## 5 Conclusions
When wood conductivity was highest (0.20 W/(m\(\cdot\)K) to 0.26 W/(m\(\cdot\)K)), comfort was maximised in a greater percentage of cases than when it was lowest, although in this case, the highest comfort levels were found in 14% of cases with conductivities under 0.10 W/(m\(\cdot\)K) and 16% of cases with values of 0.10 to 0.12 W/(m\(\cdot\)K). Conductivities of 0.18 W/(m\(\cdot\)K) often increased the start-up lag time by only 15 min in well-insulated, low-energy-demand dwellings and in nearly all such dwellings, the conductivity value increases it by 30 min. On these grounds, wood with high thermal conductivity cannot be said to always be necessary for the design of radiant floors. * One of the conclusions of this study that may be of most immediate interest is that the lowest thermal conductivity and thickest floor covering, i.e., wood flooring with the highest thermal resistance (even more of 0.15 m\({}^{2}\)K/W value) does not significantly affect the energy demand or thermal comfort. On average, wood flooring lowered energy demand by 6.4% and daily hours of thermal comfort by a mere 1.6% relative to granite coverings. * The findings on the thermal resistance of wood coverings provided no justification for establishing an upper limit that must not be exceeded in the selection of woods for radiant floors. Although European standard EN 1264-2 [85] makes no provision for coverings with thermal resistance values of over 0.15 m\({}^{2}\)K/W, they are not explicitly prohibited. In fact, thermal resistance values higher than 0.15 m\({}^{2}\)K/W did not raise energy demand significantly, nor did they lower the number of comfort hours in the vast majority of the conditions simulated. This study consequently suggests that the standard should be revised and the reference to that value deleted, since manufacturers have misconstrued it to be a limit not to be exceeded in the design of wood-covered radiant flooring. * It was shown that the thermal behavior of radiant floor heating systems is closely linked to building conditions and, therefore, it is necessary to carry out a technical study for each particular case. Our approach is based on the following three variables: (1) energy demand, (2) thermal comfort, and (3) start-up lag period. From our point of view, with these three variables, the overall performance of radiant floor heating can be clearly evaluated when its behaviour in transient mode coupled to the building needs to be assessed. The objective, as with any heating system, is to achieve thermal comfort for as long as possible with the lowest energy consumption. This can be analysed by using these two variables: the time in which comfort conditions are achieved and the energy demand of the radiant floor. On the other hand, the time required to achieve thermal comfort from an initial condition that is far from comfortable can be relevant for certain applications. Other approaches, such as the analysis of the power of the systems, or the surface temperature distribution of the floor (for hot and cold spots) may be of interest for other specific studies. Further work along these lines should be conducted, since the present case study yielded results applicable only to the climate of Madrid and similar locations. The research should be extended to address other locations to determine whether the conclusions are climate-dependent. A.R.-P.: methodology, software, investigation, data curation, formal analysis, writing--original draft. E.A.R.J. : methodology, software and validation, investigation, data curation, formal analysis, writing--review and editing. M.C.G. : investigation, validation, writing--review and editing. J.A.T.R. : conceptualization, methodology, validation, formal analysis, supervision, writing--review and editing. All authors have read and agreed to the published version of the manuscript. This research was funded by the European Agricultural Fund for Rural Development (EAFRD) and Spain's Ministry of Agriculture, Fishing and Food under the project 'Grupo Operativo Madera Construccion Sostenible', ref.