15250.

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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 13384-1, Chimneys – Thermal and fluid dynamic calculation methods – Part 1: Chimneys serving one

heating combustion
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
air-fuel ratio

ratio between the amount of air supplied to the combustion and the theoretically required amount of air

3.2
calculated flue pipe length
length which is required to determine the flue gas temperatures in the flue pipe
3.3
construction with air gap
construction, with an air gap between the inner and the outer shell

Note 1 to entry: It is a construction with an air gap if the distance between the inner and outer shell is at least

2,5 cm and more than 50 % of the Kachelgrundofen/Putzgrundofen (tiled/mortared stove) is built in this way.3.4

3.4
construction without air gap
construction, with no air gap between the inner and the outer shell

Note 1 to entry: It is a construction with no air gap if the distance between the inner and outer shell is less than

2,5 cm and at least 50 % of the Kachelgrundofen/Putzgrundofen (tiled/mortared stove) is built in this way.

3.5
combustion chamber base

area of a horizontal cut through the combustion chamber at the height of the lower edge of the firebox

opening
3.6
combustion chamber height

mean vertical distance between the combustion chamber base and the combustion chamber ceiling

3.7
combustion chamber surface
sum of the inner surfaces of the combustion chamber
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oSIST prEN 15544:2021
prEN 15544:2021 (E)
3.8
mean combustion chamber temperature
value to calculate the thermal lift in the combustion chamber
3.9
burning rate
mean fuel load divided by burning time
3.10
combustion chamber admeasurement
admeasurement of the combustion chamber base
3.11
gas groove
additional opening for the conduction of the flue gas
3.12
flue pipe length

length of the connecting line of all geometric centres of the flue pipe profiles from the combustion

chamber exit to the connecting pipe entrance
3.13
Kachelgrundofen
tiled stove
Kachelofen

one off slow heat release appliance, which is adapted individually to local conditions and whose visible

surface is predominantly made of tiles
3.14
short flue pipe section

section of the flue pipe, where the length of the section is shorter than the hydraulic diameter

3.15
minimum flue pipe length
Zmin
minimal acceptable length of the flue pipe
3.16
maximum load
load of the fuel at nominal heat output
3.17
minimum load
Bmin
load of the fuel at the lowest reduced heat output
3.18
nominal heat output
mean useable heat output of the heating appliance
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oSIST prEN 15544:2021
prEN 15544:2021 (E)
3.19
Putzgrundofen
mortared stove
Putzofen

one off slow heat release appliance, which is adapted individually to local conditions and whose visible

surface is predominantly plastered
3.20
storage period
nominal heating time

period of time specified by the producer where the nominal heat output is set free

3.21
efficiency

proportion (in percent) of the nominal heat output multiplied with the storage period to the total heat

input
4 Calculations
4.1 Nominal heat output

The nominal heat output (P of the stove shall be specified by the manufacturer so that the values of the

stove can be calculated according to 4.2 to 4.10. When specified to heat a full house or building unit, the

nominal heat output (Pn) shall correspond to the design heating load of the room or rooms to be heated.

In the case of partial heating, in which only part of the design heating load of the installation room is

covered, the nominal heat output (Pn) can be selected lower.
4.2 Load of fuel
4.2.1 Maximum load

The maximum load shall be at least 5 kg of fuel and shall be calculated as follows:

P⋅t
n n
m = (1)
min
⋅4.16
100
NOTE 1 To calculate, a net calorific value of wood of 4,16 kWh*kg is presumed.
where
m is the maximum load (kg);
P is the specified nominal heat output (kW);
t is the specified storage period (h);
η required minimum efficiency in %.
min
NOTE 2 The storage period can vary between 8 h and 24 h.

If tested combustion chambers are used, the maximum load at nominal heat output shall be the maximum

fuel mass according to the type test.
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4.2.2 Minimum load

The definition and calculation of the minimum load is only necessary if a reduced heat output is declared

by the manufacturer. The minimum load shall be calculated as 50 % of the maximum load as follows:

mm0.5⋅ (2)
Bmin B
where
m is the maximum load (kg);
m is the minimum load (kg).
Bmin

If tested combustion chambers are used, the minimum load at reduced heat output shall be the minimum

fuel mass according to the type test. The share can deviate from the 50 % according to Formula (2).

4.3 Design of the essential dimensions
4.3.1 Combustion chamber dimensions
4.3.1.1 General

The height of the lowest opening shall be at least 5 cm above the floor of the combustion chamber.

NOTE Designing the dimensions of the combustion chamber serves two main purposes: firstly to ensure that

sufficient room is available to contain the fuel needed to be charged and secondly that the requirements for clean

combustion are met. Clause 4.3.1 does not apply to tested combustion chambers.
4.3.1.2 Combustion chamber surface
The dimension of the combustion chamber surface shall be calculated as follows:
O 900×m (3)
BR B
where
m is the maximum load (in kg);
O is the combustion chamber surface (in cm ).

For the calculation of the combustion chamber surface all its walls, the ceiling and the base including the

area of the combustion chamber opening and the combustion chamber exit for the flue gas shall be

regarded equally i.e. calculated as if there were no combustion openings or exits.

4.3.1.3 Combustion chamber base
The combustion chamber base can be varied between a minimum and a maximum value.
The minimum value results from the requirement that at maxi
...