In order to solve the problem of low relative humidity in buildings and dispersion of existing heating and humidification equipment during the heating season in severe cold regions, a fan coil unit prototype with a humidification module was developed, and the heat is provided by an air source heat pump. The humidification module was made of parallel porous plates, which were infiltrated by the water using principle of capillary siphon. To explore the performance of the unit, an experimental bench was established in Harbin, China. The results show that the developed prototype can provide above 40 % RH while maintaining the room temperature. The heat absorbed by the water evaporation of the rated humidification capacity only accounts for 3.6 % of the nominal heating capacity of the fan coil unit. When unorganized fresh air infiltrated into the building, compared with the case of no humidification, the humidification reduced the temperature only 0.3 °C, the average relative humidity was increased by 33.8 %, the average humidity ratio was increased by 5.7 g/kg in the indoor stable phase, and the predicted percent dissatisfied in the standing occupant decreases to 9.55. Even if 30 m³/h of fresh air with low temperature and humidity was introduced into the building, the unit can ensure that the indoor temperature was above 20 °C and the relative humidity can be maintained at 30 %. In addition, in the rising stage of temperature and humidity, the humidification capacity of the unit is above 200 g/h.