Last updated: 1 May 2026
A wood-burning insert is a closed combustion appliance designed to fit into an existing open fireplace opening or a purpose-built masonry recess. Unlike a freestanding stove, an insert uses the surrounding masonry as part of its housing, which changes how heat is distributed and how the flue connection must be configured.
In Poland, insert installations are subject to EN 13240 (for room heaters burning solid fuel) and PN-B-02871 (positioning of fixed solid-fuel appliances). Before specifying an insert, the existing chimney must be assessed for flue cross-section, height, and condition — since most older Polish masonry chimneys were built for open fires and may need relining for use with a closed appliance.
Insert Types by Combustion System
Convection Inserts
Convection inserts draw room air through channels around the firebox and return it to the room as heated air. They respond quickly to fire and distribute warmth across a larger area than radiant models. Output ranges from 5 kW to 14 kW for residential models. Convection inserts are well suited to open-plan layouts where air movement can carry heat into adjacent rooms.
Accumulating Inserts
Accumulating inserts use soapstone, ceramic, or chamotte (fireclay) cladding panels that absorb heat during combustion and release it gradually over 8–12 hours. During burning, surface temperatures may exceed 100°C; after the fire dies down, the cladding continues to emit radiant heat at 60–80°C. These inserts are suited to well-insulated rooms where steady background heat is preferred over immediate high output.
Inserts with Water Jacket
Water-jacket inserts (wkłady z płaszczem wodnym) connect to a central heating circuit. A proportion of the combustion output — typically 60–70% — is transferred to the water loop, with the remainder contributing to room heating. EN 13229 applies to these appliances. They require a buffer tank (zbiornik buforowy) of at least 30 litres per kW of water-side output to prevent overheating if the pump fails.
Firebox Dimensions and Opening Compatibility
Insert width is measured at the widest point of the outer frame (rama). The firebox opening in the masonry must be equal to or larger than the insert body — typically with 10–20 mm clearance on each side for thermal expansion. The following table shows typical insert body dimensions for common output ratings:
| Output (kW) | Body width (mm) | Body height (mm) | Body depth (mm) | Flue outlet (mm) |
|---|---|---|---|---|
| 5–7 | 560–640 | 420–480 | 340–380 | 150 |
| 8–10 | 640–720 | 480–540 | 360–420 | 150–180 |
| 11–14 | 720–840 | 520–600 | 400–460 | 180–200 |
| 15–25 | 840–1000 | 580–680 | 440–520 | 200–250 |
These ranges are representative across European manufacturers. Exact dimensions must be taken from the manufacturer's installation manual for the specific model.
Efficiency Ratings Under EN 13240
EN 13240 specifies the test method for room heaters burning solid fuel. The standard defines two test conditions: nominal heat output and reduced heat output (approximately 50% of nominal). Efficiency is measured as net calorific efficiency — the ratio of useful heat output to energy content of the fuel consumed.
Under the EU Ecodesign Regulation (EU) 2015/1185, wood-burning room heaters placed on the EU market from 2022 onwards must achieve a seasonal space heating energy efficiency (ηs) of at least 65% for batch-fed appliances. In practice, most current-generation inserts achieve 75–82% efficiency at nominal output.
The efficiency figure on a product datasheet is measured at test conditions (typically 12–13% moisture content beech logs). Real-world efficiency depends on fuel quality, log moisture, firing technique, and whether the appliance is operated near its nominal output range.
Clearance Distances and Safety Requirements
PN-B-02871 defines minimum clearance distances from combustible construction materials to the surfaces of solid-fuel appliances. For an insert embedded in a masonry surround, the critical distances are:
- From the front glass panel to combustible furniture: minimum 1000 mm in the ash-fall zone, 500 mm laterally
- From the flue connection to combustible ceiling material: minimum 500 mm unless the ceiling is fully non-combustible
- From the outer insert frame to timber lintel above the opening: minimum 150 mm, or as specified by the manufacturer (whichever is greater)
The insert must rest on a non-combustible hearth pad extending at least 300 mm in front of the door and 150 mm on each side. In practice, most Polish building inspectors (during odbiór kominiarski) require the hearth to be flush with the surrounding floor and to be of ceramic tile, natural stone, or concrete construction.
Combustion Air Supply
Closed-combustion inserts require a dedicated air supply when the building has mechanical extract ventilation (e.g. bathroom fans, kitchen hoods) or when the room has been insulated to a level where natural infiltration is insufficient. EN 15287-1 provides guidance on combustion air supply calculations. A standard single-family insert of 8 kW nominal output requires approximately 10–12 m³/h of combustion air.
For installations in newer Polish buildings meeting WT 2021 thermal envelope standards, a dedicated external air supply duct (kanał powietrza zewnętrznego) connected directly to the insert air inlet is typically required. Some insert manufacturers supply kits with 80–100 mm flexible duct and a floor or wall terminal.
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External references: PKN (Polish Committee for Standardization) — EU Ecodesign Regulation 2015/1185