In this article, we present a comprehensive investigation of the photothermal properties of plasmonic nanowire networks. We measure the local steady state temperature increase, heat source density and absorption in Ag, Au and Ni metallic nanowire networks under optical illumination. This allows direct experimental confirmation of increased heat generation at the junction between two metallic nanowires, and stacking dependent absorption of polarized light. Due to co-operative thermal effects, the local temperature distribution in a network is shown to be completely delocalized on a micrometer scale, despite the nanoscale features in the heat source density. The steady state temperature rise is shown to scale linearly with the illumination diameter, allowing calibration of the local temperature field. The total illumination area is thus identified as an important parameter controlling local temperature rise, often not considered in thermoplasmonic experiments. Comparison of the experimental temperature profile with numerical simulation allows an upper limit for the effective thermal conductivity of an Ag nanowire network to be established at 43 Wm-1K-1 (0.1 bulk).