Many New Zealand residential homes suffer from poor indoor environmental quality (IEQ). Cold, damp, and mould-ridden homes can cause serious respiratory health problems. Poor IEQ can arise due to poor insulation and ventilation, and is compounded when residents cannot afford heating. Features of the residential building code mean many New Zealand houses built under old standards lack wall insulation, have single glazing on windows and are poorly ventilated. A major indicator of poor IEQ is mould growth, which can cause, or exacerbate, respiratory illness. This project assesses the results of modifying an existing dehumidifier to include ultraviolet germicidal (UVGI) lights and two different types of filters (CityPleat and 30/30). The original device altered IEQ by removing moisture. The modified device was designed to further improve IEQ by performing filtration and purification of the air, with the addition of the CityPleat, 30/30 filters with the UVGI lights. This project investigates the impact on various IEQ elements, such as room temperature, particulate matters (PM2.5), and relative humidity using an air imaging sensor (compatible with current WHO guidelines), with a focus on mould growth. We found the different filtration scenarios presented reduced the relative humidity effectively in the room compared to the baseline dehumidifier action only. The results show that adding the 30/30 filter with the UVGI lights increased the room temperature by 2.2oC, reduced the relative humidity by 10%, and reduced the PM2.5 values from 2.5 µg/m³ to 0.4 µg/m³ in the room after three hours of operation. Mould growth, as measured in agar plate coverage, was also reduced by the addition of the filtration and UVGI lights.