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Heat Loss in Humans Warmed with Various Full-body Forced-air Heating Systems. BACKGROUND: Perioperative hypothermia remains a common and preventable complication. Forced-air warming systems are widely used, but comparative data on their effectiveness are limited. This study aimed to evaluate heat flux, mean skin temperature, and thermal comfort across five full-body forced-air warming blower and cover combinations. METHODS: In a randomized crossover trial conducted in a controlled clinical setting, 20 healthy volunteers were each warmed for 30 min using five different forced-air warming systems in randomized order. A 45-min washout period separated each warming session. Cutaneous heat flux and area-weighted mean skin temperature were recorded every 5 min, and thermal comfort was assessed every 10 min. Data were analyzed using repeated-measures ANOVA and linear mixed-effects modeling, with significance defined as P < 0.05. RESULTS: All 20 volunteers completed the trial. Mean age was 29 yr, 40% were women, and mean body mass index was 24 kg/m 2 . Ambient temperature averaged 20.3° ± 2.4°C. Across all warming systems, average heat flux improved from a loss of 101 ± 53 W to a gain of 20 ± 48 W after just 5 min of heating. Skin temperature increased to 35.5° ± 0.8°C within 15 min of warming, remaining stable thereafter. CONCLUSIONS: All five forced-air warming systems transferred substantial amounts of heat. There were no statistically significant or clinically meaningful differences in cutaneous heat transfer, mean skin temperature, or thermal comfort across the systems. Any of the tested systems will therefore prevent hypothermia in most surgical patients.