Abstract Objectives Adherence to continuous positive airway pressure (CPAP) remains an issue, as adverse effects (AE) such as rhinitis, dry/congested nose, dry mouth or throat are commonly experienced. The aim of the study was to compare CPAP efficacy and tolerance in severe obstructive sleep apnea (OSA) patients with or without (w/o) heated humidification using the ThermoSmart system. Methods Multicenter RCT study in which CPAP‐naive patients with severe OSA and meeting one or more of the following criteria: >65 years, using >1 drying medication, previous nasal symptoms or nasal surgery, were included. Patients were randomized to CPAP w/o heated humidification for 1 month and then crossed‐over to the other treatment arm for another month. Naso‐pharyngeal symptoms, Quality of life (FOSQ‐10), sleepiness (ESS) and CPAP compliance and efficacy data were collected. Results Forty patients were enrolled: age 62 ± 9 years, diagnostic AHI 46.7 ± 15.3/hour. About 70% were using >1 drying medication, mainly antihypertensives. Both treatment modalities were found to normalize AHI and decrease sleepiness with no differences between 2 modes, compliance (4.63 ± 0.39 vs 4.70 ± 0.36 h/night) or leaks (32.4 ± 2.0 versus 31.1 ± 1.7l/min). With heated humidification, there was a significant decrease in nasal symptoms such as dry/congested nose. At the study end, 26 patients preferred ThermoSmart ON, 3 did not have preference and 11 preferred ThermoSmart OFF. Conclusion ThermoSmart helps to decrease nose and throat discomfort because of CPAP therapy, these effects did not translate to better compliance but patients had a preference for ThermoSmart.