Your dehumidifier can acquire a musty smell from the ambient air, dust and pet dander. It can also smell if it has not been in use for a while and there has been a lack of maintenance.
Our ambient air contains a multitude of different types of odour from our day to day activities, such as cooking, clothing, healthcare products (e.g. hairspray, deodorant, perfumes), dirt and dust. These odours are then absorbed by the dehumidifier and become concentrated in the appliance, leading to a musty smell.
Over time, excessive dust build-up on the filters can seep into the internal parts of the dehumidifier and aggravate the odour further. If left for longer periods, it can even cause overheating and failure.
To prevent this smell, it is important to have routine maintenance and an annual service will help to keep your dehumidifier hygienic. Check the links below for a couple tips on how to maintain your dehumidifier.