This study investigates the accuracy of EN ISO 13370 simplified method to consider the impact of floor edge insulation on ground-coupled heat loss, in comparison to both steady-state (software Therm) and dynamic (software Delphin and Voltra) simulation models. A comprehensive analysis was conducted on 78 distinct combinations of floor insulation thickness and additional vertical/horizontal edge insulation. The findings reveal that the standard procedure tends to overestimate heat loss for uninsulated or minimally insulated floors, as indicated by both steady-state and dynamic simulations. The simulations also show a decline in accuracy for insulation thicknesses between 100–400 mm when compared to dynamic models. This decline in accuracy is attributed to the EN ISO standard not accounting for floor/wall thermal bridge heat loss, rather than being a result of the standard not being developed for well-insulated floors. This assessment of ground-coupled heat loss compares steady-state and dynamic simulations to the current EN ISO 13370 procedure on various combinations of entire floor and edge insulation thickness in a seasonal frost region. The results imply that with increasing insulation thickness, the relative error of standard procedure increases. Further research on various floor geometries and climates can give input for refining current standard procedures to enhance accuracy.