The lumber industry producing hem-fir, a mixture of western hemlock and amabilis fir, is interested in marketing a termite-resistant wood product in regions where subterranean termites adversely affect consumer confidence in wood-frame construction. The use of borate treatment appears to be a promising approach to overcoming the difficulty of pressure treating unincised hem-fir. This experiment was designed to scientifically confirm whether increasing solution temperatures could increase the penetration of borates into western hemlock, which is the less treatable species of the hem-fir mix. This study was designed to quantify the effect of increasing borate solution temperatures from ambient (approx. 20°C), currently used in commercial treating plants, to 35°C and 50°C on kiln-dried and green western hemlock. Increasing the solution temperature increased the initial uptake in kiln-dried lumber, but the difference was minimal with green lumber. Conversely, the effect of increasing the solution temperature on continued penetration during storage was greater for the green material than the kiln-dried. The kiln-dried samples did not show much movement after two weeks storage, whereas the green material had good diffusion over two weeks, meeting the AWPA standard at 50°C, and would likely continue beyond the two weeks. These results suggest a commercial treating plant will gain optimum penetration of borates using higher solution temperatures on green lumber with a one to two-week diffusion period. Penetration of borate into kiln-dried lumber was also shown to improve greatly using heated solutions, although only the 50°C/4-hour treatment/2-week storage met the AWPA standard in this study.