How to store wood pellets to avoid carbon monoxide risk at French home

Wood pellets, commonly used in stoves and boilers in homes across France, can release carbon monoxide (CO) during storage even without being burned, reports the French Agency for Food, Environmental and Occupational Health & Safety (ANSES).

Natural chemical reactions inside the pellets, particularly the oxidation of fatty acids in the wood, can cause them to heat up slightly and release gases without any combustion.

In addition to carbon monoxide, stored pellets can emit other gases such as carbon dioxide (CO₂), methane (CH₄), and volatile organic compounds (VOCs). These processes can also reduce the amount of oxygen in the surrounding air.

ANSES says these emissions are usually low and gradual - but tend to increase at higher temperatures. They decrease over time. The type of wood is a factor with, for example, pine pellets likely to emit more gases than spruce.

Although the overall risk is limited, the agency confirms that cases of carbon monoxide poisoning linked to pellet storage have been reported, particularly in workplaces or experimental conditions. 

The main danger arises in confined or poorly ventilated spaces, where gases can build up.

In practice, wood pellet stoves are widely used in France, although readers have reported concerns about installation, maintenance costs and after-sales support.

While incidents remain rare, carbon monoxide is highly toxic. At high concentrations, it can cause serious poisoning, leading to symptoms such as respiratory distress, convulsions, coma, and in extreme cases, death. 

The tricky part is that it can not be smelt, seen or tasted making the risk hard to identify. This was the case for an 87-year-old man in Haut-Rhin in 2025. The man stored several tonnes of wood pellets in his basement, which was not properly ventilated or isolated from the rest of the house. Carbon monoxide built up from the pellets and gradually spread into the living areas without being detected. The man was later found conscious but intoxicated and taken to hospital for treatment by emergency services. 

How to properly store wood pellets 

ANSES recommends storing pellets in well-ventilated areas and avoiding enclosed spaces.

Pellets should be kept in cool and dry locations, away from humid environments. If stored indoors, once opened, they should be placed in airtight containers and kept on a pallet covered with cardboard. If stored outdoors, they should be placed on elevated ground, protected from wind and rain, and covered with a tarp.

One tip when stacking pellet bags is to alternate the direction of each row to help prevent moisture from entering. Additionally, pellets should be kept away from heat sources such as direct sunlight, grills, fireplaces, water heaters, or any other appliance that radiates heat.

During summer, any leftover pellets should be stored away from water sources, such as pools and sprinklers, as well as heat sources, as they can self-heat and ignite, especially when they have high moisture concentrations, at temperatures often below 100C.