Despite efforts to accelerate building renovations across Europe, the current renovation rate remains low. At the same time, many fossil fuel-based gas boilers will need replacement in the near future. Heat pumps present an attractive alternative as they offer a high efficiency and electricity is increasingly being produced from renewable sources. However, it is commonly recommended to perform advanced energetic renovations before installing heat pumps, as their efficiency and ability to deliver thermal comfort in partially renovated buildings is frequently questioned. Therefore, this study investigates and compares the energetic performance and reached thermal comfort of air-source heat pumps with a gas condensing boiler in a terraced house after intermediate and advanced renovation. Results show that both air-to-water and air-to-air heat pumps can achieve the desired thermal comfort when the appropriate temperature set points are implemented and that its installation reduces primary energy use compared to gas boilers in both renovation scenarios. Air-to-air heat pumps use 27.7 to 44.3% less electricity compared to air-to-water heat pumps after advanced and intermediate renovation respectively. These findings suggest that air-source heat pumps are a viable solution for partially renovated buildings and can be implemented immediately.