The pursuit of reducing energy consumption and enhancing thermal efficiency across various sectors to foster sustainable practices has gained significant prominence in recent years, driven by the global environmental crisis. Sweco consultancy has undertaken a study focusing on underfloor heating systems for bathrooms in low-energy buildings located in Sweden. The objective is to analyse the energy usage and thermal loss to the ground based on the thickness of insulation employed. Literature findings indicate that the thermal loss to the ground should comprise approximately 15 % of the total energy, and there exists a logarithmic relationship between the thermal conductivity and density of the insulation material. In the present study, multiple simulation models were developed using IDA-ICE to assess the supplied energy and the percentage of heating loss through the ground for two typical bathrooms situated on adjacent floors of a residential building in Stockholm. The analysis encompasses scenarios where the construction is directly built on the soil or on a concrete slab, as well as the potential thermal loss from the upper level bathroom to the lower level. The results demonstrate that without an insulation layer the heating loss through the ground is remarkably high, approximately 60 %. When employing an insulation thickness of 200 mm or greater, the distinction between constructing on a concrete slab or on the soil becomes negligible. Furthermore, with a 300 mm insulation thickness, the heating loss percentage decreases to over 15 %. The simulations also reveal that the lower level bathroom can benefit from the energy loss occurring in the upper level bathroom. In instances where there is no insulation, the upper level experiences a 56 % energy loss, resulting in energy savings of over 70 % for the lower level bathroom. By incorporating a 45 mm insulation thickness on the upper level floor, this percentage is reduced to 13 %, leading to energy savings of over 25 % for the lower level bathroom.