## 5 Conclusions  
The experiment showed that the thermal modification of wood reduced the intensity of the heat transfer. In comparison with the control sample (natural untreated wood), the thermally modified samples achieved lower final values of heat transfer coefficients in the whole range of measurements. Samples modified at 200 \({}^{\circ}\)C and 220 \({}^{\circ}\)C showed significant differences compared with both the control samples and the samples modified at 160 \({}^{\circ}\)C and 180 \({}^{\circ}\)C. The heat transfer coefficient \(\alpha\) decreased with an increase in the degree of thermal modification. The experiment showed that thermal modification has a positive effect on wood when used as a barrier to heat loss. According to the mean values in Table 2, the heat transfer coefficient was on average reduced by 3% for the 160 \({}^{\circ}\)C sample, at 180 \({}^{\circ}\)C by 9%, at 200 \({}^{\circ}\)C by 28% and at 220 \({}^{\circ}\)C by 44% when compared with the untreated control sample. According to Equation (2), when used in outdoor conditions, the heat transfer will be additionally affected by atmospheric conditions such as humidity, air pressure and the presence and intensity of air flow. The heat transfer coefficient depends on the temperature differences at the interface so the change of the seasons and the alternation between days and nights will also influence its value. The heat transfer coefficient \(\alpha\) also decreased with the gradual heating of the samples. A decrease of the heat transfer coefficient during sample heating followed a model of linear regression. At the beginning of the measurement, the control unmodified sample had a heat transfer coefficient \(\alpha\) = 22.66 Wm-2K-1, which, by the end of the experiment, decreased to \(\alpha\) = 8.6 Wm-2K-1. The decrease was from \(\alpha\) = 21.26 to 8.15 Wm-2K-1 for the 160 \({}^{\circ}\)C sample, 20.09 to 7.36 for the 180 \({}^{\circ}\)C sample, 14.84 to 6.87 for the 200 \({}^{\circ}\)C sample and 11.14 to 5.5 for the 220 \({}^{\circ}\)C sample. When compared with the untreated sample, the heat transfer coefficients of the modified samples at 160, 180, 200 and 220 \({}^{\circ}\)C respectively, decreased to 99%, 93%, 68% and 51% of the maximal control value \(\alpha\) = 22.66 Wm-2K-1 at the beginning of the experiment and to 95%, 86%, 80% and 64% of the minimal value of the control sample \(\alpha\) = 8.6 Wm-2K-1 by the end of the experiment. This decrease could be due to the higher air temperature in the boundary layer. In the presence of heated air, the temperature difference in the proximity above the sample surface was lower than the temperature difference between the sample surface and the ambient air. When compared with studies on the thermal conductivity of thermally modified natural fir and beech wood [12] and spruce and poplar wood [15], similar results were obtained. This study, focusing on the heat transfer coefficient, led to the results being dispersed in a larger range than the results of studies on the thermal conductivity of thermally modified wood [12; 15]. The differences could occur due to multiple factors such as the type of wood, moisture content or variations in the time intervals of the heat treatment. In further experimentation, more samples should be used for testing. An experiment could also be done where holographic interferometry and the hot and cold plate method would be used for the examination of samples of same origin and treatment. The holographic interferometry method shows a potential to be an effective tool in the study of heat transfer by the visualization of temperature fields. It could be applied to a variety of materials such as aerated concrete [28] or to test the functionality of heat exchange surfaces [33]. Holographic interferograms with the use of the Fourier-Mellin transformation could find applications in automation processes by enabling the calculations of shift and the rotation of images [34; 35].