Metallic ventilation cap for biomass wood pellet stores. This cap is used to prevent the build up of Carbon Monoxide in unvented pellet stores. All wood pellet stores should have at least one ventilation cap if the store has no other method of ventilation. Manufactured with an aluminium Storz coupling, a stainless mesh and cowl, this cap provides much more ventilation for your store than our plastic vented cap. This is particularly important when there is no other way to release the carbon monoxide build up. This cap is also more suitable for locating in full sun, where they will give a better service life.