🔥 Testing of solid-fuel boilers with an output up to 500 kW — safety, efficiency and emissions — PN-EN 303-5

Construction PN-EN 303-5

Overview

SCOPE FROM THE PKN CATALOGUE CARD, QUOTED VERBATIM (clause 1.1 "General") (our translation): "This document applies to heating boilers, including safety devices, with a nominal heat output of up to 500 kW, which are designed exclusively for burning solid fuels, operated in accordance with the accompanying instructions and protected by the manufacturer against improper use. This document also applies to solid-fuel heating boilers that take combustion air from outside the building and to appliances with a sealed combustion chamber. […] Heating boilers may operate with natural or forced draught. Fuel may be charged manually or automatically. Heating boilers may operate in non-condensing or condensing mode."

THE STANDARD ALSO COVERS ACCESSORIES, NOT ONLY THE BOILER ITSELF. The card says this explicitly: "This document contains requirements and test methods concerning the safety, combustion performance, operating characteristics, marking and maintenance of heating boilers. It also covers all external equipment that has an influence on the safety systems (e.g. a device to prevent burn-back, an integrated fuel hopper)." (our translation). This settles the dispute about the scope of an order: testing a boiler with an automatic feeder also covers the protection against burn-back into the hopper, because it belongs to the safety system. This is independently confirmed by the certification body OBAC, describing the tests carried out within the certification of boilers.

LIMITS OF THE WATER SYSTEM — TWO NUMBERS THAT MUST BE CHECKED BEFORE ACCEPTING THE ORDER. The scope gives them together with the condition to which they refer: boilers according to this document are intended for central heating installations in which the heat carrier is water with a maximum allowable temperature of up to 110 °C, and which will be operated at a maximum allowable operating pressure of up to 6 bar. A boiler with higher allowable parameters falls outside the scope of this standard.

THE BURNER MUST BE INTEGRATED WITH THE BOILER — WITH ONE EXCEPTION. Scope (our translation): "This document applies only to heating boilers with a burner forming a unit integrated with the heating boiler. This document applies to units consisting of a boiler body and a burner conforming to EN 15270:2007 only when this unit is tested according to this document." In other words: a set of "third-party body + third-party pellet burner" may be tested according to 303-5, but as a whole, and not by adding up two separate tests.

FIVE EXCLUSIONS LISTED IN THE SCOPE. The standard does not apply to: (1) heating boilers and other heating appliances designed to also heat directly the room in which they are installed — also in accordance with Regulation 2015/1185/EU; (2) cooking appliances; (3) the design and construction of external fuel stores and automatic fuel feeders located BEFORE the safety devices of the boiler; (4) manually charged straw-fired heating boilers; (5) combined heat and power (CHP) appliances. The first exclusion is the boundary with the PN-EN 16510 series: an appliance that gives off heat directly to the room is a local space heater, not a boiler.

A SENTENCE ABOUT THE DATE THAT IS EASY TO OVERLOOK. The card ends the scope with a reservation (our translation): "This document does not apply to heating boilers that were tested before the date of its publication as an EN (European Standard)." A test carried out under an earlier edition does not therefore automatically become a test according to the new edition — and conversely, the new edition is not applied retroactively to products already tested.

TWO DATES WITH ONE DESIGNATION. The document bears the designation PN-EN 303-5+A1:2023-05, and its POLISH VERSION appeared on 20-02-2026. The designation of the standard and the date on which the translation was made available are two different things — in the accreditation scope and in the report the designation is cited, never the date of publication of a language version.

A NOTE ON A SOURCE DESCRIBING AN OLDER EDITION. The material of the certification body OBAC quoted below refers to the PN-EN 303-5:2012 edition and quotes its scope. The content of that scope coincides with the current edition as regards the subject of the test (safety, combustion quality, operating characteristics, marking, maintenance, accessories affecting safety), but it is a different edition and must be treated as such — as confirmation of the subject of the standard, not as a source of its current requirements.

REFERENCE CONDITIONS AND LIMIT VALUES — NOT FROM THE STANDARD, BUT FROM THE REGULATION. A basis separate from the standard is Commission Regulation (EU) 2015/1189 (ecodesign for solid fuel boilers), which applies to boilers with a rated heat output of 500 kW or less — that is, to the same output range as PN-EN 303-5. Its Annex III "Measurements and calculations" gives the reference conditions verbatim (our translation of the Polish text): "Emissions of particulate matter, organic gaseous compounds, carbon monoxide and nitrogen oxides shall be expressed in standardised terms as dry flue gas at an oxygen content of 10 % and in standard conditions — at a temperature of 0 °C and at a pressure of 1 013 millibars." Annex II "Ecodesign requirements" gives the values applicable from 1 January 2020: seasonal space heating energy efficiency not less than 75 % for boilers with a rated heat output of 20 kW or less and not less than 77 % for boilers with an output above 20 kW; emissions of particulate matter not higher than 40 mg/m³ with automatic fuel feeding and 60 mg/m³ with manual feeding; of organic gaseous compounds — 20 mg/m³ with automatic and 30 mg/m³ with manual; of carbon monoxide — 500 mg/m³ with automatic and 700 mg/m³ with manual; of nitrogen oxides expressed as nitrogen dioxide equivalent — 200 mg/m³ for biomass boilers and 350 mg/m³ for fossil fuel boilers. All these values refer to the conditions quoted above: dry flue gas, 10 % oxygen, 0 °C, 1 013 mbar.

THE FOUR EXCLUSIONS OF THE REGULATION ARE NOT THE SAME AS THE EXCLUSIONS IN THE STANDARD. The regulation does not apply to: boilers generating heat only for the purpose of providing hot drinking or sanitary water; boilers for heating and distributing gaseous heat transfer media (steam, air); cogeneration boilers with a maximum electrical capacity of 50 kW or more; non-woody biomass boilers. The standard has its own five exclusions, listed above, and both lists must be checked separately — a boiler may be outside the scope of one and within the scope of the other.

THE BOUNDARY WITH LOCAL SPACE HEATERS. The values and reference conditions given above concern BOILERS. For solid fuel local space heaters — that is, for the appliances covered by the PN-EN 16510 series — a separate Commission Regulation (EU) 2015/1185 applies, whose text we did not have. The 10 % oxygen content and the limit values from the regulation on boilers MUST NOT be transferred to space heaters.

WHAT WE DO NOT GIVE. We did not have the text of the standard — PKN sells it. That is why WE DO NOT GIVE FROM THE TEXT OF THE STANDARD: the emission and efficiency limit values for the individual boiler classes (the ecodesign thresholds, given in the list of parameters above, come from Regulation (EU) 2015/1189 and are something other than the classes of the standard), the conditions for carrying out the test (test fuel, loads, durations), the method of referring concentrations to the oxygen content of the flue gas, the requirements for instruments or the rules for calculating the results. All this is the content of the standard and must be taken from its text.

Method principle

The boiler is installed on a test rig with a water system and a flue, and then tests are carried out at nominal and partial load, burning the test fuel specified in the standard. Thermal quantities (output, temperatures, flows, fuel mass) and the composition of the flue gas are measured simultaneously, determining the thermal efficiency and the concentrations of pollutants referred to the oxygen content in the flue gas adopted in the standard. A separate group are the safety tests — of the operation of the safety devices, including the protection against burn-back into the fuel hopper. The conditions, limits and method of calculation are given by the standard itself, whose text we do not have.

Applications

• Type testing of solid-fuel boilers before placing on the market
• Certification of boilers by a product certification body
• Assignment of a boiler to the class to which anti-smog resolutions and subsidy programmes refer
• Control tests within factory production control at the boiler manufacturer
• Assessment of the safety devices of a boiler with an automatic feeder, including the protection against burn-back

Key parameters

Standard

Standard number

PN-EN 303-5+A1:2023-05 (wersja polska; wprowadza EN 303-5:2021+A1:2022 [IDT])

Title (PL)

Kotły grzewcze — Część 5: Kotły grzewcze na paliwa stałe z ręcznym i automatycznym zasypem paliwa o nominalnej mocy cieplnej do 500 kW — Terminologia, wymagania, badania i oznakowanie

Title (EN)

Heating boilers — Part 5: Heating boilers for solid fuels, manually and automatically fired, nominal heat output of up to 500 kW — Terminology, requirements, testing and marking

Step-by-step procedure

1. Checking whether the boiler falls within the scope of the standard

   Establish the nominal heat output (up to 500 kW) and the maximum allowable water temperature (up to 110 °C) and the maximum allowable operating pressure (up to 6 bar). Check the five exclusions from the scope, in particular whether the appliance does not also heat directly the room in which it stands — such an appliance belongs to the PN-EN 16510 series, not to 303-5.

2. Establishing the boundaries of the test object

   Include in the test also the external equipment affecting the safety systems: the protection against burn-back and the integrated fuel hopper. An external fuel store and a feeder located before the safety devices of the boiler are excluded.

3. Checking the body–burner unit

   If the burner is not integrated, establish whether the unit is tested as a whole according to this standard — only then does the document apply to a set with a burner conforming to EN 15270:2007.

4. Installation of the boiler on the rig

   Connection to the water system and the flue, setting of the draught. WE DO NOT GIVE THE DETAILS OF THE INSTALLATION AND THE DRAUGHT VALUES — they are in the text of the standard.

5. Tests at nominal and partial load

   Burning of the test fuel with simultaneous measurement of thermal quantities and of the composition of the flue gas. WE DO NOT GIVE THE CONDITIONS, DURATIONS AND THE METHOD OF FIRING.

6. Safety tests

   Checking the operation of the control and safety devices, including the protection against burn-back into the hopper. The scope and criteria are given by the standard.

7. Compilation of results and marking

   Efficiency and emissions are compiled in the report together with the reference conditions; on this basis the requirements for the marking of the boiler are fulfilled. WE DO NOT GIVE THE METHOD OF CALCULATION AND THE LIMIT VALUES FROM THE STANDARD.

8. Referring the result to the ecodesign requirements

   If the test serves to demonstrate conformity with Regulation (EU) 2015/1189, emissions are expressed for dry flue gas at an oxygen content of 10 % and at a temperature of 0 °C and a pressure of 1 013 mbar, and the results are compared with the values from Annex II. Check at the same time the four exclusions of the regulation — they are different from the five exclusions of the standard.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The test is carried out on an operating boiler — hot surfaces and hot water under pressure; protective clothing and gloves are mandatory
• Carbon monoxide is odourless and deadly toxic — the rig requires a CO detector and effective ventilation
• The protection against burn-back is tested deliberately under conditions of a risk of ignition of the fuel in the feeder — the procedure requires a separate risk assessment
• Water system at an operating pressure of up to 6 bar — before the test check the tightness and the safety valves of the rig
• Ash and unburnt fuel are removed after cooling down, into non-combustible containers

Frequently asked questions