Wood-fuelled Stoves – Selection Criteria

What is a wood-fuelled stove?

Wood-fuelled (biomass) stoves burn wood pellets, chips or logs to provide warmth in a single room. Usually, the stove isn’t connected to your radiators, but it may produce hot water using a back boiler. Therefore, a wood-fuelled stove is typically installed in addition to another form of heating.

For more details and a general overview of what these products are, please see our Product Guide. For biomass boilers that provide distributed central heating using wood pellets or logs please see our pages for biomass boilers.

Introduction

This page details the selection criteria applied to wood-fuelled stoves on toptenuk.org. Only products that reach the minimum criteria specified below are displayed on the website. This guide only covers wood-fuelled stoves designed to provide heating for a single room. For more details and a general overview of what these products are, please see our Product Guide. For biomass boilers that provide distributed central heating using wood pellets or logs please see our pages for biomass boilers.

Selection Criteria

The minimum criteria to be shown on toptenuk.org is shown in Table 1 which covers both the energy efficiency of the system as well as air quality factors, a key consideration when burning wood.

Table 1: Current selection criteria for local space heaters. This covers both energy efficiency and air quality factors.

Criteria	Pellets (automatic)	Logwood (manual)
Energy label	A+ or higher	A+ or higher
Particulate Matter [mg/m3]	<20	<40
CO nominal load [mg/m3]	<300	<1500
Organic Gaseous Compounds nominal load [mg/m3]	<60	<120
NOx [mg/m3]	<200	<200

Relevant Regulations

The following regulations were the basis for the above selection criteria for wood-fuelled stoves. For consistency with the rest of this document, we use the term wood-fuelled stoves, however, the term used in the regulations is local space heaters.

Energy Labelling (EU 2015/1186)

Since January 1^st 2018, wood-fuelled stoves should come with an energy efficiency label, to provide information on the brand, the model, the energy efficient class, the direct and, if applicable, the indirect rated heat output. This labelling is compulsory for appliances with rated output up to 50 kW. Table 2 shows the details of the information contained in an energy label

Table 2: Energy Labelling

The Energy Efficiency Index (EEI) is defined using :

EEI = (η_S,on x BLF) - 10% - F(2) + F(3) - F(4) - F(5)

Where,

ΗS,on	is the seasonal space heating energy efficiency in active mode (%)
BLF	is the biomass label factor (1.45 for biomass, 1 for fossil fuel)
F(2), F(3)	account for changes to the EEI due to heating controls
F(4)	account for changes to the EEI due to auxiliary electricity consumption
F(5)	account for changes to the EEI due to a permanent pilot flame

For more details on how these values are calculated, please refer to the regulation document: EU 2015/1186. Once calculated, individual products are categorised into energy efficiency classes using Table 3.

Table 3: Definition of the Energy Efficiency Class of wood-fuelled stoves

Energy efficiency class	Energy efficiency index (EEI)
A++	EEI ≥ 130
A+	107 ≤ EEI < 130
A	88 ≤ EEI < 107
B	82 ≤ EEI < 88
C	77 ≤ EEI < 82
D	72 ≤ EEI < 77
E	62 ≤ EEI < 72
F	42 ≤ EEI < 62
G	EEI < 42

Ecodesign (EU 2015/1185)

This regulation applies to appliances up to 50 kW and covers both efficiency and air quality measures. The requirements will become legally binding by January 1^st 2022. The criteria for the various types are given in Table 4.

Table 4: Ecodesign criteria for local space heaters less than 50 kW

Criteria	Pellets (closed)	Logwood (closed)	Logwood (open)
Efficiency at rated load (%)	≥79	≥65	≥30
Particulate Matter [mg/m3]	≤20	≤40	≤50
CO nominal load [mg/m3]	≤300	≤1500	≤2000
Organic Gaseous Compounds nominal load [mg/m3]	≤60	≤120	≤120
NOx [mg/m3]	≤200	≤200	≤200

Future Changes

With the Ecodesign requirements from EU 2015/1185 coming into action in 2022, criteria on air quality will become stricter. A preliminary estimate of how this will effect the selection criteria requirements is included in Table 5.

Table 5: Expected Top Ten selection criteria for local space heaters in 2022

Criteria	Pellet stoves	Logwood stoves
Energy label	A++	A++
Particulate Matter [mg/m3]	<15	<35
CO nominal load [mg/m3]	<250	<1000
Organic Gaseous Compounds nominal load [mg/m3]	<20	<65
NOx [mg/m3]	<180	<180

Glossary

• Particulate matter nominal load (mg/Nm³): specifies the particulate matter in the exhaust air at nominal load of the stove. Particulate matter is the microscopic particles of solid or liquid matter suspended in the air, and high levels of particulate matter can be hazardous to our health.
• CO nominal load (mg/Nm³): specifies carbon monoxide in the exhaust air at nominal load of the stove.
• Organic gaseous compounds nominal load (mg/Nm³) : specifies the organic carbon in the exhaust air at nominal load of the stove.
• NOx (mg/Nm³): specifies nitrogen dioxide in the exhaust air at nominal load of the stove.
• EU Regulation for energy labelling of local space heaters; https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A32015R1186

Links

EU regulation for ecodesign requirements for solid fuel local space heaters; https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A32015R1185&qid=1603278122877