The planned energy retrofitting of a residential building in Bologna, North-Center Italy is presented. The building is a detached house with an unheated basement, three floors with 2 apartments each, and an unheated attic. The total heated floor area is 281.9 m². The external wall is made of solid bricks and most windows are single glazed; no thermal insulation is present. Space heating is supplied by means of a gas boiler and radiators in the rooms. DHW is supplied by single-apartment electric boilers in 5 apartments and by a gas boiler in one apartment. Lighting is obtained by incandescent lamps. The proposed retrofitting includes: external thermal insulation of the vertical walls by calcium silicate hydrates and loft insulation by mineral wool; replacement of windows; installation of a multifunction air-to-water heat pump for heating, cooling and DHW; replacement of the radiators by new heat exchangers; LED lighting; installation of PV panels. The building has been simulated by TRNSYS 17, and the heat pump has been simulated by a own MATLAB code. The retrofitting will reduce the total annual use of primary energy (excluding appliances) from 377.9 to 44.8 kWh/m², and will provide also summer cooling and dehumidifying, now not available.