Hello, I have looked through various websites, which show single glazing heat losses (U-factor) to be 5.7 W/m^2.K. But when I use thermal conductivity basic formulas, the yielded results are quite different: k of glass is 1.05 W/m.K; L -> glass thickness is 4 mm = 0.004 m; so: U = k/L = 1.05 / 0.004 = 262.5 W/m^2.K I tried transparent vynil sheets 800 microns thick (vynil-crystal, used as wind shields) and it yields better results, at k = 0.19 for PVC, U factor is about 190 W/m^2.K. This is for an outside "winter garden", which I "single glazed" with vinyl crystal. Currently I am not able to heat it up above 10 degrees celsius, the roof is polycarbonate multi-wall sheet, supposed U factor given from manufacturers 3.4 W/m^2.K. 50 m^2 of room area. So, my main question is, what is the CORRECT heat loss from single glazing? The one from the internet or the one that I have calculated?